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CAMBRIDGE
UNIVERSITY PRESS
Cambridge Lower Secondary
Science
Mary Jones, Diane Fellowes-Freeman & Michael Smyth
CAMBRIDGE
UNIVERSITY PRESS
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Second edition 2021
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Introduction
>Introduction
Welcome to Stage 8 of Cambridge International Lower Secondary Science.
We hope this book will show you how interesting and exciting science can be.
Science is everywhere. Everyone uses science every day. Can you think of
examples of science that you have seen or used today?
Have you ever wondered about any of these questions?
•
What am I made of?
•
Where do all the dead plants, animals and their waste disappear to?
•
Why does frozen water behave differently to liquid water?
•
What happens in a chemical reaction?
•
What is electricity?
•
How did the planets form around the Sun?
You will work like a scientist to find answers to these questions and more. It
is good to talk about science as you investigate and learn. You will share your
ideas with classmates to help them understand, and listen to them when you
need reassurance. You will reflect on what you did and how you did it, and
ask yourself: 'would I do things differently next time?'
You wiJI practise new skills and techniques, check your
progress, and challenge yourself to find out more.
You will make connections between the different
sciences, and how they link to maths, English and
other subjects.
We hope you enjoy thinking and working like
a scientist.
Mary Jones, Diane Fellowes-Freeman, Michael Smyth
iii
>
_______
c_o_n_t_e_n_t_s________________)
>Contents
Page Unit
1 Respiration
1. 1 The human respiratory
system
1.2 Gas exchange
1.3 Breathing
1.4 Respiration
2 Properties of materials
2. 1 Dissolving
2.2 Solutions and solubility
2.3 Planning a solubility
investigation
2.4 Paper chromatography
3 Forces and energy
3. 1 Forces and motion
3.2 Speed
3.3 Describing movement
3.4 Turning forces
3.5 Pressure between solids
3.6 Pressure in liquids and
Science
strand
Thinking and Working
Scientifically strand
Science in Context
Biology:
Structure and
Function
Biology: Life
processes
Models and representations
Carrying out scientific
enquiry
Scientific enquiry: purpose
and plann ing
Scientific enquiry: analysis,
eva luation and conclusions
Discuss how scientific
knowledge is developed
through collective
understanding and scrutiny
over t ime
Describe how science is
applied across industries,
and in research
Evaluate issues which
involve and/ or require
scientific understanding
Chemistry:
Materials and
their Structure
Chemistry:
Properties of
materials
Scientific enquiry: purpose
and planning
Carrying out scientific
enquiry
Scientific enquiry: analysis,
eva luation and conclusions
Describe how science is
applied across industries,
and in research
Physics:
Forces and
Energy
Models and representations
Carrying out scient ific
enquiry
Scientific enquiry: analysis,
eva luation and conclusions
Scientific enquiry: purpose
and planning
Evaluate issues which
involve and / or require
scientific understanding
Carrying out scientific
enquiry
Discuss how scientific
knowledge is developed
through collective
understanding and
scrutiny over t ime
Evaluate issues which
involve and/or require
scientific understanding
D iscuss how the uses of
science can have a global
environmenta l impact
gases
C
0)
3.7 Particles on the move
4 Ecosystems
4. 1 The Sonoran desert
4.2 Different ecosystems
4.3 Intruders in an
ecosystem
4.4 Bioaccumulation
iv
)
Biology:
Ecosystems
Contents
Page Unit
5 Materials and their
structure
5. 1 The structure of the atom
5.2 Purity
5.3 Weather and Climate
5.4 Climate and Ice ages
5.5 Atmosphere and climate
6 Light
6. 1 Reflection
6.2 Refraction
6.3 Making rainbows
6.4 Galaxies
6.5 Rocks in Space
7 Diet and growth
7. 1 Nutrients
7.2 A balanced diet
7.3 Growth, development
and health
7.4 Moving the body
8 Chemical reactions
8. 1 Exothermic reactions
8.2 Endothermic reactions
8.3 Metals and their
reactions with oxygen
8.4 Reactions of metals with
water
8.5 Reactions of metals with
dilute acids
9 Magnetism
9. 1 Magnetic fields
9.2 The Earth as giant
magnet
9.3 Electromagnets
9.4 Investigating
electromagnets
Science
strand
Thinking and Working
Scientifically strand
Science in Context
Chemistry:
Materials and
their structure
Chemistry:
Changes to
materials
Earth and
Space: Planet
Earth
Earth and
Space: Cycles
on Earth
Carrying out scientific
enquiry
Scientific enquiry: purpose
and planning
Models and representations
Scientific enquiry: analysis,
eva luation and conclusions
Describe how people
develop and use scientific
understanding as
individuals and through
collaboration, e.g.
through peer-review.
Discuss how the uses of
science can have a global
environmental impact
Physics: Light
and Sound
Earth and
Space: Earth
in Space
Scientific enquiry: purpose
and p lanning
Carrying out scientific
enquiry
Scient ific enquiry: analysis,
eva luation and conclusions
Models and representations
Evaluate issues which
involve and / or require
scientific understanding
Biology:
Structure and
Function
Biology: Life
processes
Scientific enquiry: purpose
and p lanning
Carrying out scientific
enquiry
Evaluate issues which
involve and/or require
scientific understanding
Chemistry:
Changes to
materials
Scientific enquiry: purpose
and p lanning
Carrying out scientific
enquiry
Scientific enquiry: analysis,
eva luation and conclusions
Describe how science is
applied across societies
and industries, and in
research.
Evaluate issues which
involve and/or require
scientific understanding.
Physics:
Electricity and
magnetism
Earth and
Space: Planet
Earth
Scientific enquiry: purpose
and p lanning
Scientific enquiry: analysis,
eva luation and conclusions
Models and representations
Carrying out scientific
enquiry
Discuss how scientific
knowledge is developed
through collective
understanding and
scrutiny over time.
Evaluate issues which
involve and/or require
scientific understanding.
V
>
_ _ _ _ _ _H_o_w_t_o_u_se_t_h_is_b_o_o_k_ _ _ _ _ _ _ ____,)
>How to use this book
Thjs book contains lots of different features that will help your learning. These are explained below.
This list sets out what you will learn in each
topic. You can use these points to identify the
important topics for the lesson. - - - - - - - - - -
In this topic you wrll:
think about what makes living things different from
non-living objects
learn about t he seven characteristics of living t hings
Getting started
This contains questions or activities to help find
out what you know already about this topic.
In your classroom, find one living thing and one thing which has
never been al ive.
W ith your partner, make a list of things that the living thing can
do, but the non-living thing cannot do.
Be ready to share your ideas with the rest of the class.
Important words are highlighted in the text
when they first appear in the book. You will
find an explanation of the meaning of these
words in the margin. You will also find
definitions of all these words in the
Glossary and Index at the back of
this book.
Jiving
organi!rns
nutrition
growth
movement
non-living
sen1"tivity
resplrEl
exc:r&lton
reproduction
The pie .ure -sho·•A":. a c.ar.
Here :are s,..m,e fa...ts. ~ ::,uu1 ;_:at"..,_
C.:at-: J-;;e il el .at.J ury'!-lctl
ti--.i;~,r. th~ ~t,-qin~ ;)...: th~ ...11r, t·,-r. fud
anJ ory~en oroviJe ertergy Lo "flake
You will have the opportunity to practise and
develop the new skills and knowledge that
you learn in each topic. Activities will involve
answering questions or completing tasks.
the cc'3r trove.
The e-t~gire produces wast-!.'! gases!
1t,.;; ut -,g \.',~•bo" d1v'X de T·,csc t."<"
;.: iven __,ff ·•1 th~ e:t!1.au:,t uf d ~ c~r.
S-01n~ ;· ~h h<'lv~ =--~t,~;)":'> Fm ~x<'!rr'lpl~, th~y •· 'rn .;,~1,~<".' wh~r,
il i, da,k anJ Lurn Lre ligh. on auloMalically.
Questiotis
►
M•ki119 • model of• p l•11t cell
lt1 t·,1s act1v1ty, you ·,t,• II mtikE" a mocel to represet1t ~ ce- I. ' (ou will t·,e·, th1rk about tf·e
•~-:•("'i,gth~ M,d l1t""lr:,~t1;-:,i,~ ,~f yrnn rrnd<""I
He(<" 1:3. GI 11st ::Jf '"r'lir:cr1dls <'It'd ::JbJects you ;:ouk~ l.sc tv ttiilk<" your rr"odd
• trimsp2Jrerit boxes
This provides an opportunity
for you to practice and develop
scientific enquiry skills with a
partner or in groups.
)
• St"nJJII ~md lvtge pl2Jst1G O-:>JS filled with 'NlJ-:er
• ;,::l1t,,g f1lrr" {tn:rnsptirerit food ·•Nr.vp)
• .:zirdbvard bo}:.es of v:?Jnous sizes
• so·l'Je g"f:"etl grt!pes
• etr O~' plast1-c- a:l,::JS
• pu..,ple grzipes
• Plastkit~t•$
lr1 yOJr g-oup, <.lecide ~ow you car1 use -soMe o' Lhe~e rr"'lalerials ar-d obj eel~ Lo rr"ake a
,-,od,I of a plant c,11. Th,n rn•k• yoJr ,-,od,I.
ee ready to exp lair your tnod el to others.
Questions
vi
• cJrdbovtd boxes
• iJref:"r, oe,:;;is or qre~r, oE-:iids
How to use this book
►
Tl-ink aboul how y·ou did Lhis task.
Fut ead1 uf thc-<.,e ":.>fatement':.>, rate yuut!.elf:
After completing an activity, this provides you
with the opportunity to either assess your own
work or another student's work. - - - - - - - - --
T his contains questions that ask you to look
back at what you have covered and encourages
you to think about your learning.
►
T his list summarises t he important topics that
you have learned in the topic. - - - - - - - - - --
if yuu JiJ ·L quile
well, or tleedeC
some hep
i( yul l~1ink y0u
did ·1 verv well,
with no.help
1
if yul Jidt1 l .;.;u
i1 :a l, or ,,eeded
" lot of h<'lp
I .;_ut 3 r·~;,_,t: Jf tf e it1siJe layt:=r uf ut i-ut1 :hat \'-/~S abus:
1 ,...h1 <:~Jt.:
,r~
How have your tned to remember the d ifference between a cell wall
and a cell membrane1 How successful do you think you have been?
Summary checklist
"\
I can list the seven characteristics of living things
I can describe the meaning of each of these characteristic,
At the end of each unit, there
is a group project that you can
carry out with other students.
This will involve using some of
the knowledge that you
developed during the unit.
Your project might involve
creating or producing something,
or you might all solve a problem
together.
I hi:, prujed i-.; al.,uut !i;,.f,J>J s~ie,1ti.!i~ ktH,_.f,,.JieJ'i-le qroJu.ally Jeve u:.:.,,s uver titni:;:. Yul a r-:-
goir1g to ·•,\•ork in a ~.,,oup lo de research, and Lher1 L -se you.,, rir1dir1gs .o rtelp Lo '1'1ake a
tirne- l1tH"
Sti-e-tK:e tH'!\-'er 'St:Jys -stil . v~1her1 ore -sdentist rn;;ike-s .:l tH'!"i/>.' di-stover;, this suggests ,,e-w
q11 .....~tl;)m: t-,~- ;)th.....r ~<".l<'"tlh ..t~ <".?m IIW('-~t u~t<"
Yol1 qrc 901r9 to help to prodUi.':C- Q twnc me T~•c tlt'ndmc -.,..11 s·,vw hvw :s:t1:::,,t sts
~r,H.:uallyJi~~-:.JvereJ d1at .al li'1inH thinq:, are maJe uf-:...e I::..
HN~ <"Jr~ ~,..,r1~ ;)-= th~ itnp;)tt<'lnt -;1~p-·, th_.,,t ;);-n ~r~.J Y,)1Jr t~.f'd•~r wil 11 l:K.-c'Jt~ m1~ ()t h •J;)
of these SL,eps .o your group. YoJ will Lhen ,,elp Lo 'incl oul More abou. these ,Leps, anc
ptv Juce :ar, illustuited :ac..:ourit of wh:at h<lppereJ. Tr/ -:o ir,..: JC-et.'' -E-xpl,m.:ltiot, of hmN
th<" '•h'i':irk >)f <";,rl1N ~<".l<"tltl-:.t-:. h<"'lp. . .d th1~ ,:_-,...p -;) t.r'lk<"' rl,K<"'
1625 Galileo Gali "i builds the iirst microscope.
1665 Rober! Hecke looks a cork 1/rorr tree bark) 1,,rougl- a roicrosco,,e. and describes
t1..,
These questions look back
at some of the content you
learned in each session in this _____...
unit. If you can answer these,
you are ready to move on to
the next unjt
,
CfJ
Check your Progress
Difft=ct:ntcelh hrt.Vt dift r,e-nt funct itrn.:i.
Cho n.;in~ (,nm U,i.; li:-1, ti~ rr'l i.'" 1l,;.• -:.:;...-11 1.hal ;.•;.,ich fnn-.·linn tk.:.c:1 ih..::s
red blood cell
c
root hair cell
palinde cell
t1erve cell
ciliated cell
Mak.es food by photo,ynti1t>1~
(3]
►
vii
)
>Science Skills
Laboratory apparatus
beaker
test
tube
boiling
tube
-
200
-
ISO
-
100
-
CSO
graduated
beaker
conical flask
funnel
100
7V
80
70
60
40
syringe
30
spatula
forceps
glass rod
20
measuring
cylinder
dropper
pipette
thermometer
metre
rule
burette
timer
lamp
force meter
mortar
0
candle
boss
clamp
Petri dish
mounted
needle
tripod and gauze
Bunsen burner
/» 1,•.•••
top pan balance
viii
)
microscope slide
microscope
retort stand
Science Skills
Making better measurements
In Science, we often take measurements. We do this to find out more about
something that we are interested in.
Measurements are taken using measuring instruments. These include rulers,
balances, timers and so on.
We want our measurements to be as accurate as possible. In other words, we
want them to be as close as possible to the true answer. Then we can be more
confident that our conclusions are correct.
Measuring instruments
How can we be sure that our measurements are as accurate as possible?
We need to think about the instruments we use. Here are two examples:
•
You want to measure a 50cm3 volume of water. It is better to use a 100 cm3
measuring cylinder than a 50 cm3 beaker, even though the beaker may have
a line indicating the level which corresponds to 50cm3• A 100cm3 measuring
cylinder is better than one which measures l 000 cm3 because 50 cm3 is only
a small fraction of 1000cm3 •
•
You want to time a toy car moving a distance of I .Om. You could use the clock
on the wall, but th is is not a good choice as it is not accurate. You could use a
stopwatch, but it is tricky to start and stop the watch at the exact moments when
the car crosses the starting and finishing lines. You would have to take account of
your reaction time. It is best to use light gates since these automatically start and
stop as the car passes through. The gates are connected to a timer which will show
you the time taken to within a fraction of a second.
light gate
~
timer
Choose an accurate method of measurement.
ix
)
______
sc_i_e_n_c_e_S_k_il_ls_ _ _ _ _ _ _ _ _ _ ____,)
We also need to think about how we use measuring instruments.
For example:
•
When using a ruler to measure the length of an object, the ruler
needs to be placed directly alongside the object. Make sure that
one end of the object is exactly next to the zero of the ruler's scale.
Don't do it like this. You might think the end of the leaf stalk is at
0 cm but it is actually at 0.2 cm.
•
When using a measuring cylinder, look horizontally at the surface
of the liquid and read the scale level with the bottom of the meniscus.
60
meniscus
50
40
Don't do it like this. You might read this as 48, when it should be
read as 45.
•
When using a balance to weigh an object, check that it reads zero
when there is nothing on it. Similarly, a forcemeter should read zero
when no force is pulling on it. It may be possible to reset these
instruments if they are not correctly set to zero.
Don't use it like this.
X
>
Science Skills
Improving accuracy
You can see that to make your measurements as accurate as possible, you need to think
carefully about the measuring instruments you use and how you use them.
It can help to make repeat measurements; measure the same quantity several times and
then to calculate the average.
With practice, you will find that your measurements become more accurate and so you
will be able to trust your findings more.
Anomalous results
Sofia did an experiment to find out how light intensity affects the rate of photosynthesis
of a water plant. She placed a lamp at different distances from the p lant, and counted the
number of bubbles it gave off in one minute.
Paula made three counts for each distance of the lamp from the plant. This table shows
her results.
Distance of lamp
from plant / cm
20
40
60
80
Number of bubbles per minute
1st try
2nd try
28
19
12
8
29
33
14
10
3rd try
27
18
13
10
Paula thought that one of her results didn't look right. Can you spot which one it is?
A result like this, that does not fit the pattern of all the other results, is called
an anomalous result.
If you get something that looks like an anomalous result, there are two things that you
can do.
1
The best thing to do is to try to measure it again.
2
If you can't do that, then you should ignore the result. So Paula should not use this
result when she is calculating the mean. She should use only the other two results for
that distance from the lamp, add them up and divide them by two.
Spotting an anomalous result in a results table can be quite difficult. It is often much easier
if you have drawn a graph.
Arun did an experiment to investigate how adding ice to water changed its temperature.
He added a cube of ice to 500cm3 of water and stirred the water until the ice had completely
melted. Then he measured the temperature of the water before adding another ice cube.
The graph on the next page shows his results.
xi
)
>
Science Skills
15 ...:
ii-
X
I=I --1-I
t
i-
r
t
10 -
rt
I
I
I
X
1- i- 1i-
- t--
t
i-
i
ii-
r
X
i-
t
t
i-
ii-
I
0
--~'-_,
__
ii-
r
0
~,--
I
i-
5 -
·-~
=t
i-
temperature in °C
1
I
I
I
I
I
2
3
number of ice cubes
X
I
-- -
X
I
I
4
5
It's easy to see that the point at (3, 3) doesn't fit the pattern of all the other results.
Something must have gone wrong when Arun was making that measurement.
When Arun draws the line on his graph, he should ignore this result. He should also
think about why it might have gone wrong. Perhaps he misread the thermometer was the correct reading 8 °C? Or perhaps he forgot to stir the water and measured the
temperature where the cold ice had just melted. If you think about why an anomalous
result has occurred, it can help you to improve your technique and avoid such problems
in the future.
temperature in °C
0
1
2
3
4
Ignore the anomalous result
when you draw the line.
xii
)
5
Science Skills
Understanding equations
In Topic 3.2 Speed, you studied three equations which relate speed, distance
and time. Here are the three equations:
speed
_ distance
time
distance
= speed x time
time
_ distance
time
How can you remember these three equations? It will help if you think about
the meaning of each quantity involved. It can also help to think about the units
of each quantity.
Speed is the distance travelled per second or per hour. The word ' per' means 'in each',
and this should remind you that the distance must be divided by the time.
Another way to think of this is to start with the units. Speed is measured in metres
per second, so you must take the number of metres (the distance) and divide by the
number of seconds (the time).
Distance is how far you travel. The faster you go (the greater your speed), and the
longer you go for (the greater the time), the greater the distance travelled. This tells
us that the two quantities must be multiplied together.
The train is travelling at 75 m/s.
Time to pass observer = 3.6 s.
length of train = speed x time
= 75 X 3.6
= 270m
xiii
)
Respiration
> 1.1 The human respiratory system
In this topic you will:
•
learn the names of the d ifferent parts of the human
respiratory system
•
observe careful ly, and record your observations, as the
structure of lungs is demonstrated
Getting started
words
aerobic respiration
Respiration is one of the characteristics of living things.
air sac
With a partner, decide which statement in each pair is correct.
bronchiole
Be ready to share your ideas.
First pair:
Second pair:
Third pair:
Respiration happens
inside all the cells in
your body.
~
bronchus
or
Respiration releases
energy from food.
or
Respiration happens
in all living things.
or
Respiration only
happens in cel ls
in your lungs.
Respiration uses
up energy.
Respiration
happens in animals
but not plants.
cartilage
larynx
~
respiration
respiratory systen
trachea
vocal cords
1.1 The human respiratory system
Why we need oxygen
You may remember that one of the characteristics shared
by all living things is respiration. Respiration is a series of
chemical reactions that happens inside every living cell.
The kind of respiration that usually happens inside our cells
is called aerobic respiration. Aerobic respiration uses oxygen.
The cells produce carbon dioxide as a waste product.
The air around you contains oxygen. When you breathe,
you take air into your lungs. Some of the oxygen from the
air goes into your blood. The blood delivers the oxygen
to every cell in the body, so that the cells can use it for
respiration. The blood collects the waste carbon dioxide
from the cells, and takes it back to the lungs.
The organs that help you to take oxygen out of the air, and
get rid of carbon dioxide, make up the respiratory system.
Can you name any of the other organs shown in the picture?
In t his model of the human body, t he lungs are
shown in pink
The structure of the human
respiratory system
This is a diagram of the human
respiratory system. The white
spaces in this diagram are the
entrance to mouth ' tubes' that air moves through,
as it goes into and out of
voicebox (larynx)
your lungs.
windpipe (trachea)
rings of cartilage ==~::3;:z:::~===:::::::;;t
lung
bronchiole
air sacs
rib bone
muscles between ribs== '1=-== =P!!
(intercostal muscles)
diaphragm
The human respiratory system.
3
>
______1__
R_e_sp_i_ra_t_io_n_ _ _ _ _ _ _ _ _ _ ___,)
Questions
Put your finger on the entrance to the nose or mouth in the diagram
of the respiratory system. Move your finger along the white space
and down into the lungs.
1
Write down the structures that the air passes through, as it moves
down into your lungs. Write them in the correct order.
Now write the same structures in the order in which air passes through
them as it moves out of your lungs and back into your surroundings.
2
Air gets into your body through your mouth or nose. Your mouth and nose
both connect to your trachea. The trachea is sometimes called the windpipe.
It has strong rings of cartilage around it. These rings of cartilage keep the
trachea open and prevent it collapsing so that air can be kept moving in
and out of your body. If you put your fingers on the front of your neck and
move them downwards, you can feel the rings of cartilage on your trachea.
The trachea branches into two bronchi (singular: bronchus). The bronchi
also have cartilage to support them. One bronchus goes to each lung.
Each bronchus carries air deep into the lungs. Each bronchus divides
into several smaller tubes called bronchioles. These structure of these
branches allow the air to reach deeper into the lungs.
The bronchioles end by branching into many tiny structures called
air sacs. This is where the oxygen goes into the blood, and the carbon
dioxide comes out. You can find out more about this in the next topic.
Think like a scientist
-
C
Looking at lungs
In this activity, you are going to look carefully at some real lungs. You will practise using
your senses of touch and sight, to make observations, and recording your observations.
Before you start this activity look carefully at the questions and make a risk assessment.
Think about how you will reduce or overcome any risks. be prepared to share your ideas.
You will need:
•
a set of lungs from an animal, such as a sheep or goat (from a butcher)
•
a big board to put the lungs onto
•
hot water, soap and towels to wash your hands after handling the lungs
Ouest ions
1
Describe what the lungs look like.
If you prefer, you could make a labelled drawing instead of writing about them.
4
>
1.1 The human respiratory system
Continued
2
Touch the lungs.
What do they feel like when you push them? Can you suggest why they feel like this?
(Look at the diagram of the human respiratory system to help you.)
3
Look at the tube that carries air down into the lungs.
a
What is the name of this tube?
b
Feel the tube. What does it feel like?
c
Follow the tube towards the lungs. Can you find where it divides into two?
What are the names of these two tubes?
d Now look at the top of the big tube, where it is wider.
What is the name of this wide part? What is its function?
The diagram of the respiratory system includes a lot of new words.
How are you going to learn this diagram and all of its labels?
Remember that, in a test, the diagram might not be exactly the
same as this one.
Activity 1 .1 .1
..C
What does the larynx do?
Hold the fingertips of one hand against your larynx (voicebox).
Keep your lips together, and make a loud humming sound.
Can you feel the larynx vibrating?
Your larynx contains your vocal cords. These are bands of muscle that stretch across your
larynx. You can think of them as being rather like guitar strings. When these cords vibrate,
they make a sound.
Now make a higher-pitched humming sound. Then try a really deep pitched one.
Can you feel the larynx changing when you make the different sounds?
~
Summary checklist
I can name the parts of the respiratory system, and identify them on a diagram.
I can list the organs that air passes through, as it moves into and out of the lungs.
5
>
1 Respiration
)
> 1.2 Gas exchange
In this topic you will:
•
find out how oxygen gets into your blood from the air, and
how carbon dioxide goes in the other direction
•
do an experiment to help you to think about why the air sacs
in the lungs need to be very small
•
do an experiment to compare how much carbon dioxide
there is in the air you breathe in and the air you breathe out
Getting started
Key words
This topic is about two gases - oxygen and carbon dioxide.
alveoli
Look at these diagrams.
analogy
.--. ... ..• •
.-.. .. -....
•.. •.. ,,, .. ., ., .."' -
A
~ ~
8
~
:=
...
B
<!!I
.... .. .. .,-.. .. ..----.. -.. ..-.. -
"" "' "'
-
C
e....
t
8 _Q
....Q
Q-
~
't
,
Q ft
Q .,..
capillaries
diffusion
expired air
gas exchange
haemoglobin
inspired air
limewater
With your partner, answer these questions.
1
Which diagram shows the particles in a gas?
2
Choose the correct phrases to complete these sentences:
In a gas, the particles are far apart I touching each other.
In a gas, the particles move freely I vibrate on the spot.
6
>
1.2 Gas exchange
Air sacs
The photograph shows a tiny part of the lungs, seen through a powerful
microscope. You can see the lungs are mostly holes. These holes are
called air sacs. Another name fo r them is alveoli.
There are also lots of very tiny blood vessels in the lungs, wrapped
around the air sacs. You cannot see them in the photograph, but they
are shown in the diagram below. These blood vessels are capillaries.
Part of the lungs, viewed
t hrough a powerful
microscope
The structure of an air sac
This diagram shows one of the air sacs in the lungs. The air sac has
a wall made of one layer of cells. These cells are very thin.
air moving in
air moving out
blood flowing
towards t he
--=~= heart
blood flowing
from the hea~
diffusion
of oxygen
thin wall of
-----+I-~
blood capillary
--'<\\
red blood cell - -~ ._.
blood plasma
An air sac in the lungs
You can see that there is a blood capillary around the outside of the
alveolus. The capillary is pressed tightly against the alveolus. The wall
of the capillary is a lso made of a single layer of very thin cells.
7
>
______1__
R_e_sp_i_ra_t_io_n_ _ _ _ _ _ _ _ _ _ ___,)
Gas exchange in the air sacs
Inside the air sacs, oxygen from the air goes into the blood. Carbon
dioxide from the blood goes into the air. This is called gas exchange.
Think about the blood capillary on the left of the diagram. The blood
inside this capillary comes from the heart. Before reaching the heart,
it came from the organs in the body. These organs contain cells that
respire, using up oxygen and making carbon dioxide. So, the blood in
this capillary contains only a small amount of oxygen, and a lot of
carbon dioxide.
Now think about the air inside the air sac. It came from outside the
body, where the air contains a lot of oxygen and only a small amount of
carbon dioxide.
Inside the alveolus, this air is very close to the blood. There are only two
very thin cells between the air and the blood.
The oxygen particles in the air are a gas, so they are moving freely. They
can easily move from the air, through these thin walled cells and into the
blood. This is called diffusion. You can find out more about diffusion
in Topic 3.7. The oxygen molecules move from where there are a lot of
them (in the air) to where there are fewer of them (in the blood).
When the oxygen gets into the blood, it dissolves. (You can find out
about dissolving in Topic 2.1.) It goes into the red blood cells where it
combines with haemoglobin. You will find out what happens to it after
that in Topic 1.6.
Now think about the carbon dioxide. There is a lot of it in the blood in
the capillary, and only a small quantity in the air inside the air sac. So,
the carbon dioxide diffuses into the air in the air sac.
:....
Activity 1.2.1
Gases in and out
Copy this diagram.
8
1
On your diagram, draw a green arrow to show how
oxygen diffuses from the air into the blood.
2
How many cells does the oxygen move through, as it leaves
the blood and goes into the air?
3
On your diagram, draw a blue arrow to show how carbon
dioxide diffuses from the blood into the air.
>
(1)
1.2 Gas exchange
Think like a scientist
Why are air sacs so small?
In this activity, you will use some agar jelly to represent the lungs, and some coloured
liquid to represent oxygen in the air.
You will need:
• two Petri dishes filled with agar jelly
• two cork-borers, one with a diameter of 10 mm and the other with a diameter of 5 mm
• some coloured dye
• a dropper pipette
Method
1
Use the larger cork-borer to make eight holes in the jelly in
one of the dishes. Space the holes evenly in the dish.
2
Now use the smaller cork-borer to make 32 holes in the jelly
in the other dish. Try to space the holes evenly in the dish.
3
Using the dropper pipette, careful ly fill each hole in both
dishes with the co loured dye. Try to put the same quantity
of dye into each hole. It's rea lly important not to get any
dye on the jelly!
4
Leave both dishes for at least 15 minutes.
5
Predict what you think will happen.
6
After 15 minutes (or a little bit longer if things are happening slowly)
record your observations.
Questions
1
The holes that you made in the jelly represent the air sacs in
the lungs. The coloured dye represents oxygen in the air sacs.
The holes in the jelly are an analogy for the air sacs, and the
dye is an analogy for oxygen.
Explain how your observations help to show what happens to oxygen in the lungs.
2
The tota l volume of the 32 small holes is the same as the total volume of the eight
large holes. Use your observations to suggest why it is better to have a lot of very
small air sacs in the lungs, rather than just a few large ones.
3
Do you think that the agar jelly with holes is a good model for what happens in
the lungs? Explain your answer.
9
>
______
1_R_e_s_p_ir_at_i_o_n_ _ _ _ _ _ _ _ _ _ _ _)
Think like a scientist
Comparing the carbon dioxide content of inspired air and expired air
In this activity, you will use limewater to compare how much carbon dioxide there
is in the air that you breathe in and the air that you breathe out.
Work with a partner to do this activity.
You will need:
• rubber tubing
• glass tubing as shown in the diagram
• two rubber bungs to fit the test tubes
• 2 test tubes
• limewater
Safety
It is very important that the rubber tubing is perfectly
clean before you use it . Do not share the mouthpiece
with anyone else or put it on the work surface when
you have finished.
rubber tubing
glass tubing
rubber bung
Method
1
Read through the method and make an
assessment of all the risks and decide how
you wi ll overcome or reduce these risks.
2
Look carefully at the apparatus.
Starting with the rubber tubing, follow the
glass tube as it branches into the two test tubes.
test tube
-1-------1++---=t=== limewater
A
s
What is different about the glass tubing that goes into test tube A and test tube B?
Now think about what might happen if you gently blow down the rubber tube.
3
Predict the tube in which you think bubbles will appear. Why do you think that?
4
Gently blow into the rubber tubing, until bubbles appear in one of the tubes.
Was your prediction correct?
5
Now think about what might happen if you gently suck the rubber tube. Try it.
Was your prediction correct?
6
Put your mouth over the end of the rubber tubing, and gently breathe in and out.
Bubbles wil l appear in one tube as you breathe out, and in the other tube as you breathe in.
Your partner will check the bubbles and can tel l you if you are doing it correctly.
Be careful - don't suck too hard! Limewater is not poisonous, but it is not a good
idea to get it into your mouth.
7
10
Continue until the limewater in one of the tubes has gone cloudy. Make a note of
which tube it is.
)
1.2 Gas exchange
Continued
Questions
1
The air that you breathe out is called expired air.
In which tube did your expired air bubble through the limewater?
2
The air that you breathe in is called inspired air.
In which tube did your inspired air bubble through the limewater?
3
In which tube did the limewater go cloudy first?
4
Name the gas that makes limewater go cloudy.
5
Copy and complete these sentences. Use some of these words:
A
B
expired
inspired
less
more
The limewater went cloudy first in tube _ _ _ _ __
This is the limewater that _ _ _ _ _ _ air bubbles through.
Our results show that expired air contains _ _ _ _ _ _ carbon dioxide than
inspired air.
Self-assessment
Think about how you did the experiment.
Copy each statement, and then draw a face next to each one according to how well
you think you performed.
@ I think I did this really well.
@ I did OK, but I could probably do better.
@ I didn't do this very well at all.
•
I worked out which tube the air would go into when I breathed in and when I
breathed out.
•
I managed to breathe in and out with just the right force to make the air bubble
through the limewater.
•
I stopped as soon as the limewater in one of the tubes went cloudy.
•
I understand what this experiment shows about how much carbon dioxide there
is in inspired air and expired air.
Is there anything that you would do differently if you did this experiment again?
11
)
_ _ _ _ _ _1__
R_e_s_p_ir_a_ti_o_n_____________,)
Summary checklist
D
I can describe how oxygen gets into my b lood from the air, and carbon dioxide
goes the other way.
D
I can explain why it is better to have lots of very sma ll air sacs in the lungs, rather
than a few b ig ones.
D
I can describe how to do an experiment to compare how much carbon dioxide there
is in inspired air and expired air.
1.3 Breathing
> 1.3 Breathing
•
measure how much air you can push out of your lungs in one
breath
•
learn how the muscles between your ribs and your diaphragm
move air into and out of the lungs
Getting started
Key words
On your own, answer each of these questions.
breathing
contract
•
What is gas exchange?
•
Where does gas exchange happen in your body?
•
Does the air you breathe in contain more or less oxygen than
the air you breathe out?
•
Is there any carbon dioxide in the air you breathe in?
•
Do you think there is any oxygen in the air you breathe out?
relax
0
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C
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E
0
13
)
_ _ _ _ _ _1_R_e_s_p_ir_
at_i_
o _n_ _ _ _ _ _ _ _ _ _ _ _)
How much air do you use?
Think like a scientist
Measuring the volume of air you can push out of your lungs
How much air do you think you can push out of your lungs in one breath?
In this experiment, you will use some very simple apparatus to find out.
You will need:
• a big plastic bottle with a lid
• marker pen
• water
• measuring cylinder
• bendy tubing
• big bowl
Safety
The bottle and bendy tubing must be clean, and the water you use must be safe to d rink.
You may get water on the floor as you do your experiment. Take care not to slip in it .
Method
1
You are going to use the plastic bottle to measure volumes.
In your group of three, discuss how you can use the measuring cylinder to mark
a scale on the plastic bottle.
Then mark the scale on the bottle. The scale should go all the way from the
bottom to the top of the bottle.
2
Fill the bottle right to the top with water. Put the lid on.
3
Pour water into the big bowl until it is about half full.
Turn the bottle upside down, and hold it in the bowl.
Very carefully take the lid off the bottle. You should find
that all the water stays in the bottle.
4
Carefu lly slide the bendy tubing into the top of the
bottle, under water.
5
Take a deep breath in, then put your mouth over the
tubing and breathe out as much air as you can through
the tubing. Your expired air will push out some water
from the bottle.
Use the scale that you drew on the bottle to record the
volume of air you breathed out.
6
14
If you have time, repeat steps 2 to 5 two more times. Use your three results to
calculate a mean value for the volume of air you can breathe out of your lungs.
)
1.3 Breathing
Continued
7
Replace the tubing with another piece of clean tubing. Now another person
in your group can try the experiment.
8
Record all of your results in a table.
Questions
1
2
Share your results with the rest of the class. Can you see any patterns in the resu lts?
For example:
•
Do you think that the volume of air a person can breathe out is related to their size?
•
If there is anyone in your class who plays a wind instrument, does this seem to
have an effect on how much air they can breathe out?
Plan an experiment to investigate this hypothesis:
People who play the trombone can breathe out more air in one breath than people
who play the violin .
Cl
(.)
--
Activity 1.3.1
~
What happens when you breathe in?
Sit quietly for a moment. Shut your eyes and think about your breathing.
Put a hand just underneath your ribs. Take a deep breath in. You may be able to
feel your ribs moving upwards. You might also be able to fee l something moving
inwards as you breathe.
15
)
______1__
R_e_sp_i_ra_t_io_n_ _ _ _ _ _ _ _ _ _ ___,)
Breathing
Look at the diagrams of the human respiratory system, in Topic 11.1. Find
the ribs, and the intercostal muscles between them. Find the diaphragm.
Remember that air is a gas. The pressure of a gas increases when the
volume of its container is decreased. You can find more about pressure
in Topic 3.6 Pressure in liquids and gases.
When you breathe in, these things happen:
•
The intercostal muscles between the ribs
contract (get shorter). This pulls the ribs
upwards and outwards.
•
The muscles in the diaphragm contract. This
pulls the diaphragm downwards.
•
These two movements make more space
inside the chest cavity. They increase the
volume inside it.
•
When the volume increases, the pressure
inside the chest cavity and lungs decreases.
•
Air moves down through the trachea into the
lungs, to fill the extra space.
When you breathe out, these things happen:
•
The intercostal muscles between the ribs relax
(return to normal size). This allow the ribs to
d rop down into their natural position.
•
The muscles in the diaphragm relax. This
allows the diaphragm to become its normal,
domed shape.
•
These two movements make less space inside
the chest cavity. They decrease the volume
inside it.
•
When the volume decreases, the pressure
increases. So air is squeezed out of the lungs.
16
)
air moves into lungs
air moves out of lungs
1.3 Breathing
Think like a scientist
Using a model to represent breathing movements
You will need:
• rubber bung with a hole in it
• syringe with end cut off
1
Carefully and steadily, pull the plunger of the
syringe out. Note what happens.
2
Now push the plunger back in again.
Note what happens.
3
• balloon
small hole
rubber bung
syringe with end cut off
Which parts of the model represent these
structures in the body?
balloon
•
the lungs
plunger
•
the trachea
•
the diaphragm
•
the rib cage
4
Explain why the balloon inflates when you pu ll the
plunger out.
5
Explain how pulling the plunger out represents what
happens in your body when you breathe in .
6
Describe one way in which this model does not completely
represent what happens when you breathe in.
Questions
1
Copy and complete this table.
Use these words:
contract
relax
Action
Breathing in
Breathing out
What do the diaphragm
muscles do?
What do the intercostal
muscles do?
\
-z
'"T
17
)
______
1_R_e_s_p_ir_a_t_io_n_____________)
Copy and complete these sentences.
2
Use these words:
decrease
increase
into
out of
When we breathe in, the muscles in the diaphragm and between the
ribs _______ the volume of the chest. This makes air move
_ _ _ _ _ _ the lungs.
When we breathe out, the muscles in the diaphragm and between the
ribs _ _ _ _ _ _ the volume of the chest. This makes air move
_______ the lungs.
Summary checklist
D
D
D
D
18
I can use a measuring cylinder to make a volume scale on a bottle.
I can do an experiment to measure the volume of air I can breathe out in one breath.
I can describe how the diaphragm and intercostal muscles cause b reathing movements.
I can explain how these breathing movements make air move into and out of the lungs.
)
1.4 Respiration
> 1.4 Respiration
In this t opic you wil l:
•
find out how every living cell gets the energy it needs to stay
alive
•
do an experiment to investigate how, in respiration, some
energy is released as heat
•
think about the difference between breathing and respiration
Getting started
Key words
Think back to Stage 7, where you learned about energy.
g lucose
mitochondria
With a partner, think about this question:
What has to happen to energy, in order to make something
happen?
Can you give some examples?
Be ready to share your ideas.
19
)
______1__
R_
e_
sp_i_ra_t_io_n_ _ _ _ _ _ _ _ _ _ ___,)
Using energy to stay alive
Our bodies need energy for many different reasons. For example:
We use energy when we
move around.
We use energy to send
electrical impulses along
neurones.
We use energy to keep ou r
bodies warm when it is cold.
All of our energy comes from the food that we eat. Carbohydrates are
especially good for giving us energy.
When we eat food containing carbohydrates, our digestive system breaks
the carbohydrates down to a kind of sugar called glucose. The glucose
goes into our blood. The blood delivers glucose to every cell in the body.
The cells use the gl ucose to get the energy that they need.
Releasing energy from glucose
Energy must be changed from one type to another, or be transferred,
in order to do something.
The energy in glucose is locked up inside it. Glucose is an energy
store. Before your cells can use the energy, it has to be released from
the glucose.
This is done by tiny structures called mitochondria that are found
inside cells. Most cells have many mitochondria inside them.
Mitochondria release energy from glucose, so that the cells can
use the energy.
The mitochondria carry out a chemical reaction called aerobic
respiration. Aerobic means that is uses oxygen, from the air.
H ere is the word equation for aerobic respiration:
glucose + oxygen ~ carbon dioxide + water
In this reaction, some of the energy inside the glucose is released.
This is done in a very controlled way. Just a li ttle bit of energy is
released at a time - just enough for the cell's needs.
20 )
-
glucose
oxygen
water
carbon dioxide
A cell with a mitochondrion inside
1.4 Respiration
Questions
1
Neurones contain more mitochondria than cheek cells. Suggest why.
2
Look at the word equation for aerobic respiration.
3
a
What are the reactants in this reaction?
b
What are the products of this reaction?
Use the equation for aerobic respiration to explain why the air that
you breathe out contains more carbon dioxide than the air that you
breathe in.
Respiration and heat production
In Stage 7, you learned that every time energy is transferred, or
transformed, some of it is changed to heat energy.
In respiration, chemical energy stored in glucose is transferred to other
substances, so that cells can use it. In this process, some of the energy
is changed to heat energy. So respiring cells get a little bit warmer than
their surroundings.
Think like a scientist
Investigating respiration in peas
All living things need energy. So all living things respire. Even seeds respire .
Seeds respire especially quickly when they are germinating, because they need a lot of
energy to do this. You can make pea seeds start to germinate by soaking them in water
for about an hour.
You will need:
• 2 thermometers
• cotton wool
• 2 flasks
• insulating material to wrap round the outside of the flasks
• some dead peas
• the same number of live, germinating peas
21
)
______1__
R_e_sp_i_ra_t_io_n_ _ _ _ _ _ _ _ _ _ ___,)
Continued
Method
Set up your apparatus
as shown in the diagram.
Take care to make
everything exactly the
same in each piece of
apparatus. The only
difference is that one
flask contains dead peas,
and the other flask
contains live,
germinating peas.
1
2
Measure the temperature
inside each flask.
Record it in a results chart.
3
Continue to measure and
record the temperature at
regular intervals. For example,
you could do this every hour
during the school day.
4
thermometer
- --ill
cotton wool
l:iilask
insulating -------tsa11
material
wrapped
round the
outside
dead peas
live, germinating peas
Display your resu lts as a line graph.
•
Put time in hours on t he horizontal axis.
•
Put temperature in °C on the vertical axis.
•
Plot the points for the live peas as neat crosses.
•
Plot the points for the dead peas as dots with a circle around them .
•
Join the points for each set of peas with ruled, straight lines between the points.
Questions
1
What was the variable that you changed in this experiment?
2
Which variables d id you keep the same?
3
Which variable did you measure?
4
Suggest an explanation for your results.
5
If you did the experiment again, would you expect your results to be exactly the
same? Explain your answer.
6
Suggest any improvements you wou ld make to your experiment, if you were able t o
do it again. Explain why each of your suggestions would improve your experiment.
22
)
1.4 Respiration
Activity 1.4.1
Thinking about a thermogram
The photograph is a thermogram of a woman working at
her computer.
The colours on the photograph show the temperatures
of the different objects.
In a group of three, think about the photograph, and
discuss these questions. Be ready to share your ideas.
1
Which object in the photograph has the highest
temperature? Can you suggest why?
2
What is the approximate temperature of most of the woman 's body?
3
Explain why the woman 's body has a higher temperature than the chair she is sitting on.
-
C)
Activity 1.4.2
Explaining the difference between breathing and respiration
Many people who have not studied science thin k that respiration and breathing mean the
same th ing.
In your group of three, think about the meanings of these two words. (Look at Topic 1.3
to remind yourse lf about breathing.) Think of a good way of explaining the differences
between respiration and breathing, to someone else.
Choose one of these methods to give your explanation:
•
making a poster
•
producing a slide presentation
•
giving an illustrated talk.
Decide how to share the tasks between you, and then work on your explanation.
Self assessment
How well did you do each of these things as you worked on this activity?
•
I made sure that I really understood the difference between breathing and respiration.
•
I helped to decide which method we would use to give our explanation.
•
I carried out my part of the task really well.
•
I helped others in my group to carry out their tasks.
•
I discussed what I was doing with the others in my group.
•
I think that our explanation helped other people to understand the difference
between breathing and respiration .
23
)
_ _ _ _ _ _1__
R_e_s_p_ir_a_ti_o_n_____________,)
In the activity, you had to work out for yourse lf how to
explain the difference between breathing and respiration.
Do you think this helped you to understand the difference
yourself? Or would it have been better just to be told the
difference by your teacher?
Why do you think that?
Summary checklist
□
I can explain that respiration is a chemical reaction that releases useful energy from glucose,
in a controlled way.
□
□
□
□
I can write the word equation for respiration.
24
I can state that respiration happens inside every living cell.
I can state that aerobic respiration uses oxygen, and happens inside mitochondria.
I can explain the difference between breathing and respiration.
)
1.5 Blood
> 1.5 Blood
In this topic you will:
•
learn about the structure of b lood
•
find out about the functions of red blood cells, white blood
cel ls and blood p lasma.
Getting started
Key words
With a partner, think about these questions.
antibodies
•
What do red b lood cells look like?
•
What is the function of a red b lood cell?
•
How do the features of red blood cell s help them to
perform this function?
blood plasma
oxyhaemoglobin
pathogens
red blood cells
white blood cells
Be ready to share your ideas.
0
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0
25
)
_ _ _ _ _ _1__
R_
e_s_p_ir_a_ti_o_n_____________,)
Delivering the requirements for
respiration in cells
You have seen that all of your cells need energy to stay alive. Each cell
gets its energy through a chemical reaction called respiration.
Aerobic respiration happens inside the mitochondria in the cells.
The reactants are glucose and oxygen:
glucose + oxygen ---+ carbon dioxide+ water
So, every cell in your body needs a good supply of glucose and oxygen,
and the carbon dioxide and water that the cell makes must be taken
away. The delivery and removal is done by the blood.
The blood moves around the body inside blood vessels. The heart pumps
constantly, to keep the blood moving.
What is blood?
Everyone knows that blood is a red liquid. But if you are able to
look at some blood through a microscope, you may get a surprise.
The photograph shows what you might see.
----------- This is the liquid part of the blood. This liquid
is called blood plasma. You can see that it is
not red at all. It is a very, very pale yellow.
Blood looks red because it contains a lot of
red blood cells, which float in this liquid. Most
of the cells in our blood are red blood cells. An
adult person has at least 20 trillion red blood
cells in their body. There are about five million
3
of them in every 1 cm of your blood.
These are called white blood cells. There are
not many of them, but some of them may be
quite a lot bigger than the red blood cells.
They don't look white in the photograph
because a stain has been added to the blood,
to make the cells show up more clearly.
The dark purple areas in these cells are their
nuclei. (Red blood cells don't have nuclei!)
Blood viewed t hrough a microscope
26
)
1.5 Blood
Questions
1
Look at the photograph on the previous page.
Approximately how many times more red blood cells
are there than white blood cells?
2
The photograph on the right was taken with a
powerful electron microscope.
What differences can you see between the red blood
cell and the white blood cell?
A red blood cell and a white blood cell
Plasma
Plasma is the liquid part of blood. It is mostly water. The red and
white blood cells are transported around the body in the blood plasma.
Plasma also has many other different substances dissolved in it.
For example, glucose, dissolved in blood plasma, is transported from
the digestive system to every cell.
You will remember that carbon dioxide is produced in every body cell,
by respiration. The carbon dioxide dissolves in blood plasma and is
carried away from the cells. The blood takes it to the lungs, where the
carbon dioxide diffuses out and is breathed out in your expired air.
Red blood cells
Stage 7, Topic 1.3 described how the structure of red blood cells is
related to their function. Now you are going to think about this in a
little bit more detail.
Red blood cells are very unusual cells. They do not have nuclei and
they do not have mitochondria. They are full of a red pigment
called haemoglobin. It is haemoglobin that makes blood look red.
The structure of a red blood cell is related to its function .
cell membrane
cytoplasm
• There is no nucleus, to make
more room for haemoglobin.
• The cytoplasm contains a red
pigment called haemoglobin,
which carries oxygen.
• There are no mitochondria in
the cytoplasm.
A red blood cell
27
)
______
1_R_e_s_p_ir_a_t_io_n_____________)
The haemoglobin helps the red blood cells to transport oxygen.
•
As the blood flows through the tiny capillaries next to the alveoli in
the lungs, oxygen from the air diffuses into the blood, and into the
red blood cells.
•
Inside the red blood cell, the oxygen combines with haemoglobin.
It forms a very bright red compound called oxyhaemoglobin.
•
As the blood continues on its journey around the body, it passes cells
that are respiring. The oxyhaemoglobin lets go of its oxygen and
gives it to the cells.
•
The blood, which has given away most of its oxygen, now travels
back to the lungs to collect some more.
This explains why red blood cells have haemoglobin - but why don't they
have nuclei or mitochondria? Scientists think that not having a nucleus
makes more space for haemoglobin. They also think that not having
mitochondria stops the red blood cells from using up all the oxygen for
themselves, instead of delivering it elsewhere.
alveolus in lungs
-c==s=~.
blood containing a
--~--,,, lot of oxygen flows
' ,, '-_ away from lungs
''
'
\ ''
' ' '\
'
\
'' ''
' '
,,;,_,
,,z
,;
,,
,.,,-
, ,'
,, ,,
,,, ,,,
,I ,'
, '
' ''
''
''
''
''
''
\
''
'' '''
'' ''
' '
' '
haemoglobin in
red blood cells
picks up oxygen
'
blood containing \ ~ ' ,,
a small amount of ',,~ ,
',, __ ',
oxygen flows away
haemoglobin in
red blood cells
from body cells
oxygen diffuses
into body cells
How oxygen is transported around t he body
Another way in which red blood cells are adapted for their function is
that they are quite a lot smaller than most cells in the body. Being so
28
)
'' '
,' ''
,, , ,,'
// ,/
/~,/
1.5 Blood
small helps them to get through very tiny blood capillaries. This means
they can get really close to the alveoli in the lungs, and to the respiring
cells in other parts of the body.
Quest ion
3
Explain why red blood cells might use up oxygen, if they have
mitochondria.
White blood cells
White blood cells are easy to distinguish from red blood cells. They
always have nuclei, which red blood cells do not have. Some kinds
of white blood cell - but not all - are larger than red blood cells.
Some bacteria and viruses can cause illness when they get into the body.
These bacteria and viruses are called pathogens. White blood cells help
to defend us against pathogens.
Some kinds of white blood cell can change their shape, and
push their cytoplasm out to make 'fingers' that can capture a
bacterium. The white blood cell then produces chemicals that
kill and digest the bacterium. This is called phagocytosis.
bacterium
white
blood cell
Other types of white blood cell produce chemicals that kill pathogens.
These chemicals are called antibodies. They are shown as little
Y-shapes on the diagram below. Different kinds of antibodies are
needed for each different kind of pathogen.
The antibodies stick onto the pathogen. Sometimes, they kill the
pathogen directly. Sometimes, they glue lots of the pathogens together
so that they cannot move. This makes it easy for other white blood cells
to capture and kill the pathogens.
1
Bacteria may get into the body.
Some kinds of of bacteria are
pathogens. They could make you ill.
\,\
, '.. ,
_
.i...
2
Some kinds of white
blood cell make chemicals
called antibodies.
The antibody molecules
stick to the bacteria.
Sometimes, the antibodies simply kill
the bacteria. Sometimes, they stick
them together so that other white
blood cells can come and kill them.
29
)
______
1_R_e_s_p_ir_at_i_o_n_ _ _ _ _ _ _ _ _ _ _ _)
Activity 1.5.1
Making a picture of blood
You are going to make a picture of some blood, as it might look if you saw it through
a microscope. Work as a pair, or in a small group.
You will need:
• a sheet of plain paper
• some red card
• some white card
• scissors
• glue
Method
1
Use the red card to make some red blood cells. Think about how many you need to make.
2
Use the white card to make some white blood cells. Use a pen or pencil to draw a
nucleus in each one. Think about how many you need to make.
3
Stick the red blood cells and white blood cells onto the white paper. The white paper
can represent the b lood plasma.
4
Write labels to stick onto the paper. Remember to label the b lood plasma.
Question
Copy and complete this table.
4
Component of blood
Appearance
Function
red b lood cell
white b lood cell
p lasma
Name three things that are transported in blood plasma.
5
Summary checklist
D I can describe what blood plasma is, and its function.
D I can explain how red blood cells, containing haemoglobin, transport oxygen.
D I can explain how white b lood cells help to protect us against pathogens.
30
)
--
Check your progress
1
The list includes some of the structures that air passes through, as it moves
from outside the body to the place where gas exchange happens.
Write the structures in the correct order.
bronchiole
2
bronchus
alveolus (air sac)
[2]
Tbe diagram shows an air sac and a blood capillary.
a
Copy the diagram. Label:
•
the blood capillary
•
the wall of the air sac.
b
Draw two red blood cells in the correct place on your diagram.
C
Draw an arrow to show the direction in which oxygen diffuses. Label
your arrow 0.
[1 ]
Draw an arrow to show the direction in which carbon dioxide diffuses.
Label your arrow C.
[1 ]
Describe how the red blood cells transport oxygen to all the cells in the body.
[2]
d
e
3
trachea
In each of these groups of statements, only one is correct.
Choose the correct statement, and write down its letter.
a
A
Every living cell respires.
B Only animal cells respire.
C Respiration uses up energy.
1 Respiration
b
A
Expired (breathed out) air contains only carbon dioxide.
B Expired air contains more carbon dioxide than inspired (breathed in) air.
C Expired air contains more oxygen than inspired air.
C
A
[11
Respiration means using your diaphragm to move air into the lungs.
B Respiration is the diffusion of gases between the air sacs and the blood.
C Respiration is a series of chemical reactions that releases useful energy
from glucose.
d
[11
A Muscles in the lungs contract to make air move into them.
B The diaphragm muscles contract to move air into the lungs.
C Muscles between the ribs pull them downwards when we breathe in.
4
[1]
The diagrams show two blood cells.
a
Copy the drawing of the red blood cell. Label the cell membrane and
cytoplasm.
[1]
b
Name two structures that most cells have, but that red blood cells do not have. [2]
c
The white blood cell kills pathogens by phagocytosis.
Describe how it does this.
[2]
Other kinds of white blood cell have a different way of killing pathogens.
Explain how they do this.
[3]
d
Project
Project: Helping white blood cells to protect us from pathogens
This project is about how scientific knowledge develops over time, and how scientific
discoveries can help people all over the world.
Background
Our white blood cells are amazing at keeping us safe from pathogens. Most of the time,
they manage to destroy the pathogens so that we recover quickly from an infection.
But there are some pathogens that white blood cells cannot destroy in time. The virus that
causes rabies is one of these. If the rabies virus gets into a person's body, the body needs
outside help in order to stop the virus spreading. Without treatment, most people die if
they are infected with the rabies virus.
Your task
You are going to work in a group to find out information about rabies, and how it can be
successfully treated. Each group will work on a different topic.
Choose one or two of these topics to research with your group. Also choose how you will
present your findings to others. You could make a poster, or give an illustrated talk.
Discovering what causes rabies
Who first discovered the cause of rabies, and when did they do this?
First vaccine for rabies
Who created the first vaccine
for rabies, and how did they
do this?
How rabies is transmitted
How can a person be infected
with rabies?
Preventing rabies
In which countries is rabies most
common? What can people in
these countries do to reduce
the risk of getting rabies?
Treatment for rabies
What should someone do if they
have been bitten by an animal
with rabies? How do rabies
vaccines help our white blood cells
to fight the virus?
33
)
Properties of
materials
> 2.1 Dissolving
In this topic you will:
•
use the scientific terms associated with dissolving, correctly
•
investigate the properties of solutions
•
practise measuring mass and volume
Getting started
Key words
With a partner:
conserved
•
explain the differences between an element, a compound
and a mixture
•
draw a diagram of the way particles are arranged in a liquid
•
share your answers with the class.
-
C
dissolving
opaque
solute
solution
solvent
transparent
•
•
•
•
..
..
2.1 Dissolving
What is a solution?
When you place a lump of sugar in water, the sugar seems gradua!Jy to
disappear. The sugar is dissolving. You are left with a colourless solution.
The substance that dissolves is called the solute. The substance that it
dissolves into is caUed the solvent.
A solution is a mixture. So, in our example, the colourless solution is a
mixture of sugar and water. Although the sugar seems to disappear, it is
still there. The sugar particles have simply spread out among the water
particles.
Sugar is the
solute.
Water is the
solvent.
When the sugar cube is
added to the water, t he
sugar starts to dissolve.
When the sugar has dissolved,
the sugar and water mixture
is the colourless solution.
The diagrams below show what happens to the sugar particles when the
cube dissolves.
1
The sugar crystal is visible
because it is made of lots
of groups of vibrating
particles that are tightly
packed together.
2
As the wat er particles vibrate and
slide past one another they bump
into the vibrating sugar particles.
The movement helps to separate
the sugar particles and they get
m ixed up with the water particles.
3
Eventually, the wat er particles
separate all the sugar
particles. The sugar particles
are no longer in groups and
are too small to be seen.
35
)
______
2_P_r_o_p_e_rt_i_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ _ _ _)
All solutions are transparent. This means you can see through them.
Transparent doesn't mean colourless. For example, if you dissolve a
coloured salt, such as copper sulfate, the solution formed is blue.
But you can still see through it. It is still transparent.
A liquid such as milk is not transparent. You cannot see through it.
It is opaque. Because of this, you can tell that milk is not a solution.
Copper sulfat e forms a solution. It is t ransparent.
M ilk is not a solution. You can tell this because it is opaque.
It is easy to confuse melting with dissolving. Remember: dissolving
needs two substances, a solute and a solvent.
Examples of dissolving
Examples of melting
Sugar (solute) in b lack tea
(so lvent)
Butter in a frying pan
Instant coffee (solute) in hot
water (solvent)
Ice cream on a warm day
Nail polish (solute) in nail polish
remover (solvent)
Cand le wax as the candle burns
36
)
2.1 Dissolving
Think like a scientist
top pan balance
Dissolving and mass
You will need:
• top pan balance
• salt
• stirring rod
• filter paper
• beaker of water
Method
1
Place the filter paper on the top pan balance.
Measure and record its mass.
2
Add about 20-25 g of salt. This is the solute.
Measure and record the mass of the salt.
3
Remove the paper and salt from the balance.
4
Place a beaker containing at least 100cm 3 of water on the top pan balance.
Measu re and record the mass of the water and the beaker together. The water
is the solvent.
5
Add the salt to the water. Stir until all the salt has dissolved. Measure the mass
of the beaker and salt solution.
beaker of at
least 100 cm 3
water
Questions
1
What was the mass of salt used?
2
What was the mass of the water and the beaker?
3
What was the mass of the solution and the beaker?
4
What does this tell you about the salt solution?
When salt is added to water and it dissolves, it has not disappeared.
The salt particles are still in the water. T he mass of the solution equals
the total mass of the solute and solvent. T his is true for any solution.
mass of solute + mass of solvent = mass of solution
No mass has been lost. The mass has been conserved.
37
)
______2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Questions
In a solution of sugar and water, which is the solvent and which
is the solute?
What is the difference between dissolving and melting?
What mass of salt solution is made when 9 g of salt is dissolved
in 50 g of water? Explain how you worked out your answer.
1
2
3
4
A green powder was placed into a beaker of water. After it was
stirred, the water looked cloudy and lumps of powder could still be
seen. Has a solution been formed? Explain your answer.
5
When measuring the volume of a liquid, what should you do in
order to make your measurement as accurate as possible?
Summary checklist
D I can use the terms 'solvent', 'solute' and 'solution' appropriately.
D I can use particle theory to explain some of the properties of solutions.
D I can measure mass and volume of liquids accurately.
38
)
2.2 Solutions and soulbility
> 2.2 Solutions and
solubility
In this topic you will:
•
make solutions of different concentrations
•
compare the number of solute particles in solutions
of different concentrations
•
investigate solubility
•
compare the solubility of various solutes
Getting started
Key words
You have one minute to think about the meanings of the words
solvent, solute and solution. You have one minute to discuss
them with a partner. Now write your meanings on different
pieces of paper. Share them with the class.
concentrated
f_:
dilute
insoluble
saturated
solubility
soluble
solution
39
)
______2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Solutions
A solution is made when a solute is dissolved in a solvent. More
particles of the solute are dissolved in a concentrated solution than in
a dilute solution.
A concentrated solution of sugar has a lot
of sugar part icles.
A d ilut e solution of sugar has fewer
sugar particles.
0
Think like a scientist
,-
Making different concentrations of a solution
You will need:
• safety glasses
• test tubes
• test tube rack.
• pipette
• 2 x measuring cylinders, suitable for measuring 10cm3
• strong solution of food dye
• beaker of water
Method
1
Carefully measure out 1Ocm 3 of the strong food dye solution.
When you have added about the correct volume you can use
the pipette to add or remove the fina l amount drop by drop, so
that your measurement is as accurate as possible.Place it in a
test tube and leave it in the test tube rack. This is solution A.
2
Carefu lly measure another 8 cm 3 of the strong food dye solution.
Pour it into a test tube.
3
Measure out 2cm3 water and add it to the food dye.
Leave it in the test tube rack. This is solution B.
40
)
2.2 Solutions and soulbility
Continued
4
5
Use the table below to make up food dye solutions C, D and E.
Place the solutions in the test tube rack, in order, from A-E.
Solution
Volume of strong food
dye solution/in cm
Volume of water/
incm
Total volume/
in cm
A
10
0
10
B
8
2
10
C
6
4
10
D
4
6
10
E
2
8
10
Look carefully at the solutions you have made.
Questions
1
What do you notice about the solutions?
2
How can you te ll which is the least concentrated?
3
If you repeated this task using a salt or sugar solution, would you
be able to identify the most and least concentrated solutions?
Explain your answer.
4
Why is it important to measure the food dye solution and the
water accurately?
5
If you only had a measuring cylinder that measured up to 100cm3 ,
would using these same volumes of copper sulfate and water
be accurate?
6
Compare the number of particles of food dye in the most
concentrated solution of food dye and the most dilute so lution.
Solubility
A solid that dissolves in a solvent such as water is said to be soluble.
Sodium chloride (common salt) and sugar are soluble.
A solid that will not dissolve in water is insoluble. Iron filings are
insoluble in water.
If you keep adding a soluble solid to a beaker of water, there comes
a point where no more of the solid will dissolve. You have made a
saturated solution.
41
)
_ _ _ _ _ _2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Some soluble substances are more soluble than others. If you have
100cm3 of water, you would be able to dissolve a lot of sodium chloride
in it, but only a tiny amount of lead chloride. Sodium chloride has
greater solubility than lead chloride.
Think like a scientist
Solubility in water
You will need:
• test tubes
• test tube rack
• measuring cylinder
• spatula
• a range of solutes such as sodium chloride, potassium sulfate and sugar
In this task you wi ll use various solutes and investigate their solubility in water.
You will use water at room temperature.
Method
1
Place a measured volume of water
in a number of test tubes. Use a
different test tube for each of
the solutes.
2
Add the first solute to the water.
Count how many spatulas of the
solute you can add until no more
will dissolve. After you add each
spatula of the solute shake or
stir the contents of the test
tube carefully.
3
Repeat for the other solutes.
4
Record your results in a table.
=
Questions
1
Which was the most soluble of the solutes you used?
2
Which was the least soluble of the solutes you used?
3
In this investigation you used the number of spatulas as a measure of the quantity
of solute added. Suggest another way of measuring the amount of so lute used, to
improve the accuracy of the results.
How can you ensure your results are as accurate as possible?
42
)
2.2 Solutions and soulbility
Comparing solubility
To compare the solubility of different solutes you must measure how
much of each solute will dissolve in a known amount of the solvent.
The table shows the solubility of different salts. It shows how much of
each salt can be dissolved when it is added to 100 g of water at 20 °C.
Solute
Solubility (measured in grams) of solute
in 100 g of the solvent at 20 °C
sodium ch loride
36
copper sulfate
32
calcium chloride
74
potassium ch lorate
7
lead chloride
1
Questions
1
What is a saturated solution?
2
How much copper sulfate will dissolve in 100 g water at 20 °C?
3
How much potassium chlorate would dissolve in 200 g water at 20 °C?
4
How much sodium chloride would dissolve in 50 g water at 20 °C?
5
Use the data in the table to draw a bar chart to show the solubility
of the various solutes in 100 g water at 20 °C
Temperature and solubility
Most solutes will dissolve more quickly and easily in hot water than in
cold water. Think about what happens to the particles when they have
more energy. The more energy the particles have, the more they vibrate
and move.
You can dissolve a greater mass of the solute in hot water than in the
same volume of cold water. In other words, as the temperature increases,
the solubility of most solutes also increases.
For example, if you have 100 g of water at 20 °C you can dissolve 204 g
of sugar in it. If you heat the water to 80 °C, you can dissolve 362 g of
sugar in it.
43
)
_ _ _ _ _2__
P_ro_p_e_rt_ie_s_o_f_m_a_te_r_ia_1s_ _ _ _ _ ___,)
Worked example
Question
204 g of sugar dissolves in l 00 g of water at 20 °C
a How much will dissolve in 200 g of water at 20 °C?
b How much sugar will dissolve in 50 g of water at 20 °C?
Answer
a 200 g of water is twice as much as 100 g, so twice as much sugar will dissolve 204 x 2 = 408 g
b In I 00 g water, 204 g sugar dissolves
In I g water, 204
100 g sugar dissolves = 2.04 g
In 50 g water, 2.04 x 50 g sugar dissolves= 102 g
Questions
6
How much sugar can be dissolved in 250 g of water at 20 °C?
7
How much more sugar can be dissolved if the 250 g of water
is at 80 °C?
Comparing the solubility of different salts
This table and the graph below show the solubility of three salts at
a range of temperatures. Look carefully at the graph and answer
the questions.
Temperature
in °C
Potassium nitrate in
grams per 100g of water
Sodium nitrate grams
per 100g of water
Copper sulfate in grams
per 100 g of water
0
14
73
13
10
21
81
15
20
32
88
17
30
45
96
20
40
63
105
30
~
so
84
114
35
C
60
108
124
40
70
136
134
47
80
168
148
56
·~
F
\\-
,~
,.._
~
.
l!d1
~
b
44
)
,
2.2 Solutions and soulbility
170
160
150
~
140
130
O'l
120
C:
oa w µ 1tr.a e
~ 110
I?
55\
l
C
,g
ulfat,
it iitl
"'3:
~ 100
0
~
£
90
-0
(II
>
0V,
80
.!:'.
70
-~
-0
...."'
r
V,
0
V,
V,
"'
~
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
Temperature in'C
Graph showing the solubility of three salts at a range of temperatures
Questions
8
What is the general trend for the solubility of all three salts?
9
What is the solubility of potassium nitrate a 45 °C?
10 Which of these three salts is most soluble at I0°C?
11 Which salt is the most soluble at 80°C?
45
)
_ _ _ _ _ _2__
P_ro_p_e_rt_ie_s_o_f_m_a_t_e_r_ia_1_s_ _ _ _ _ _ __,)
Other solvents
Water is not the only solvent. Some substances that are insoluble in
water will dissolve in other solvents. For example, some types of oil
paint are not soluble in water. So if you need to clean your brushes after
you've used oil paint, you will need to use a solvent that the paint will
dissolve in, such as methanol ( methylated spirits).
These paint brushes are being cleaned in jars of methyl ated
spirit.
Nail polish does not dissolve in wat er but dissolves in
nail po lish remover, most nail po lish remover contains t he
solvent p ro panone (acetone).
-
Summary checklist
D I can describe how to make solutions of different concentrations.
D I can compare the number of solute particles in solutions of different concentrations.
D I can carry out an investigation safely.
D I can compare the solubility of various solutes.
46
)
(U
2.3 Planning a solubility investigation
> 2.3 Planning a solubility
investigation
In this topic you wil l:
•
plan an investigation, considering all the variables
•
carry out an investigation
Getting started
Discuss with a partner the difference between accurate results
and reliable results. Share your ideas with the class.
control variables
dependent
variable
independent
variable
interval
range
variables
______2__
P_
ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Dissolving salt in water
These students are discussing how they will investigate how temperature
affects the amount of salt that will dissolve in water. They are trying to
think of all the different things that could affect the results. These are
the variables.
Ouestions
1
Which variables have the students identified?
2
How do you think the volume of water will affect the results if it is
not kept the same? Explain your answer.
The students carry out the experiment. They decide to count the number
of spatulas of salt (sodium chloride) that will dissolve in 50cm3 of water.
They will repeat the experiment at different temperatures from 20 °C to
80°C.
The variable they change is the temperature of the water. They will
count the number of spatulas of salt that will dissolve. This is the
variable that depends on the temperature of the water.
The volume of water is the variable that the students keep the same, to
ensure that the test is fair.
The variable you change is called the indep(..'ndent variable. The variable
you measure is called the dependent variable. The variables you keep the
same are the control variables.
When you plot a graph of your results, the independent variable always
goes along the horizontal axis. The dependent variable always goes up
the vertical axis.
48 )
2.3 Planning a solubility investigation
spatula
salt
~
The volume of water is kept t he same.
The temperature is changed.
The number of spat ulas used
is measured.
Questions
3
Which variable is the independent variable in the students'
investigation?
4
Which variable is a control variable in the students' investigation?
Is there any other variable that needs to be controlled? (Hint: think
about the spatula.)
5
Which is the dependent variable in this investigation?
6
What would the label be on the vertical axis of a graph of the results
of this investigation?
Think like a scientist
---
...C
Plan and carry out an investigation into the effect of water temperature on the
amount of sodium chloride {common salt} that will dissolve in it
Part 1: Planning the investigation
In a group of two or three, discuss the plan for your investigation.
You need to consider the variables, risk assessments, equipment and method.
Discuss these questions.
•
What volume of water you will use?
•
How you will change the temperature of the water and how you will keep it at that
temperature while you add the sodium chloride?
•
What range of temperatures you will use? (The highest and lowest temperatures
you will use.) Remember to be practical about t h is.
•
What interval between temperatures will you use? (Will you use gaps of 10 degrees
between temperatures, or 5 degrees?)
•
What will you do to ensure you are safe while carrying out your investigation?
49
)
_ _ _ _ _ _2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Continued
•
What equipment will you need?
•
What method will you use?
You need to prepare a table to use for your results. Think about how many columns
you will need. What headings will you use? What units will you use? How many readings
wi ll you take? Wi ll you repeat your tests?
Once you have discussed your plan with your teacher, you may need to
change a few things.
Make sure you have a ful l plan written, including a step-by-step method,
before you carry out the investigation.
Have you considered everything you need for your investigation?
How can you improve your planning?
Think like a scientist
Plan and carry out an investigation into the effect of water temperature on the
amount of sodium chloride (common salt) that will dissolve in it
0
Q
Part 2: Carrying out the investigation
Collect the equipment that you chose in your p lan.
Make sure you have your step-by-step method to follow.
C
Questions
1
Plot an appropriate graph.
2
Explain what you have found out.
3
Would you expect similar results if you used another salt, such as copper
sulfate or lead chloride?
Summary checklist
D I can identify different types of variables.
D I can plan an investigation.
D I can carry out an investigation safely.
50
)
0
2.4 Paper chromatography
> 2.4 Paper chromatography
In this t o pic you wil l:
•
use paper chromatography to separate dissolved substances
•
interpret chromatograms
•
use scientific language accurately
Getting started
Key words
Draw diagrams to show the ways you could separate mixtures
that involve solutions. Check your ideas with a partner.
chromatogram
paper
chromatography
permanent
solvent front
51
)
______2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Colours in ink
Black coloured ink looks as if it is just one colour - black. In fact, it is
a mixture of different coloured inks. You can separate out the coloured
inks by using a technique called paper chromatography.
Special paper, a bit like filter paper, is used.
Look at the photograph. A small drop of black
ink has been placed on the paper. The water
in the beaker has soaked up into the paper.
As the water moves up the paper, the different
coloured inks that make black ink separate out.
The resulting image on the paper is called
a chromatogram.
The coloured inks separate because the water
dissolves them. Water is the solvent. As the
water moves up the paper, it carries the ink
particles with it. The different kinds of ink particles are carried different
distances before they are left behind on the paper. This is because not all
the ink particles have the same solubility. The more soluble the ink, the
further its particles are carried.
In the photo, you can see the different coloured inks that make up the ink
in three different coloured pens - green, black, and red.
Some ink is not soluble in water, such as the ink in permanent marker
pens. To separate out the colours in these inks, you would need to use a
different solvent, such as alcohol.
52 )
2.4 Paper chromatography
Think like a scientist
Separating the colours in ink
You will need:
• chromatog raphy paper (or filter paper)
• glass rod or wooden spill
• beaker
• water
• pencil and ruler
• ink (pipette needed if it is liquid ink)or a pen
• various other inks and/or food dyes
Method
1
Take a strip of chromatography paper. Draw a pencil line about 1 cm from the end.
2
Place a spot of ink on the pencil line. The spot should be as small as possible.
3
Dry the spot and then add a little more ink.
4
ace about 2 cm depth of water in a beaker.
5
Hang the paper over a glass rod, penci l or wooden spill so that the end with the ink
spot is just in the water. Make sure the ink spot stays above the level of the water.
6
Watch what happens as the water moves up the strip of paper.
\/
•
~
..._
.....
•_:,
7
Remove the strip of paper before the water reaches the top.
You need to be careful as the wet paper can tear easily.
8
Allow the strip to dry and then stick it in your book. This is your chromatogram.
You can try this with all sorts of co loured liquids. Different inks and food dyes,
especially from sweets or fruit syrup, are very good. You could also try this with
permanent marker pens that have ink that is not soluble in water.
Questions
1
Why did you use a line drawn in pencil on the paper?
2
Why was it important not to let the ink spot go under the water?
3
Why was it important to remove the strip of paper before the water level
reached the end of the strip?
4
Describe your results.
53
)
______2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Did you have any difficulties carrying out this practical work?
How did you overcome them?
How could you improve the way you carried out this practical task
When comparing different substances, a scientist may use a large piece
of chromatography paper and place spots of different items alongside
each other. The scientist will allow the solvent to move up through all
the samples at the same time. To do this, the paper needs to be placed
in a large chromatography tank.
The chromatogram shown here has been produced using this technique.
It shows the colours in a number of different felt tip pens.
•
1k
0
Scientists use chromatography to study the dyes used in food. Some
food dyes contain only one substance; they are a pure substance. Other
dyes contain a mixture of substances. It is important to know exactly
what is being used when our food is processed - we need to know if any
substances could be a health risk; for example, they could be toxic or
cause allergic reactions.
Questions
The drawing of a chromatograph shows the results for some food dyes.
1
Which food dyes are pure substances?
2
Which food dye is not a pure substance?
54
)
2.4 Paper chromatography
3
Which coloured substance in the food dyes is the most soluble?
4
Which coloured substance in the food dyes is the least soluble?
blue
I
I
brown
yellow
5
The chromatogram for Sunny Red shows four separate substances.
Are any not permitted? If so, which?
6
T he scientist decides to run the test again. Why does she do that?
7
Which of the substances in Sunny Red is the most soluble?
Give a reason for your answer
Public health scientists may also use chromatography
to check that the colourings being used in products
such as hair dye o r the ink in pens are not harmful.
To do this they compare chromatograms taken from
a solution of the food, hair dye or ink and those of
the colourings that are permitted.
The diagrams in below show a chromatogram from
a hair dye called Sunny Red and a chromatogram
showing all the permitted dyes.
D
C
B
t
A
,.
•
chromatogram
from Sunny Red
'
chromatogram of permitted dyes
~
Activity 2.4.1
Using the correct words
This unit uses a number of words that look and sound sim il ar. For example: solute,
solvent, solution; chromatography, chromatogram; dissolve, dilute. Your task is to make
up a game to help you learn them. You could make a set of cards with the words written
on them, and another set of cards with the meanings written on them .
Think how you could use these to make a game. Your game can be for any number of
p layers, you decide how many you want to play.
55
)
_ _ _ _ _ _2_P_r_o_p_e_rt_ie_s_o_f_m_at_e_r_ia_1s________)
How do you learn new words and terms? Does a game help?
Which is the most effective way of learning for you?
Think like a scientist
Is the green colour in plant leaves pure?
You will need:
• fresh plant material such as spinach
• pestle and mortar
• chromatography paper
• pencil
• beaker
• ethanol
• pipette
• glass rod or spill
Safety
When using ethanol, make su re you are in a well-ventilated room
and there are no heat sources close to you .
Method
Add a handful of spinach and a few drops of ethanol into
the mortar. Use the pestle to crush the spinach and ethanol
together. Let it stand for about 10 minutes to leave t ime for
the green pigment to dissolve in the ethanol.
1
2
Prepare the chromatography paper with a pencil line and a
cross, about 1 cm from the end.
3
Use a pipette to load some of the green liquid from the mortar
onto the cross. Allow the spot to dry before adding more of
the liquid.
4
Place the chromatography paper over a glass rod or pencil.
Hang it in a beaker containing some ethanol, so that the
pencil line is just above the ethanol.
5
Watch carefully and remove the chromatography paper before
the ethanol reaches the top of the paper. The point that the
solvent reaches is called the solvent front.
0
mortar
Allow the chromatogram to dry and then stick it in your book.
Questions
1
Why was ethanol used in this investigation and not water?
2
Is the green pigment in plants pure? What is your evidence for this?
56
)
E
0
2.4 Paper chromatography
Did you have any difficulties carrying out this practical work?
How did you overcome them?
How could you improve the way you carried out this practical task?
Summary checklist
0 I can describe how to use chromatography to carry out a practica l task to separate
d issolved substances.
D I can explain what the results of a chromatograph show.
D I can use scientific language accurately.
2
Propert ies of materials
Check your progress
2.1 Copy and complete these sentences. Use the words from the list.
You may use each word once, more than once or not at all.
solvent
mixture
solution
mass
temperature
suhu
saturated
dissolve
volume
insoluble
A solute is a solid that ... in a liquid. The liquid it dissolves into is called a ... .
Together they make a ... A solid that does not dissolve in a liquid is called ... .
The solubility of a solid measures how much of a solute will dissolve.
When you measure the solubility of a solute you must use the same ...
and type of solvent at a given ....
[6]
2.2 The table below gives the colours and solubility in water of four compounds.
Name
Colour
Solubility
sodium chloride
white
soluble
zinc carbonate
white
insoluble
iron sulfate
green
soluble
copper carbonate
green
insoluble
The compounds were added to separate beakers of water. There was enough
water to dissolve the soluble compounds completely. The contents of each
beaker were filtered.
One of the compounds left a white solid in the filter paper.
What is the name of this compound?
[1]
b
What is the co.l our of the filtrate from this beaker?
[1]
c
Describe how you could obtain pure crystals of iron sulfate from
a mixture of copper carbonate and iron sulfate.
[3]
a
2.3 Some students have been investigating the mass of copper sulfate that can
be dissolved in water at different temperatures. They added copper sulfate
until no more would dissolve and they carefully measured the mass of
copper sulfate they added. Here are their results.
Temperature of water in °C
20
30
40
50
60
70
80
Mass of copper sulfate dissolved in g
22
24
28
32
30
46
58
What name is given to a solution when no more of the solute can be
dissolved in it?
[11
b
What range of temperatures did the students use?
[11
c
What interval did they use for the temperatures?
[11
d
Name a variable the students should keep the same.
[1 1
e
Which is the independent variable?
[1 ]
a
Here is a graph of the results.
20-t:t!:t:::::!::t!:!:~!:t!::!::;::!::t::!+J!::!:!j::!:t!~:!::!::!::::.:!:t:t:::t:l=!:!::t:!:!::!::!:!jtl::!::J:::!:!:!::::::!:!::::::l
20
30
40
so
60
70
80
Temperature of water in ,C
f
Identify any results that do not fit the pattern.
[1 1
g
What conclusions can the students draw about their results?
[11
______2__
P_ro_p_e_r_ti_e_s_o_f_m_a_t_e_r_ia_1s_ _ _ _ _ ____,)
Project: The secret formula
This project is to show how scientists work together and share their ideas.
In this task, just like research scientists, you can only use the information
available and make deductions. As you share your ideas, you will think
about the information in different ways and then develop a theory and
suggest more investigations.
You will need:
• 4 x black pens
• a solution of the ink from the notes
Professor Sneeze has been working on a new medicine that will protect
people from coughs and co lds. If this medicine works it will save a lot of
people from feeling ill and taking time off work or school. It w ill also make
him famous and make a lot of money for the university.
Unfortunately, news that he has produced the medicine has reached some
people who want to steal the formu la, sell it to a company that will make
the medicine and make themselves rich.
While he is working in his laboratory, a note is delivered to Professor
Sneeze asking him to meet Professor Clean in her laboratory at
as she
has an interesting experiment that will finish at that time and may help
him in his work. Just before
he goes off to Professor Clean's laboratory.
When he arrives, Professor Clean is p leased to see him but has no idea
why he has come. She did not send the note.
t>ear- -Pr-ofessor- Snee3e,
I have an experiment. due lo finish lodaj. 1 think_ jOU will b e ver-j interested lo
see the results as t.hej maj help j0U -lo tmpr-ove -lhe wa j jOUr- new medicine can
b e pr oduced. -Please come t o mj lab or-ator-j at 11 .00am when the exper iment will
have finished and we can discuss -lhe r esults .
Best. wishes,
By the time Professor Sneeze gets back to his laboratory, the equipment
has been damaged and the formula has been stolen.
60
)
Project
Continued
Your t ask
Your group are going to help the professor try to find out who wrote
the note. Ink from the note has been dissolved in water and given to
you as a solution. Choose the equipment you will need and produce
a chromatogram to show the different components in the ink.
The professor has borrowed pens from the four most likely suspects.
Doctor Price: pen A; Doctor May: pen B; Doctor Burns: pen C and
Professor Green: pen D.
Your job is to test the ink from all four pens to identify which pen was
used to write the note.
In your group, discuss the these questions.
•
Who do you think wrote the note? Explain why you think that.
•
Explain how you produce a chromatogram.
•
What precautions must you take?
•
Is this enough evidence to be sure you have the person who has
the formula?
•
What other evidence would you look for?
Present your evidence to the class.
61
)
Forces and energy
> 3.1 Forces and motion
In this topic you will:
•
understand what 1s meant by balanced and unbalanced forces
•
describe the effects of balanced forces on motion
•
describe the effects of unbalanced forces on motion
0
Getting started
Key words
Work in groups to discuss answers to these questions.
analogy
balanced
change direction
direction
force
opposite
1
What is the unit of force?
2
How are forces shown on diagrams?
3
One or more forces always act on any object on Earth. Is this true?
slow down
speed up
unbalanced
3.1 Forces and motion
Balanced or unbalanced?
Look at any object that is not moving.
You may think that if an object is not moving, no
forces are acting to push, pull or twist it. This is not
true.
Look at the rock in the picture. The force of gravity
is pulling it toward the centre of the Ea11h. This force
is called its weight. The rock does not move toward
the centre of the Earth because the ground is pushing
up on the rock. This force is the contact force.
contact force
These two forces are balanced. This means the forces
are equal in size and opposite in direction.
rock
There could be more than two forces acting on
the rock.
Imagine the wind is blowing. The wind will push
the rock from one side.
Why does the rock not move sideways? The pushing
force from the wind is balanced by friction between
the rock and the ground.
These forces can be shown in a force diagrams. In a
force diagram, the arrows show the size and direction
of each force. The longer the arrow, the bigger
the force. So, when you draw a force diagram with
balanced forces, make sure the arrows are the same
length and point in opposite directions.
Starting to move
weight
The force d iagram shows the balanced forces acting
on t he rock.
wind
The forces acting on t he rock when t he wind
is b lowing.
Imagine the rock is now pushed with a much larger
force than the wind, such as a large vehicle.
When the vehicle pushes on the rock, the pushing
force will be larger than friction.
contact force
push from
large vehicle
The forces are no longer balanced and t he rock
will start to move.
63
)
______
3_F_o_r_ce_s_a_n_d_e_n_e_r_9_Y__________)
The rock will now move because the sideways forces are not balanced.
This can be shown on the force diagram.
The rock will now start to move in the direction of the larger
sideways force.
The rock will not move up or down because the forces acting up and
down are still balanced.
Slowing down
Unbalanced or unequal forces can also make moving objects slow down.
A parachute makes a falling object slow down.
When an object is falling quickly, the parachute causes a force of air
resistance that is larger than the weight of the object.
These forces can be shown in a force diagram.
air resistance
weight
weight
When the parachute first opens, the forces
are unbalanced. This unbalanced force
makes the object slow down.
When the object slows, the air resistance
decreases, so the forces become balanced
again. Then the object falls at a constant
speed.
This force diagram shows the object falling
at a constant speed.
64
>
3.1 Forces and motion
Changing direction
Unbalanced forces can also make objects change direction.
This tennis ball will change direction because of an unbalanced force.
When the bal1 contacts the tennis racket, the bal1 pushes on the tennis
racket. To make the ball go back in the opposite direction, the hitting
force must be larger than the force from the ball.
This can be shown in a force diagram.
•
tennis racket
hitting force on the ball
force from the ball
on the tennis racket
The tennis ball will change direction because of an unbalanced force.
Stage 7, Topic 3.3 described planets orbiting the
Sun due to the force of gravity.
The force of gravity on a planet is a constant,
unbalanced force.
When an object moves in a circle, its direction is
always changing. A constant unbalanced force is
needed to keep an object moving in a circle.
direction of
force
from the Sun's
gravity
Q sun
65
)
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Summary
•
When forces are equal in size and opposite in direction, the forces
are balanced.
•
Balanced forces cause no change in movement.
•
When forces are not equal in size and/or act in directions that are
not opposite, the forces are unbalanced.
•
Unbalanced forces cause change in movement: speeding up, slowing
down or changing direction.
Size of forces
Direction of forces
Balanced or
unbalanced
Change in movement
Equal
Opposite
Balanced
None
Equal
Not opposite
Unbalanced
Change of d irection
Not equal
Opposite
Unbalanced
Increase or speed
Unbalanced
Increase or decrease
speed and change
of direction
Not equal
Not opposite
Questions
1
a
Describe what is meant by 'balanced forces'.
b A box is on the floor. The box is not moving.
D raw a labelled force diagram to show all the forces acting
on the box.
ii
2
Amal pushes the box sideways. The box does not move.
Draw another labelled force diagram to show all the forces
acting on the box when Amal is pushing.
A tug of war is a game played by two teams of people, each pulling
on the same rope. The team that pulls the rope to their side wins.
The picture shows a tug of war. The teams in this game are called
Team A and Team B.
66
)
r-1
)
r=
3.1 Forces and motion
Both Team A and Team B are pulling on the rope.
The rope is not moving.
Use ideas about forces to answer these questions.
a
Explain why the rope is not moving.
b The rope starts to move towards Team B. Give two changes that
could make the rope move towards team B.
3
The diagram shows the forces on an
aeroplane in the air.
a
lih
Explain why this aeroplane is:
flying at a constant speed
thrust
weight
ii
not getting higher or lower.
b Name the force that should increase to make the aeroplane:
go faster
c
go higher or 'lift'.
Name the force that should decrease to make the aeroplane:
go lower
4
ii
ii
go faster.
The picture shows a toy train moving around a circular track.
The locomotive contains an electric motor that drives the train.
The train moves in a circle at a constant speed.
Give the letter of the arrow that shows the direction of:
a
the driving force of the train
b
the force of friction on the locomotive
c
the force that keeps the train moving in a circle.
67
)
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Activity 3. 1.1
Balanced or unbalanced forces?
On a large piece of paper, draw a table with two columns: one for balanced forces and
one for unbalanced forces.
Put each of these situations into the correct column, according to the forces that are acting.
The situations are:
•
a motorcycle going around a corner
•
a boy on a skateboard slowing down
•
a bowling ball rolling at constant speed in a straight line
•
a girl on a swing getting faster
•
a computer sitting on a desk
•
a helicopter going straight upwards at a constant speed
•
a coconut falling from a tree and getting faster.
How did you decide which situations had balanced forces and which
had unbalanced forces?
0
Did your strategy work?
..c
Could you use this strategy again, or would you change it?
S;
Think like a scientist
Measuring balanced and unbalanced forces
In this investigation, you wi ll investigate the effects of balanced and unbalanced forces.
Work in pairs.
You will need:
• two force meters
• piece of string
• coloured tape
• scissors
'J
Set up the equipment as shown in the diagram.
newton meter
string
coloured tape
coloured tape fixed to desk
68 )
newton meter
3.1 Forces and motion
Continued
Method
1
Each person in the pair holds one newton meter. The string should be tight.
The coloured tape on the string should be lined up with the coloured tape
on the desk.
2
Each person pulls with an equal force, for example,
Questions
1
What directions must you both pull to keep the pieces of co loured tape lined up?
2
Both people increase the pulling force to, for example,
Explain why the string does not move, even when the force is increased.Continued
3
One person decreases their force by . If the force was then decrease
the force to .
a Describe what happens to the string.
b Use a force diagram to explain what happens to the string.
4
Now make the difference between the forces larger, for example the difference
is now or .
How does the difference between the sizes of the forces affect the movement
of the string?
5
Explain why the two newton meters do not have to be the same.
6
This investigation is an analogy of a tug of war. That means the investigation
can be compared with a tug of war.
State what is represented by the newton meters in this analogy.
Self-assessment
Decide how confident you are about each of these statements.
Give yourself 5 if you are very confident and 1 if you are not confident at all.
•
I understand what balanced forces are.
•
I can d raw force diagrams to show balanced forces.
•
I can d raw force diagrams to show unbalanced forces.
•
I can predict some things that can happen when forces are unbalanced.
•
I understand that there can be forces acting on an object even when it is not moving.
69
)
_ _ _ _ _ _3__
F_o_rc_e_s_a_n_d_e_n_e_r_9_Y__________,)
Summary checklist
D I can describe what is meant by balanced forces in terms of size and direction.
D I can understand that forces can be acting on an object t hat is not moving.
D I can recognise when forces are unbalanced.
D I can list some of the effects of unba lanced forces.
3.2 Speed
> 3.2 Speed
In this topic you will:
•
understand what is meant by speed
•
learn about the unit of speed
•
be able to calculate speed
--------
Getting started
Key words
Work in groups to discuss answers to these questions.
average speed
calculate
constant
1
What are the speed limits for cars where you live?
2
Signs showing speed limits usually do not have units.
What are the units used for speeds of cars?
Units of speed
There are many different units of speed. Different units are sometimes
used in different countries and for different things. For example, the
speed of ships is often measured in knots, whereas aeroplanes often use
Mach. Some countries have road speed limits in kilometres per hour,
whereas some countries use miles per hour.
mis
metres
per
second
speed
_ _ _ _ _ _3__
Fo
_ rc_e_s_a_n_d_e_n_e_r_9_
Y_ _ _ _ _ _ _ ___,)
So, to avoid confusion, scientists use standard units for measurement in
all countries.
The standard unit for speed is metres per second.
The word per means 'in each'. Therefore, metres per second means the
number of metres travelled in each second. For example, a horse running
with a speed of 15 metres per second means the horse travels a distance
of 15 metres in each second.
Metres per second is written as mis.
Calculating speed
The way you calculate speed is linked to the unit metres per second, mis.
For example, think of a bus that travels a distance of 100 min a time of 20s.
The bus has travelled 100 m in 20 s, so how many metres does it travel in
each 1 s?
number of metres travelled in each second = total distanc~ travelled
total time
number of metres travelled in each second = speed, so
s eed = total distan~ travelled
p
total t1me
lQOm
-_ -
20s
= 5m/s
You can summarise this equation for speed as:
speed = dis~ance
time
Note: the term alerage speed is sometimes used because the speed of
an object during a journey is not always constant. Constant means not
changing. Average speed is calculated in exactly the same way as speed.
The equation for speed can be used in a formula triangle. This means
you can also use the equation to calculate:
•
the distance travelled, if you know the speed and the time taken
•
the time taken, if you know the speed and the distance travelled.
72
>
3.2 Speed
distance
speed
time
speed
speed =
distance
.
time
.
distance
t1me = - speed
time
distance = speed x time
A formula triangle
Worked example
Question
Q uestion
Marcus rides his bicycle at a speed of 4 m/s
for 60 s. How far does he go in this time?
Sofia is in a car travelling at a speed of 35m/s.
How long will the car take to travel 2100m?
Answer
Answer
distance = speed x time
time = distance
speed
= 4 X 60
_ 2100
35
- -
= 240m
= 60s
T he worked examples above both use metres, seconds and metres per
second. Sometimes, the values are given in different units. So, for example,
if you have a distance in km and a time in hours, the equation will give you
a speed in km/h as you are dividing a distance in km by a time in hours.
Worked example
Question
An aeroplane travels
in a ti me of 5 hours. What is the speed of the aeroplane in km/h?
Answer
time = distance
speed
_ 2500km
5 hours
= 500km/h
73
)
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Howeve1; unless you are told otherwise, always work in metres, seconds and
metres per second. Remember, in calculations, always:
•
show the steps you used in working out the answer
•
include the correct units with the answer.
Questions
1
a
Write an equation for speed, when you know the distance
travelled and the time taken.
b
Write down the standard scientific unit of speed.
c
Write an equation for distance travelled, when you know the
speed and the time taken.
d Write an equation for time taken, when you know the speed
and the distance.
In each calculation question that follows, show your working and give
the unit with your answer.
2
a
An Olympic sprinter completes the 100 m race in a time of 10 s.
Calculate the average speed of the sprinter.
b Explain why this value is an average speed.
3
A car travels a distance of 210 m in a time of 6 s.
a
Calculate the speed of the car in mis.
b Calculate the distance, in m, travelled by the car in 14s.
4
c
Calculate the time taken, in s, for the car to travel a distance
of 1925m
a
An aeroplane flies between two cities that are 8100 km apart.
The aeroplane takes 9 hours to complete the journey.
Calculate the average speed of the aeroplane, in km/h.
b A different aeroplane can fly at 800 km/h. Calculate the
distance, in km, that this aeroplane could fly in 6 hours.
c
Another aeroplane can fly at 950 km/h. Calculate the time taken,
in hours, for this aeroplane to travel a distance of 7125 km.
5
Anna sees a worm on the grass. Anna sees the same worm 2 hours
later. The worm has moved a distance of 3 m in that time. Calculate
the average speed of the worm, in metres per hour.
74
)
3.2 Speed
Activity 3.2.1
Speed, distance and time
Use a map or internet search engine to find the distances between some places
near to where you live.
You should include:
•
some shorter distances, such as from home to school
•
some longer distances, such as between cities.
The table gives some typical speeds for different methods of travel.
Method of travel
Typical speed in m/s
walking
2
cycling
7
10
12
20
30
35
200
horse riding
bus
small motorcycle
car
train
aeroplane
Use the information in the table to calculate the times taken for your different distances.
For each distance, choose some of the most appropriate methods of travel.
\,
Think like a scientist
Calculating speed
In this investigation, you will make measurements to calculate the speed of an object.
Work in groups of three or four.
,
i
You will need:
• ramp
• tennis ball
• smooth level surface
• 2 metre rules
• colou red tape
)
• books
• stopwatch
75
)
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Continued
Method
Set up the equipment as shown in the diagram.
coloured tape
1
Use coloured tape to fix the bottom of the ramp to the desk or floor.
2
Fix some coloured tape
3
Fix some coloured tape near the top of the ramp to mark where you will
release the object.
4
Measure the height from the desk or floor up to the position where you
will release the object.
5
Re lease the object and measure the time the object takes to move between
the two pieces of coloured tape on the desk or floor.
6
Repeat this two more times and calculate the average time to travel between
the two pieces of tape .
7
Do this for a range of different heights.
from the end of the ramp.
Results and questions
1
Record your results in a table.
2
Use your results to calculate the speed of the object between the two pieces
of tape. Add another column to your table, or draw a new table, to include
the speed. Remember to put the unit of speed in the column header.
3
Plot a line graph of the results. Put height on the hoizontal axis and speed on
the vertica l axis. Include the units on each axis.
4
What is:
a
the independent variable in this investigation
b the dependent variable in this investigation?
5
State two variables that were controlled in this investigation.
6
Explain why each measurement is repeated. Give two reasons.
7
Describe the trend in your results.
76
)
3.2 Speed
Continued
Self-assessment
Decide how well you:
•
made measurements
•
recorded results in a table
•
drew the graph of the results.
Choose one thing that you could do better next time.
How will you do this better next time? What will you change?
D I know and can use the equation that links speed, distance and time.
D I can use the equation to calculate speed, given distance and time.
D I can use the equation to calculate distance, given speed and time.
D I can use the equation to calculate time, given distance and speed.
D I know that standard units are metres, seconds and metres per second.
D I can calculate speeds using different units.
_ _ _ _ _ _3__
Fo
_ rc_e_s_a_n_d_e_n_e_r_9_
Y_ _ _ _ _ _ _ ___,)
> 3.3 Describing movement
In this topic you will:
•
learn how to use graphs to describe movement
•
understand what a distance-time graph shows
•
learn to draw a distance-time graph
--------
Getting started
Key words
Work in groups to discuss the answer to this question.
at rest
Imagine you are standing on a path.
You start walking at a constant speed.
What wou ld a line graph look like if you plotted the distance you
had walked on the vertical axis and time on the horizontal axis?
distance-time
graphs
safety precautions
sketch
stationary
3.3 Describing movement
Distance-time graphs
Scientists use graphs to describe how two variables are related.
We can use graphs to describe the movement of an object.
One way to do this is to plot distance travelled on the vertical axis and
time on the horizontal axis.
A graph like this is called a distance- time graph.
Graphs are more useful than words for describing movement because:
•
•
•
•
it is easier to see trends and patterns
you can read any value of distance or time during the journey,
from the graph
other values, such as speed, can be calculated from a graph
information about the whole journey can be seen easily.
This is a distance- time graph. It shows the journey of a car from a
starting position A to a destination, C. The car then returns to its
starting position.
2
3
4
Distance
A
A1F--- - - - -=----- - - ---=--- - - - - ------+
Time
Now take a closer look at what the graph shows in each of the four
sections. These sections are in different colours so you can see
them clearly.
1
2
At the starting position, A, the object has travelled zero distance.
The car travels at a constant speed away from the starting position
to point B. When moving at constant speed, the car travels the
same distance in each second. The distance from the start increases
with time. The distance-time graph show this as a straight, upward
sloping line.
The car stops at B. It is stationary. Stationary means not moving,
with a speed of zero. You can also use the term at rest to mean
stationary. The distance of the car from the start position does
not change when the object is stationary, but time still passes.
The distance-time graph shows a straight line that is horizontal.
79
)
_ _ _ _ _ _3__
F_o_rc_e_s_a_n_d_e_n_e_r_9_Y__________,)
3
The car starts again and moves at a constant speed to its destination,
point C. It moves faster than when it travelled between A and B,
meaning it travels a greater distance each second. So, the distance-time
graph show this as a steeper straight, upward sloping line.
4
From point C, the car travels at a constant speed back to the
starting position, A. The distance of the object from the start will
decrease with time. The distance- time graph shows this as a straight,
downward sloping line.
The distance- time graph for the car journey was a sketch. If you draw
a sketch graph you do not have to put numbers on your graph axes.
Sometimes, distance-time graphs have values on the axes. This means
you can use the graph to make calculations. Read the distance from the
ve11ical axis, and the time from the horizontal axis. Then use the equation:
speed :::: dis!ance
time
Worked example
Question
This distance- time graph shows a short train journey between two stations, P and R,
that are 2000 m apart.
•
The train leaves station Pat time 0.
•
The train takes 200s to travel from P to R.
•
The train stops at station R for 140s.
•
The train then travels back to station P in a time of 100 s.
2500
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Time ins
e At what speed does the train travel from station P to station R?
f
80 )
-1-
What is the speed of the train on the way back from station R to station P?
500
3.3 Describing movement
Continued
Answer
a The distance is 2000m and the time taken is 200 s.
speed = dis~ance
tune
_ 2000
- 200
= l0m/s
b The distance is 2000 m and the time taken is l 00 s.
speed = dis~ance
time
_ 2000
- 100
= 20m/s
Questions
1
2
a
Sketch a distance- time graph for an object moving at a constant
speed away from a starting position.
b
On the same graph, sketch another line to show another object
moving faster, away from the same starting position. Label this
line 'faster'.
c
On the same graph, sketch another line to show another object
moving more slowly away from the same starting position.
Label this line 'slower'.
Marcus is making a journey from home to a shop.
For the first part of the journey, he rides his bicycle at a constant speed.
Marcus then stops to talk to a friend.
For the last part of the journey, he rides his bicycle at a lower
constant speed than before.
a
Sketch a distance- time graph for Sam's journey.
b Label each part of Sam's journey on your graph.
81
)
______
3_F_o_r_ce_s_a_n_d_e_n_e_r_9_Y__________)
3
A boat goes straight across a lake. After some time, the boat crosses
the lake again to return to the original position.
The graph shows the journey made by the boat.
Use information in the graph to answer these questions.
a
How far did the boat travel when crossing the lake once?
b
Calculate the speed of the boat crossing the lake the first time.
c
How much time did the boat spend stopped before crossing
the lake again?
d Calculate the speed of the boat crossing the lake the second time.
e
How much time did the boat take for the complete journey?
100
-
90
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--
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20
30
40
50
60
70
80
Time ins
82
)
90
100
11 0
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120
130
140
150
3.3 Describing movement
Activity 3.3.1
My journey
Think about a journey you made recently.
The journey could be walking or any other
method of travel.
The journey could be coming to school or a
longer journey.
Sketch a distance-time graph for that journey.
Label your graph with what each part
represent s.
Swap your graph with someone else.
Can they understand your journey by looking
at the graph?
Can you understand someone else's journey
by looking at their graph?
r
Think like a scientist
Walking and running
In th is activity, you will plan an investigation, make measurements, do ca lcu lations
and draw a d istance-t ime graph.
Work in groups of three or four.
You will need:
• space where you can run safely
• tape measure
• stopwatch
• one sheet of graph paper per person
Method
You need to calculate the average speed of walking for one person in the group, in m/s.
You then need to calculate the average speed of running for one person in the group, in m/s.
It does not have to be the same person.
1
Plan what measurements you wi ll need to make and how you wil l make these
measurements.
2
Make a list of the safety precautions that the person who is running should take.
3
Make your measurements safely and record them in a suitable way.
83
)
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Continued
Questions and results
1
a
Calculate the average walking speed for the person, in m/s.
b Calculate the average running speed for the person, in m/s.
2
Draw a distance- time graph. Put walking and running on the same graph
and label the lines clearly.
3
Explain the difference between the two lines. Refer to distance and time in
your explanation.
Self-assessment
1
2
Decide how confident you are about each of these statements.
Give yourself 5 if you are very confident and 1 if you are not confident at all.
•
I made useful contributions to planning.
•
I made useful contributions to making the measurements.
•
I drew my graph careful ly, neatly and accurately.
Which do you think is better:
•
drawing a distance-time graph for a journey, or
•
describing a journey in words?
Explain your answer.
Summary checklist
D I can sketch a distance-time graph for an object moving at a constant speed away
from a starting position .
D I can sketch a distance-time graph for a stationary object.
D I can sketch a distance-time graph for an object moving at a constant speed back
towards a starting position.
D I can tell whether objects are moving quickly or slowly, or are stationary, from a
distance-time graph.
I can tell what direction an object is moving from a distance-time graph.
I can sketch a distance-time graph from a description of a journey.
I can draw a distance-time graph accurately.
I can read values from a distance-time graph.
.....
3.4 Turning forces
> 3.4 Turning forces
In this topic you wil l:
•
recognise when a force causes something to turn
•
know how to use the term moment
•
be able to calculate the moment caused by a force
Getting started
Key Words
Work in groups.
lever
Make a list of things, such as a door handle, that are turned
by forces.
moment
newton metres
pivot
turn
85
)
______
3_F_o_r_c_
e s_ a_n_d_e_n_e_r_9_Y__________)
Turning effects of forces
When you push down on a door handle, the handle turns.
When you push down on the pedal of a bicycle, the pedal turns.
When you pull on a door, the door turns toward you.
These are all examples of forces that cause an object to tum.
The object that turns is called a lever.
The point around which the lever turns is called the J>ivot.
The lever and pivot are shown in the picture of the bicycle pedals
in Figure 3.4.1.
When you bend your arm, the arm acts as a lever. Your elbow is the pivot.
A bicycle pedal is an example of a lever that turns around
a pivot w hen a force is applied.
The human body has many levers and p ivots.
Can you see more levers and pivots in this picture?
Calculating moments
The moment of a force describes its the turning effect of a force.
The moment of a force depends on:
•
the size of the force (the bigger the force, the bigger the moment)
•
the distance between the position where the force acts and the pivot
(the greater the distance, the greater the moment).
You can calculate a moment from this equation:
moment = force x distance
86
)
3.4 Turning forces
Distance in the equation is the distance from the pivot to the position
where the force acts.
The unit of force is the newton and the unit of distance is the metre.
Therefore, the unit of moment is newton x metre, which is written as
newton metre or Nm.
Remember to use an upper case N and a lower case m when writing Nm.
Worked example
Question
A pulling force of 35 N is needed to open a door. The distance from the door handle to
the door hinges (the pivot) is 0.8 m What is the moment caused by the pull on the door?
Answ er
moment= force x distance
= 35 X 0.8
=28Nm
Worked example
Question
Look a t this diagram. What is the moment caused by
the weight on the arm?
pivot
20N
Answer
moment = force x distance
= 20 X 0.25
= 5Nm
87
)
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Balancing
A seesaw is a type of lever.
People sit on either side of the pivot of a seesaw and
make the lever turn one way and then the other.
The result is that each person moves up and down.
A seesaw will be balanced when the moments on
both sides of the pivot are equal and opposite.
Worked example
Question
Marcus, with a weight of sits at a distance of from the pivot of a seesaw. Arnn, has a
weight of 800 N. Where should Arnn sit to make sure the seesaw is balanced?
Answer
Marcus will exert a moment of 600 x 2 = 1200Nm
For the seesaw to be balanced, the moment on the other side must also be 1200Nm.
moment = force x distance
So distance = moment
'
force
distance = 1200Nm/800N
= 1.5m
88 )
3.4 Turning forces
Questions
1
a
Describe what is meant by the word 'moment' in physics.
b Write the equation that links moment,
force and distance.
c
2
Write the unit of moment.
Jon has a spanner for turning a nut. The direction that
the nut must turn is shown by the arrow. The pivot is
in the centre of the nut.
a
Which arrow shows the direction that Jon should
push on the spanner to produce the largest
moment in the direction needed to turn the nut?
B
wrench
nut
nut will turn
this way
D
C
Write the letter.
b
3
Explain your answer to a.
The drawing shows a door handle.
4N
Sofia pushes on the door handle with a force of 4 N at
the position shown in the drawing.
i
Calculate the moment caused by this force.
4
The drawing shows a bicycle brake lever.
A moment of 1.8 N is needed to tum this brake lever.
Calculate the force needed at position F to produce a
moment of 1.8 Nm.
5
0.12 m
Zara weighs 450N. Zara sits on a seesaw at a
distance of I. 5 m from the pivot.
Sofia weighs 500 N .
'
F
l
Sofia sits on the seesaw on other side of the pivot
from Zara.
Calculate the distance from the pivot that Sofia must
sit to balance the seesaw.
89
)
______
3_F_o_r_ce_s_a_n_d_e_n_e_r_9_Y__________)
Activity 3.4.1
Identifying moments
Use old magazines to find pictures.
Cut out pictures showing things that use moments to work.
Remember: anything that turns when pushed or pulled uses moments.
Stick the pictures to a large piece of paper to make a display.
Write the name of the object beside it.
Think of a title for your display.
Think like a scientist
Calculating moments
In this investigation, you wi ll investigate how the force needed to turn an object
varies with distance from the pivot.
Work in groups of two or three.
You will need:
• metre ru le
• ruler
• newton meter
• string
• sticky tape
• 2 clamp stands
• elastic (rubber) band
-
• G-clamp
Set up the apparatus as shown in the diagram.
clamp stand
loop of string stuck to
meter rule with tape
tpivot
G-clampto
secure clamp
stand to table
top
90 )
elastic band
metre rule
loop of string stuck to
meter rule with tape
newton meter
clamp stand
3.4 Turning forces
Continued
Make a prediction about what wi ll happen to the force needed to pull the metre rule
down as the distance between the force and the pivot decreases.
Method
1
Move the loop of string with the newton meter as far from the pivot as you can.
2
Record the distance between the pivot and the string.
3
Raise the newton meter so it is not pulling down on the metre ru le.
4
Use the newton meter to pul l down on the metre ru le. The distance that you pull
depends on the strength of the elastic band. The metre rule needs to be pu ll ed
down far enough to get a reading of about 1 N at the furthest point from the pivot.
5
Record this distance. This will be the distance you pull down on the metre rule
each time.
6
Record the force.
7
Repeat this, pulling the metre rule down the same d istance each time.
Each time, use the loop of string to move the newton metre closer to the pivot.
8
Your results should be a set of distances and forces.
9
Decide whether you need to repeat any of your measurements.
Results and questions
1
Describe how you made the experiment safe.
2
Record your results in a table. Make sure that you record distances in metres,
so you may need to convert from cm or mm. Remember to reverse the order
of your resu lts, so in the table the distances are increasing.
3
Draw a line graph of your results. Put distance on the horizonta l axis and
force on the vertical axis.
4
Explain the pattern in your resu lts.
5
Was your prediction correct?
6
Explain any improvements you cou ld make to the method that would help
get more accurate results.
Self-assessment
1
Describe anything you did during the investigation to help get more accurate results.
2
a Did you repeat any of your measurements?
b Explain your answer to part a .
91
)
______
3_F_o_r_ce_s_a_n_d_e_n_e_r_9_Y__________)
Summary checklist
D I can understand that forces can cause turning effects.
D I can understand what is meant by the term moment.
D I know and can use the equation that links moment, force and distance.
D I know the unit of moment.
3.5 Pressure between solids
> 3.5 Pressure between solids
In this topic you will:
•
recognise that forces can cause pressure on an area
•
understand what affects pressure
•
be able to calculate the pressure caused by a force on an area
--------
Getting started
Key word
Work in groups.
newtons per
square metre
The nai l in the picture has a sharp point at one end.
point
Make a list of some other objects that have sharp points or
sharp edges.
pressure
What are these things used for?
surface area
sharp
______
3_F_o_r_c_
e s_ a_n_d_e_n_e_r_9_Y__________)
The pushing effect of a force
The picture shows a knife being used to cut modelling clay.
What could you do if the clay was difficult to cut?
The knife works because the force used to push down on the clay causes
pressure on the clay.
You can think of pressure as the pushing effect of a force.
Suppose the clay is difficult to cut. How could you increase the pushing
effect of the force?
You could:
•
increase the force on the knife; as the force increases, the pressure
increases
•
use a sharper knife (a sharp knife has less surface area in contact
with the clay); as the area decreases, the pressure increases.
The equation linking pressure, force and area is
Pressure= force
area
Pressure is force divided by area. The unit of force is the newton and
the unit of area is the metre squared. That means the unit of pressure is
newtons per metre squared, or N/m2•
Sometimes you can use smaller areas, measured in cm2 • If the area is
in cm2 then the unit of pressure will be N/cm2• If the area was in mm 2,
what would the unit of pressure be?
Some things have large areas to decrease pressure; others have small
areas to increase pressure.
94
)
3.5 Pressure between solids
The camel has large feet. This
means the force from the weight
of the camel is applied over a
large area. The pressure on the
sand is decreased, so the camel
will not sink in the sand.
The woman in the picture is
lying on a bed of nails. Each nail
has a sharp point on the end.
The weight of the woman acts
on many hundreds of nails, so
the pressure from each nail is
very small.
The end of this pin has a sharp
point. The sharp point has a
small area to increase pressure.
The increased pressure means
the pin will easily go into wood
or card.
Scissors have sharp blades. The
area along the cutting edge
of each blade is small. This
increases the pressure, making
things easier to cut.
95
)
______
3_F_o_r_
c e_s_a_n_d_
e _ne_r_9_Y_ _ _ _ _ _ _ __,)
Calculating pressure
Worked example
Question
Question
Imagine an elephant standing on four feet,
as shown in the picture.
T he total weight of a bicycle and rider
is 1000N.
The bicycle has two tyres in contact with the
ground and the weight is supported equally
on both tyres.
The area of each tyre in contact with the
ground is 5 cm2
What is the pressure that each tyre exerts
on the ground?
The weight of the elephant is 50000N.
T he total area of a ll fou r feet is 0.4m2•
What is the total pressure that the elephant
exerts on the ground?
Answer
Answer
Pressure ::: force
area
weight on each tyre ::: 1OOO
2
::: SOON
_ 50000
0.4
Pressure::: force
area
::: 1 25 000 N/m2
_ 500
2
T he unit of pressure here is N/m because
the area is given in m 2 •
- - 5-
::: 100 N/crn 2
Notice how the unit of pressure here is N/cm 2
because the area of the tyres is given in cm 2 •
96
)
3.5 Pressure between solids
Continued
Question
A hammer is used to push a nail into wood.
The area of the point at the end of the nail is 1.5 mm 2 •
T he pressure needed for the nail to go into the wood is 50 N/mm2
Calculate the force needed from the hammer.
Answer
rce
Pressure = fo
area
so, force = pressure x area
= 50 X 1.5
= 75N
Questions
1
a
Write down the equation that links pressure, force and area.
b Use the equation to explain why
a nail that goes into wood has a sharp point
ii
2
Write down the unit of pressure when force is in newtons and area is in:
a
3
shoes for walking on snow are wide and flat.
m2
b cm2
c
mm 2
A box has a weight of 60N. The area of the box in contact with the
ground is 0.5 m 2•
Calculate the pressure that the box exerts on the ground.
Show your working and give your answer in N/m2 •
4
A car has a weight of 8000 N. The car is supported by 4 tyres.
The weight on each tyre is equal.
The area of one tyre in contact with the ground is 150cm2 •
Calculate the pressure that one tyre exerts on the ground.
Show your working and give your answer in N/cm2.
5
A thumb tack has an area of 0.5 mm2 in contact with a wall.
A pressure of 40 N/mm2 is needed for the drawing pin to go into
the wall.
Calculate the force needed to push the drawing pin into the wall.
Show your working and give the unit with your answer.
97
)
______
3_F_o_r_ce_s_a_n_d_e_ne_r_9_Y_ _ _ _ _ _ _ __,)
Think like a scientist
Calculating pressure
In this investigation, you wi ll investigate how the pressure that a person exerts on
the floor varies.
Work in groups of two or three.
You will need:
• a person who is willing to be weighed, or who knows their body mass
• a bathroom scale, if body mass is not known
• sheets of squared paper
• pencil
Method
1
Measure or record the body mass of the person.
2
Convert the mass to weight using:
weight in N = mass in kg x strength of gravity in N/kg
Take the strength of gravity as
3
Ask the person to place one foot on a piece of squared paper.
They can do this while wearing shoes.
4
Use the pencil to draw around the foot of the person.
Questions
1
Use the shape of the outline on the squared paper to work out the area of
the foot in cm 2 .
2
Calculate the area of both feet.
3
Calculate the pressure that the person exerts on the ground when they are:
a
standing equa lly on both feet
b standing on one foot.
4
Explain the difference in your answers to 3a and 3b.
5
Now ask the same person to put the front of one foot on squared paper as
if they were standing on their toes.
6
Use the same method as above to work out the area of the front of the foot in cm 2 .
7
Calculate the pressure exerted by the person on the ground when standing on the
front of one foot.
8
A person can be supported by the front of one foot during some everyday activities.
Give an example of such an activity.
98 )
3.5 Pressure between solids
Continued
9
a Describe how you cou ld work out the area in contact with the ground when
the person is lying down.
b
Predict how the pressure would change when the person was lying down
compared to standing.
ii
Explain your answer.
Self-assessment
1
2
Decide how confident you are about each:
a
how force affects pressure
b
how area affects pressure.
Decide how confident you are about:
a
ca lculating pressure when you know the force and the area
b
working out the unit of pressure using the units of force and area.
Summary checklist
D I can understand that pressure is the pushing effect of a force.
D I know and can use the equation that links pressure, force and area.
D I can understand how the unit of pressure can be worked out from the
units of force and area.
•-
_ _ _ _ _3__
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e _r9_Y_ _ _ _ _ _ ____,)
> 3.6 Pressure in liquids
and gases
•
recall how particles move in liquids and gases
•
understand how particle movement causes pressure in liquids
and gases
•
predict how changes in liquids and gases affects the pressure
Getting started
Key words
Work individually.
altitude
Draw a diagram to show how particles are arranged in:
atmospheric
pressure
a
a liquid
b
a gas.
collide
container
depth
sea level
100)
~
3.6 Pressure in liquids and gases
Pressure in liquids
Look at the picture of a dam. The wall of this dam is wider at the
bottom than it is at the top.
The water comes out with more force t han from t he upper gaps
Behind the wall of the dam, the water is almost to the top of the wall.
You can see water coming out from two levels.
The water coming out close to the top is coming out with less force.
The water coming out from further down is coming out with more force.
This is because pressure in the water increases with depth.
The wall is wider at the bottom to make the wall stronger where the
pressure from the water is greatest.
Pressure and depth in liquids
The pressure in a liquid increases with depth, but why?
As you go deeper in a liquid, there is more liquid above your position.
The weight of this liquid, caused by gravity, pushes on the particles of
the liquid.
When the particles of the liquid are pushed, they move with more force.
As the particles in a liquid are moving randomly in all directions, then
the pressure in the liquid is equal in all directions.
101)
______
3_F_o_r_c_
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Pressure in gases
Before you blow up a balloon, there is a small volume
of air inside the balloon. The balloon is open at one
end, so the pressure of the air inside is the same as the
pressure of the air outside.
As you blow air into the balloon, you are adding
more gas particles.
Particles in a gas move randomly and collide with the
walls of the container. The container is the balloon.
Every time a gas particle collides with the wall of
the container, the particle exerts a small force on
the wall.
The more particles there are in the gas, the more collisions happen
with the walls, and so the force on the walls increases.
As this force is exerted on an area, the force causes pressure.
The pressure inside the balloon gets bigger as you blow in more air,
pushing the walls of the balloon outwards.
Look at the tyre in this picture.
The pressure of t he air in this tyre is too low.
102)
Particles in a gas move
random ly and collide wit h
the walls of t he container
causing pressure.
3.6 Pressure in liquids and gases
The air inside the tyre is at low pressure. The pressure is not enough
to support the weight of the vehicle.
If more air is put inside the tyre, the pressure will increase. More
collisions will happen with the inside waUs of the tyre, pushing the
tyre outward and supporting the vehicle.
Pressure and depth in gases
As with liquids, the pressure in a gas increases with depth.
Most people on Earth live at low altitude. Altitude is height above sea level.
The Earth's atmosphere, which we call air, is made from gases.
The atmosphere extends to a height of about above sea level.
Sea level is, therefore, where the atmosphere is at its deepest.
So, at sea level, atmospheric pressure is highest.
As you go higher in the atmosphere, two variables that affect
atmospheric pressure change:
•
the number of particles in of air decreases, so the concentration
of gas particles decreases
•
the weight of air above your current position decreases.
Atmospheric pressure at sea level is about. This pressure is the
equivalent of the weight of two large elephants pushing on every of
surface! We are not aware of the pressure from the atmosphere because
we live in the atmosphere all the time.
Effects of atmospheric pressure
The effect of atmospheric pressure can be shown by pumping
the air out of a metal container.
Before the air is pumped out, the pressure on the inside of the
container is equal to the pressure on the outside.
When t he air is pumped out, the p ressure inside the container
becomes close to zero. The pressure on the outside does
not change.
The container is crushed by the pressure of the air outside
the container. The picture shows a containercrushed by
atmospheric pressure.
103 )
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Pressure and temperature in gases
As the temperature of a gas increases, the speed of the particles in the
gas mcreases.
When particles are travelling faster, their collisions exert more force.
This means that increasing the temperature of a gas will
increase the pressure of the gas.
High pressure can be used to cook food.
The picture shows a type of cooking pot called a
pressure cooker.
Water and food are placed inside the pressure cooker.
The pressure cooker has a sealed lid. When the water
boils, the steam cannot escape so the pressure of the
gas inside increases.
On top of the pressure cooker, there is a weight to
control the pressure and valves that allow steam to
Steam inside a p ressure cooker is at higher
pressure because of the high temperature.
escape, once the equired pressure has been reached.
Questions
1
a
Explain why submarines that go to the deepest parts of the
oceans must be very strong.
b Explain why the wall of a dam is thicker at the bottom than
at the top.
2
The sketch graph shows how the pressure in a liquid changes
with depth in the liquid.
a
Explain the pattern shown in the graph.
b Copy and complete the sentence using the best word.
Pressure
Use information in the graph.
When the depth in the liquid doubles, the pressure in the
liquid ................... .
3
A fish is in water. The water exerts pressure on the fish.
Which of these causes pressure on the fish? Write one letter.
A
the weight of water beside the fish
B the weight of water all around the fish
C
the weight of water above the fish
D the weight of water below the fish
4
Marcus plays basketball. The ball is filled with air.
a
104 )
Explain what causes the pressure inside the ball.
Depth in liquid
3.6 Pressure in liquids and gases
b The ball is too soft and does not bounce properly. Marcus uses a
pump to put more air in the ball.
Explain how putting more air in the ball will change the pressure
inside the ball.
c
Marcus notices that the pressure inside the ball is lower on a
cold day and higher on a hot day.
Explain why the pressure inside the ball is higher on a hot day.
A metal container is connected to a vacuum pump. A vacuum pump
removes all the air from inside the container.
5
T here is now a vacuum inside the container.
a
Explain why the pressure in a vacuum is zero.
b The container collapses when there is a vacuum inside. Explain why.
~
Think like a scientist
Observing the effects of pressure
Part 1: Pressure and depth in liquids
In this investigation, you wi ll observe the effect of pressure increasing with depth, in water.
Work in groups of two or three.
You will need:
• a 1 or 2 litre empty plastic bottle
• adhesive tape
• something to make small holes in the side of the bottle
• large tray or sink to col lect water
Method
1
Make three small holes in the side of the bottle at different
heights. Try to make the holes the same size.
2
Predict what will happen when the bottle is filled with water.
3
Now use one piece of adhesive tape to cover all the holes.
4
Place the bottle in the tray or the sink.
5
Fill the bottle with water, but do not put the lid on the bottle.
6
Pull off the adhesive tape to open the holes.
7
Watch what happens.
continued
105 )
______
3_F_o_r_ce_s_a_n_d_e_ne_r_9_Y_ _ _ _ _ _ _ __,)
Continued
Questions
1
Did your observation fit with your prediction?
2
Draw a labelled diagram to show what you observe.
3
Explain what you observed, using ideas about pressure.
Part 2: Pressure and temperature in gases
In this activity, you will observe the effect of changing temperature on the
pressure in a gas.
Work in groups of two or three.
You will need:
• an empty plastic bottle (0.5- 2 litre) with lid
• access to a warm place
• access to a cold place, such as a refrigerator
Method
1
Take the lid off the bottle.
2
Leave the bottle and the lid in a warm place for 5-10 minutes.
3
Put the lid tightly on the bottle without squeezing the bottle.
Do this while the bottle is still in the warm place.
4
Put the bottle into a cold place for 15-20 minutes.
5
Observe what has happened to the bottle.
Questions
4
Draw a diagram of the bottle before and after the activity.
5
What happened to the pressure of the air inside the bottle when it was
moved to the cold place?
6
Explain your answer to 5.
7
Predict what wou ld happen if you did this activity the other way around.
The open bottle starts in the cold place, then the closed bottle is taken
to a warm place.
Include ideas about particles and pressure and include the observation
that you would make.
106)
0
3.6 Pressure in liquids and gases
Continued
Peer-assessment
Swap your answers for these activities with another group.
Rate their score for each answer on a scale of 0-3.
3 means very good and we ll explained.
2 means good with some explaining.
1 means difficult to understand, but some explaining is given.
0 means you cannot understand the answers or they are incorrect.
[_::$~gr:ii.tD~ -; ~E~~k·!r~1·
D I can understand what causes pressure in a liquid.
D I can understand how pressure changes with depth in a liquid.
D I can understand what causes pressure in a gas.
0
I can understand how altitude affects atmospheric pressure.
D I can understand how the quantity of gas in a container affects the pressure.
D I can understand how the temperature of a gas in a closed container affects the pressure.
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> 3.7 Particles on the move
In this topic you will:
•
describe how random movement of particles causes diffusion
•
understand how diffusion happens in liquids and gases
Getting started
Work in groups to discuss the answers to these questions.
1
How can you smell food cooking when you are some
distance away from the food?
2
When you pour orange juice into water, why does all the
water eventually turn o range?
concentration
diffusion
3.7 Particles on the move
Mixing gases
The particles in a gas move randomly. Both the speed of the particles
and the direction of the particles are random.
If we mix two gases in one container, each one will have particles that
move randomly.
That means each gas will spread to fill the container.
The movement of the particles of each gas is called diffusion.
Diffusion means the overall random movement of particles from an
area where they are in higher concentration to an area where they are
in lower concentration. Concentration is the number of particles in a
particular volume.
Look at the diagrams. They show how two gases diffuse.
1
At the start, the tap is closed.
The white gas particles are at high concentration
on the left, and zero concentration on the right.
The red gas particles are at high concentration on
the right, and zero concentration on the left.
2
The tap is opened and the gases start to spread out
(diffuse). At random, some particles of each gas will
pass through the space where the tap opens.
The white gas particles are now at quite high
concentration on the left, and low concentration
on the right.
The red gas particles are at quite high concentration
on the right, and low concentration on the left.
3
After some time, the gases have completely diffused.
There is equal concentration of both gases on
both sides.
Diffusion stops when the concentrations are equal.
However, the movement of individual particles does
not stop when diffusion stops.
Diffusion explains how you can smell food cooking.
When food is heated, some particles in the food change state and
become gas.
109 )
_ _ _ _ _ _3__
Fo
_ rc_e_s_a_n_d_e_n_e_r_9_
Y_ _ _ _ _ _ _ ___,)
The gas particles from the food move randomly
and so spread out through the air by diffusion.
The strength of the smell will get stronger as you
move closer to the food. This is because the
concentration of the particles is higher, the closer
you get to the source of the particles.
Many animals use this change in strength of
smell to find food.
Mixing liquids
Diffusion also happens in liquids. Particles in a liquid also move at random.
The picture shows what happens when blue ink is added to water.
The blue ink moves from the area of high concentration to the areas of
low concentration, until it is completely diffused throughout the water.
~, . , . I
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l
.
~
.
Speed of diffusion
The speed of diffusion depends on:
•
the difference in concentration of the particles
•
temperature.
The bigger the difference in the concentrations of the particles, the faster
the diffusion.
The higher the temperature, the faster the diffusion. Higher temperature
makes particles move faster, so the particles can spread out faster.
For example, when you make a cup of tea, the tea diffuses through the
water. It diffuses faster in hot water than it does in cold water.
110 )
~
1
~
•
#
3.7 Particles on the move
Questions
1
Zara's mother opens a bottle of perfume. Zara is at the other side
of the room.
After a few minutes, Zara can smell the perfume.
a
Which of these explains why Zara smells the perfume?
Write one letter.
A
AIJ the gas particles of the perfume move in one direction.
B
All the gas particles of the perfume move randomly.
C
All the particles in the air move in one direction.
D All the particles in the air are stationary (not moving).
b Which of these changes would result in Zara smelling the
perfume in a shorter time?
In each case, no other variable changes.
There is more than one correct answer.
A
The air in the room is at a higher temperature.
B Zara moves further away from the bottle of perfume.
C
Zara's mother puts the lid on the perfume bottle.
D The perfume in the bottle is at a lower temperature.
2
Describe what is meant by the term 'diffusion' .
3
The diagram shows two types of particle in containers,
A and B. The containers have the same volume.
a
Explain whether the particles in the containers are
in solid, liquid or gas state.
b Explain how the concentrations of the blue
particles compare in containers A and B.
c
4
container A
~ ~
~
~
~
~
'-
~"
'1
~
Explain how the concentrations of the red particles
compare in containers A and B.
Sofia is making an orange flavour drink. She pours a
small volume of concentrated orange juice into a glass.
She then adds water to the glass until the glass is full.
a
-~
~-
container B
~ ~
~
~
(j
~
~e
ll
~
"
'- f) G
'1
- -_-~
_ __..
Explain how the orange colour from the juice
spreads into the water.
b Arnn says: 'When the orange colour has stopped
spreading, the particles in the liquid have stopped
moving.'
Explain whether Arun is correct.
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111 )
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Which of these will result in diffusion?
5
Write the letters for all the correct statements.
A
adding milk to coffee
B adding sand to water
C
adding salty water to pure water
D allowing gas from a cylinder to escape into the air
E
throwing small pieces of rock into the air
Activity 3.7 .1
Watching diffusion
In this activity, you will observe the diffusion of a coloured solution in water.
You will need :
• a transparent container, such as a 200cm 3 (or larger) glass beaker
• ink, such as food dye
• dropper pipette
• water
• a glass tube or drinking straw
Method
1
Fill the container with warm water.
2
Leave the container to stand for a few minutes so the water stops moving.
3
Use the dropper pipette to add one or two drops of dye to the bottom of
the water in the beaker.
4
Observe what happens.
Q uestions
1
Write about what you did in this activity. Write this in your own words and
do not copy the method shown here.
2
Make a series of labelled drawings to show your observations in this activity.
3
Predict what wou ld happen if the activity was repeated with water at
higher temperature.
112 )
3.7 Particles on the move
Think like a scientist
The effect of temperature on the speed of diffusion
In this investigation, you will investigate how temperature affects the rate of
diffusion in liquids.
Work in groups of two or three.
You will need:
• three or more identical beakers
• water
• a way to heat the water
• a way to cool the water (optional)
• wat er-so luble ink
• thermometer
• stopwatch
• dropper pipette
• measuring cylinder
Method
1
Add equal volumes of water at different temperatures to each of your beakers.
2
Measure and record the temperature of the water in each beaker.
3
Use the dropper pipette to carefully add a small vo lume of the ink to the
bottom of each beaker. Squeeze the top of the pipette gently so the ink
does not squirt out into the water and start mixing.
Add the ink to the water in order from the lowest to the highest temperature.
4
Use a stopwatch to time diffusion process in each beaker.
5
Stop the stopwatch when the ink has fully spread out through the water of
the beaker being tested.
Questions
1
Describe the trend in your results.
2
Explain this trend.
3
Explain why you used equal volumes of water in all the beakers.
4
Suggest at least two improvements to the method that would give better resu lts.
Peer-assessment
Swap your answers with another group.
You wi ll assess their answers to 2 and 4.
Instead of marking their answers, write some feedback to the group.
Include:
•
what they have done well in their answers
•
how they could improve their answers.
113 )
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Summary checklist
D I know how to describe diffusion.
D I can understand how diffusion happens in gases.
D I can understand how diffusion happens in liquids.
D I can understand that the speed of diffusion is affected by the difference
in concentration and by the temperature.
0
0
..c
..c
C
C
E
0
114 )
Check your progress
3.1 An object has balanced forces acting.
Which of these describes the movement of the object?
[11
Give two letters.
A
The object could be moving at a constant speed in a straight line.
B
The object could be moving at a constant speed in a circle.
C
The object could be stationary.
D
The object could be getting faster in a straight line.
3.2 Describe the effects of the unbalanced forces on each of these objects.
a
b
C
A bicycle is moving in a straight line. There is an unbalanced force
opposite to the direction the bicycle is moving.
[1 ]
A car is moving in a straight line. There is an unbalanced force in
the same direction as the car is moving.
[11
A ball is moving in a straight line. There is an unbalanced force
sideways to the direction the ball is moving.
[1 ]
3.3 Which of these is the standard unit of speed used by scientists?
Write one letter.
A
km/h
B
mis
C
N/cm2
D
Nm
3.4 Marcus goes running. After some time, Marcus gets tired and starts walking.
Marcus does not stop.
Sketch a distance- time graph for Marcus.
3.5 A train travels a distance of in at a constant speed.
a
Draw a distance- time graph for the train.
b
Calculate the speed of the train. Show your working and give the unit
with your answer.
[1 1
______3__
Fo
_ rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ _ _)
3.6 There have been different units of measurement through history.
This picture shows the unit of length called the rod.
One rod is the total length of the left feet of 16 people.
In the picture, the 16 people have been chosen at random.
a
Explain one disadvantage with the rod as a unit of length.
[11
b
Explain one advantage of the rod as a unit of length.
[1]
3.7 Zara has a metre rule, a stopwatch and a newton meter.
Zara can directly measure some quantities with this equipment.
Zara must calculate some quantities that cannot be directly measured
using this equipment.
Copy this table.
Can be measured
Must be calculated
[2]
Write each of these quantities into the correct column in the table.
force
moment
length
area
pressure
time
speed
3.8 a
b
Write the equation that links moment, force and distance.
[1]
Arnn is trying to turn a nut with a spanner.
Arnn exerts his maximum force on the spanner, but the nut will not turn.
3.9 a
b
Explain why Arnn can make the nut turn if he uses a longer spanner.
[2]
Write the equation that links pressure, force and area.
[1]
T he picture shows fou r different types of shoes.
Give the letter of:
ii
the shoes that will be best for not sinking in snow
[1 ]
the shoes that could make holes in a soft wood floor.
[1 ]
3.10 Which statement is true about a liquid?
Write one letter.
A
Pressure increases with depth.
B
Pressure decreases with depth.
C
Pressure does not depend on depth.
D
There is no pressure in a liquid.
3.11 Write down two variables that wiJI increase the speed of diffusion in a gas.
[1 ]
_ _ _ _ _ _3__
Fo_rc_e_s_a_n_d_e_n_e_r_9_Y_ _ _ _ _ _ _ ___,)
Project: Making a balance for weighing
This project is about using moments to find the weights of objects. You wil l make
a balance and then use it to find some unknown weights.
Background
The earliest balances for weighing
needed equal weights on both
sides of the balance.
The unknown weight was placed
on one side, and known weights
were added on the other side until
the system balanced.
A system such as this is balanced
because there are two moment s
acting.
One moment tries to pull one
side down.
The other moment tries to pull
the other side down.
When the moments are equal
and opposite, the system is balanced.
This happens when the weights are equal because the distances from the pivot
are also equal.
Your task
Make a balance that can be used to weigh a range of different weights without
changing the known weight.
Your balance wi ll work in a different way to the one in the picture, so yours will
not look like this.
Work in groups.
You can use equipment such as:
•
a metre rule
•
a triangular prism
•
a known weight
•
any other equipment that your teacher makes available.
118 )
Project
Continued
Remember:
•
do not confuse weight with mass
•
weight is a force
•
the moment caused by a force depends on the distance from the pivot.
When your balance is made and working, you can demonstrate to the class
how it works.
Ecosystems
> 4.1 The Sonoran Desert
In this topic you will:
•
find out about some of the animals and plants that live
in a desert
•
think about how these animals and p lants interact with
each other
•
learn what an ecosystem is
•
think about some of the different habitats in a
desert ecosystem
Cacti (the plural of cactus) are plants that are adapted to live in
deserts.
adaptations
Look at a cactus, or a picture of one.
ecosystem
With a partner, discuss these questions.
•
Why is a desert a difficu lt place to live?
•
How are cacti adapted to live in a desert?
ecology
environment
food web
habitat
interact
nectar
nocturnal
pollen
pollinating
4.1 The Sonoran Desert
A desert in Arizona
The photograph shows the Sonoran Desert in Arizona,
in the USA.
Deserts are not easy places for animals and plants to live.
Deserts do not get much rainfall, so the organisms that live
there must have adaptation~ that help them to survive with
little water.
The tall plants in the photograph are saguaro cacti. They grow
very slowly, and those in the photograph may be more than
I 00 years old. Their roots spread out widely just underneath
the soil, ready to absorb any rain that falls.
Many animals live among the cacti and other desert plants.
Gila woodpeckers make holes in the cacti, to make their
nests. Other birds also visit these holes.
Cactus wrens often use a different kind of cactus, called
a teddy bear cholla, to make their nests. Teddy bear
chollas are so spiky that very few other animals will get
close to them. So the cactus wren's eggs and young ones
are protected from predators.
______4__E_c_o_s_y_st_e_m_s_____________)
During the hot days, lizards, tortoises and other animals
rest in the shade of the plants, or burrow into the soil
where it is cooler. At night, when the temperature falls,
kangaroo rats come out to feed, wary of their predators
such as rattlesnakes and coyotes.
In the Sonoran Desert, it usually rains heavily at least once a
year. When the rains come, the desert is transformed. Many
plants quickly produce flowers.
Insects feed on the nectar and pollen in the flowers, helping
the plants to reproduce by pollinating them. At night, bats
feed on nectar from the flowers of agave plants.
A kangaroo rat
Seeds fall to the ground and are colJected by ants, to take
into their nests to provide a food store. Many months or
years later, some of the uneaten seeds may germinate to
produce new plants.
Interactions in the Sonoran Desert
As you read the information above, and looked at the
photographs, you may have realised that all the different
animals and plants depend on each other. They interact
with each other. The actions of one organism affect
another.
A bat feeding on agave nectar
4 .1 The Sonoran Desert
Activity 4. 1.1
Interactions between organisms in the desert
Work with a partner.
You will need:
• a large sheet of paper
• coloured pens
• (optional) pictures of the animals and plants in the desert, that you can cut out
• (optional) scissors and glue
Read the information about life in the Arizonan Sonora Desert, and look at the
photographs. Make a list of different ways that the animals and plants interact
with one another.
Now think about how you cou ld show these interactions in a picture. On a piece
of rough paper, make a rough sketch of the design for your picture.
Build up your picture on a large sheet of paper. You could draw pictures of the
organisms, or stick cut-out pictures of them onto the paper. Write descriptions
about how they interact with each other.
Non-living things in the desert
It is not only other organisms that affect the plants and animals
in the Arizona desert. There are also interactions between the
organisms and the non-living parts of their en\'ironment.
• Light: The bright sunlight helps the plants to photosynthesise,
producing food that other organisms can eat.
•
Temperature: The temperature is often very high during the
day, but much lower at night. Some animals are nocturnal,
which helps them to avoid overheating or drying out. It is
cooler underneath the soil, so some animals - such as the
tarantula in the picture - dig burrows for shelter during
the day.
•
Soil: Rocks and soil provide minerals for the plants to grow,
as well as building material for ground-nesting birds.
123 )
______4__E_c_o_s_y_st_e_m
_s_ _ _ _ _ _ _ _ _ _ _ _)
•
Water: All organisms need water to keep their cells
alive. Rain, when it comes, allows them to become
more active and to reproduce.
•
Air: The desert air provides carbon dioxide for the
plants to use in photosynthesis, and oxygen for all
the organisms to use in respiration.
The organisms also affect their environment. For example,
droppings from the kangaroo rats become part of the soil.
The gases that they take in and give out affect the composition
of the air.
The desert ecosystem
Everything in the desert interacts with
everything else. All of these interactions
make up the desert ecosystem. An
ecosystem is a network of interactions
between all the living organisms and the
non-living things around them.
Some of the interactions in an ecosystem
involve food webs. Remember that plants
are the producers in a food web. They
use energy in sunlight to make food. As
animals eat the desert plants and each
other, the energy is passed through the
desert food web.
Food webs are a very important part of
the interactions in an ecosystem, but they
are not the only interactions. For example,
plants may provide places for some of the
animals to make nests. Plant roots help to
hold the soil together, so that it does not
wash away when it rains. Animals help
plants to reproduce by pollinating their
flowers or spreading their seeds.
/
,ed-1.,;led hawk~
~ ------~
collared lizard
/
kangaroo
rat
\
li1I
prickly pear cactus
A food web in t he So noran Desert.
The interactions in an ecosystem are usually very complicated. The
study of ecosystems is called ecology. No ecologist would ever claim
to have discovered all of the different interactions in an ecosystem.
There is always something new to find out, even in an ecosystem that
scientists have been studying for a long time.
124)
~
rattlesnake
grasshopper
/
•
brittlebrush
4. 1 The Sonoran Desert
Questions
1
Name two producers in the diagram of a food web in the
Sonoran Desert.
2
Explain why the food web could not exist without the producers.
3
What do the arrows in the food web represent?
4
Give two examples of interactions between organisms in the desert
that are not to do with feeding.
Habitats in a desert ecosystem
The place where an organism naturally Jives is called its habitat.
There are many different places to live in a desert.
•
The habitat of a saguaro cactus is the open desert.
•
The habitat of a Gila woodpecker is a saguaro cactus (where it
makes its nest) and the air and ground in the open desert (where
it collects food).
•
The habitat of a desert ant is underneath the rocks and soil and
on the soil surface.
•
Termites live at the base of the saguaro stems.
•
Sap beetles live inside the saguaro flowers.
•
Kangaroo rats live in burrows and come out to look for food
at night.
Question
5
Explain the difference between an ecosystem and habitat.
Activity 4. 1.2
·-
How a species fits into the desert ecosystem
Work in a group of three or four for this activity.
You are going to choose one species that lives in the desert. You could
continue to think about the Sonoran Desert in Arizona, or you could choose
a different desert.
Investigate how your species interacts with other organisms, and with the
non-living things around it. You could choose one of the species mentioned
in this topic, or a completely different species.
125 )
______4__E_c_o_s_y_st_e_m_s_____________)
Continue d
Use the internet and the library to find out as much as you can about your
species. Concentrate especially on how your species interacts with other
organisms, and with its environment. For example, you could try to find out:
•
what it eats, and what eats it
•
the habitat it lives in within the desert ecosystem
•
how the species is adapted to survive in its habitat
•
how its actions (other than feeding) affect other organisms,
or non-living parts of the ecosystem
•
how other organisms and non-living things affect it (other than feeding).
Use your information to make an illustrated poster or presentation that you can
share with the rest of your class.
Questions
6
Where did you find the best and most interesting information?
7
When you used the internet to find information about your species:
a
which web sites were most relevant for your research?
b how did you choose web sites that were most likely to provide
correct information?
I can describe some of the interactions between the organisms in
a desert ecosystem.
D I can describe some of the interactions between the organisms
and the non-living parts of the environment in a desert ecosystem.
D I can name some of the different habitats in a desert ecosystem.
D I can explain the difference between a habitat and an ecosystem .
126)
4.2 Different ecosystems
> 4.2 Different ecosystems
In this topic you will:
•
learn about some of the many different kinds of ecosystem
on Earth
•
describe some of the different habitats in an ecosystem
Getting started
Work with a partner.
Marcus says that an ecosystem is a place.
Sofia says that an ecosystem is not just a place - it is more than that.
Who is correct? Think about this on your own, then share your
ideas with your partner.
______4__
E_
co_s_y_s_te_m_
s _ _ _ _ _ _ _ _ _ ____,)
More about ecosystems
The ecosystem in the Arizona Desert is just one of many different
ecosystems on Earth. Here are th ree more examples of ecosystems:
mangrove forests, sea ice in the Arctic Ocean, and a rice paddy.
Mangrove forest
•
Mangroves are trees that can grow with their roots
in sea water. They form forests along the coasts of
many tropical countries
•
Young fish live among the mangrove roots, safe
from larger fish that might eat them. Mud skippers
climb out onto the mud when the tide is out,
feeding on whatever they can find.
•
As the mangrove leaves fa ll onto the mud,
they are decomposed by bacteria. Prawns
and crabs eat the partly decomposed leaves.
•
Crab-eating macaques, a type of monkey,
climb through the trees and catch crabs on the
tree roots and mud.
Sea ice in the Arctic Ocean
•
During the winter in the Arctic Ocean, it is so cold
that some of the sea water freezes.
•
Seals hunt for fish in the water, but have to come to
the surface to breathe air.
•
Polar bears patrol the ice, looking for seals to kill
and eat. Polar bears are good swimmers, and can
move from one ice floe to another.
•
Arctic foxes also look for food on the ice.
•
Enough light passes through the ice to allow tiny
algae (single-celled plants) to grow on the underside
of the ice floes.
•
Tiny shrimp-like organisms eat the algae.
Fish eat the shrimps.
128 )
·-·
4.2 Different ecosystems
Rice paddy
•
Not all ecosystems are natural. This area of rice
paddies in Malaysia is farmed by people.
•
At some times of year, the paddy fields are flooded
with water. Algae grow in this shallow water, and
on the mud at the sides of the flooded areas.
•
Fish swim into the flooded paddies from the
irrigation canals. Frogs and dragonflies breed
in the water.
•
Because the water is shallow, it heats up quickly
during the day, and cools down quickly at night.
•
Farmers often add fertiliser to the paddy fields,
making not only the rice but also the algae grow
faster, providing more food for the animals.
•
Many birds feed in and around the paddy fields.
Activity 4.2 .1
Habitats in an ecosystem
Choose one of the ecosystems shown in the photographs.
Use the internet to find out more about your chosen ecosystem.
Make a list of the different habitats in this ecosystem, and some
of the organisms that live in each of the habitats in your list.
Think like a scientist
L
Investigating a local ecosystem
You are going to investigate an ecosystem near your school.
For example, you could investigate:
•
a garden area
•
a group of trees
•
part of the playing field
•
a pond.
Safet y
You wi ll be working outside. It is important to stay in t he same area as t he rest
of your class. Always stay w ith a partner.
129 )
______
4_E_c_o_sy_s_t_e_m_s_ _ _ _ _ _ _ _ _ _ _ _)
Continued
You will need:
a selection of the apparatus and materials shown; choose what is suitable
for the ecosystem you are studying. These items are not drawn to scale.
This is a pitfall trap. This
one is made from a plastic
cup which has been set
into the ground as shown.
Small animals that crawl
or run over the surface
of the ground - such
as beetles - fall in and
cannot get out.
This is a sweep net. It has
a large net on the end of
a long pole. It is useful
for catching insects. You
can sweep it through long
grass. You can also use it
to catch organisms in a
pond or small stream.
It is important to check
your pitfall trap regularly.
If not, you may find
just one extremely fat
carnivorous beetle in it,
and nothing else.
You can use this
apparatus to find insects
living in the lower
branches of trees. Gently
hit a branch with the stick,
as your friends hold the
large piece of material or
a sheet underneath. If you
haven't got any material,
you can use an upsidedown umbrella.
,
=--- 1
A hand lens is useful for
looking at very small
organisms.
130)
A camera is useful for
taking photographs of
organisms, especially if
you do not know their
names. You can use your
photos to try to identify
the organisms later.
You can use books to try
to identify the animals
and plants that you find.
Quick identification keys
are also very useful.
4.2 Different ecosystems
Continued
It is important to remember that if you catch any animals, you must take great
care of them. Do not take them away from their habitat. Release them exactly
where you found them .
Method
1
Look all around the area you are studying. What kind of ecosystem is it?
Write a short description of it or draw a picture. For example: How big is it?
What kind of plants grow there? Is there a lot of light, or is it shady? Is it
damp or dry?
2
Find different habitats in the ecosystem. For example, if you are studying
a garden, habitats could include underneath stones, in the soil, on the
soil surface, on leaves, in flowers, on tree trunks and in the air.
3
Look for organisms living in each habitat. Make a list of them. If you don't
know their names, take a picture or make a drawing. You might find some
fungi, as well as plants and animals. If there are animals, what are they doing?
4
If possible, visit the ecosystem at different times of day - or even at night.
How does it change?
5
Draw a diagram to show some of the interactions you have seen between the
organisms, and between organisms and the non-living parts of the environment.
For example, if you were looking at a garden:
•
Did you see any insects visiting flowers?
•
Did you see any animals eating anything?
•
Did you find anything hiding from predators or the hot sun underneath
part of a plant?
•
Had anything made a burrow in the soil?
•
Did you see any decomposers?
It is important to remember that if you catch any animals, you must take great
care of them. Do not take them away from their habitat. Release them exactly
where you found them.
Method
1
Look all around the area you are studying. What kind of ecosystem is it?
Write a short description of it or draw a picture. For example: How big is it?
What kind of plants grow there? Is there a lot of light, or is it shady? Is it
damp or dry?
131)
______4__
E_co_s_y_s_te_m_s_ _ _ _ _ _ _ _ _ ____,)
Continued
Method
2
Find different habitats in the ecosystem. For example, if you are studying
a garden, habitats could include underneath stones, in the soil, on the soil
surface, on leaves, in flowers, on tree trunks and in the air.
3
Look for organisms living in each habitat. Make a list of them. If you don't
know their names, take a picture or make a drawing. You might find some
fungi, as well as plants and animals. If there are animals, what are they doing?
4
If possible, visit the ecosystem at different times of day - or even at night.
How does it change?
5
Draw a diagram to show some of the interactions you have seen between the
organisms, and between organisms and the non-living parts of the environment.
For example, if you were looking at a garden:
•
Did you see any insects visiting flowers?
•
Did you see any animals eating anything?
•
Did you find anything hiding from predators or the hot sun underneath
part of a plant?
•
Had anything made a burrow in the soil?
•
Did you see any decomposers?
Self-assessment
Read these statements, then assess yourself on how well you did the activity.
Give yourself:
0 if you did not try
1 if you think you did quite well
2 if you are quite pleased with how well you did.
•
I was careful to stay with the group and stay safe.
•
I made a good description or picture of the study area.
•
I found at least five different habitat s in the ecosystem .
•
I used at least two different methods to find organisms.
•
I found at least ten different kinds of organism.
•
I made a good diagram, showing interactions in the ecosystem.
If you gave yourself two marks for everything, t he best possible score
would be 12. How many marks have you given yourself out of 12?
If you did a similar investigation in future, how could you do it better?
132)
0
0
4 .2 Different e cosystems
Summary checklist
D I can describe some of the habitats and interactions in an ecosystem.
0 I can use different methods to find out about habitats and interactions in
an ecosystem near my school.
0
0
..c
..c
C
C
E
0
133 )
Ecosystems
4
)
> 4.3 Intruders in an ecosystem
In this topic you will:
•
learn about how new or invasive species can affect an
ecosystem
Getting started
Key Words
Work in a group of three.
eradicate
Think about the saguaro cacti in the Sonoran Desert.
Now imagine that someone brings a new species of cactus that
can grow and reproduce faster than the saguaro cactus.
What might happen to the saguaro cacti?
What might happen to some of the other species in the
Sonora n Desert?
Make a list of your ideas, ready to share.
extinct
native species
4.3 Intruders in an ecosystem
New species in an ecosystem
In your studies of ecosystems, you have seen how all the different
organisms interact with each other and their environment. In this topic,
you will find out what happens if a new species suddenly arrives. How
does the new species fit into the network of interactions? How does this
affect the species already there?
Introduced species in New Zealand
New Zealand is a country in the Pacific Ocean. New Zealand
became separated from all the other areas of land in the world
about 66 million years ago. Because of this separation, the
species that developed in New Zealand were different from
those elsewhere on Earth.
Before humans arrived in New Zealand, there were no predatory
mammals there. Many of the nath'e species of birds nest on the
ground. There were no predators to eat their eggs, so the eggs and
young birds were safe. Even the adults of several species of native
bird - such as the kiwi - cannot fly.
Nobody knows exactly when humans first arrived in New Zealand,
but it was probably about 700 years ago. Humans brought species of
animals with them that did not belong in New Zealand. For example,
rats stowed away on their boats. Rats now live in most of the country.
The rats eat birds' eggs and defenceless young birds.
Since then, other species have been introduced to New Zealand.
Farmers brought sheep, to farm for their wool and meat.
Rabbits were brought on sailing ships, to use as food. But the
rabbits escaped and began to eat grass in the sheep pastures.
So people brought stoats from Europe to control the rabbits.
Now stoats have spread all over New Zealand. They are
fierce hunters and breed rapidly. They can kill and eat birds
much larger than themselves. Stoats have made several species
of native bird extinct, including the laughing owl and the
New Zealand thrush. Stoats eat almost 60% of kiwi chicks.
People in New Zealand are now trying to eradicate (completely
get rid of) stoats, but this is very difficult to do. The best that can
be done is to control their numbers.
Scientists think that 53 species of native bird in New Zealand
have become extinct since humans arrived. The extinctions have
been partly caused by people hunting and killing the birds, but
mostly because of introduced invasive species.
135 )
______4__
E_co_s_y_s_te_m_s_ _ _ _ _ _ _ _ _ ____,)
Questions
1
In your own words, explain what a 'native species' is.
2
Name some native species in your own country.
3
Suggest why it is very difficult to eradicate an introduced species,
once it has settled into a new place.
Activity 4. 3.1
Why do some introduced species cause problems?
Stoats normally live in Europe. Stoats are not a 'problem animal' in the ecosystems
where they normally live.
1
With your partner, think of ideas to explain why stoats are such a problem in
New Zealand, but not a problem in their native countries.
2
When everyone is ready, share your ideas with the rest of the class. Make a
list of the ideas on the board.
3
Once all your ideas have been listed, work together with the rest of the class
to make a shorter list. For example, perhaps you can explain some of the
ideas more clearly if you use fewer words. Or perhaps two of the ideas are
really the same idea, and can be combined.
Questions
1
Buffelgrass is native to Africa, Asia and the
Middle East. It was planted in Arizona in the
1930s, as food for cattle. Now, it is spreading
rapidly through the Sonoran Desert.
What is the name for a plant, such as
buffelgrass, that is growing in an ecosystem
where it does not belong?
2
Buffelgrass grows in dense patches. It takes
water and nutrients from the soil.
Look at the picture that you made in Topic 4.1, showing interactions
in the Sonoran Desert. Suggest how buffelgrass could affect some of
the native species in the desert.
Summary checklist
D I can explain how new or invasive species can affect an ecosystem.
D I can describe examples of invasive species and their effects.
136)
0
4.4 Bioaccumulation
> 4.4 Bioaccumulation
In this topic you will:
•
find out about DDT
•
use a model to explain what happens to DDT in a food chain
•
learn what bioaccumulation is, and why it happens
Getting started
Think about what you learned about decomposers in Stage 7.
With a partner, answer these questions.
1
What is a decomposer?
2
What kinds of substance can decomposers break down?
3
What kinds of substance are decomposers unable to
break down?
accumulate
bioaccumulation
biomagnification
insecticide
persistent
toxic
______4__
E_co_s_y_s_te_m_s_ _ _ _ _ _ _ _ _ ____,)
DDT
DDT is an insecticide. This means that it
kills insects.
DDT was first produced in the 1940s. It was used
to kill insects that transmit diseases. It was
especially useful for killing mosquitoes that
transmit malaria, and fleas that transmjt a
disease called typhus. DDT was also used to
kill insects that eat crops.
No one thought that DDT could harm organisms
other than insects. This old picture was taken in
the 1940s. It shows a beach being sprayed with
DDT to kill mosquitoes. The people on the beach
are being sprayed, too.
DDT is very good at killing insects. But gradually, people began to
realise that it was also harming anin1als that no one wanted to kill.
In 1962, an American author called Rachel Carson wrote a book called
Silent Spring. She described how DDT was killing not only mosquitoes,
but also birds.
Her book made many people realise that some insecticides, including
DDT, are very harmful to the environment. Scientists now understand
how it causes harm to ecosystems.
DDT in food chains
We now know that DDT does not break down. It is a persistent
chemical. It stays in the environment for many years. It is not
broken down by decomposers.
When DDT is sprayed, some of it is carried
up high into the air. It can be blown for
very long distances, far away from where
it was used.
When DDT gets into an animal's body, it
stays there for the whole life of the organism it never breaks down.
DDT is very harmful to many kinds of animal.
lt is toxic (poisonous). For example, it makes
the shells of birds' eggs very thin and easy to
break. The old photograph in Figure 4.4.2
shows some eggs of a bird called an ibis. The
eggs did not hatch, because the female ibis
that laid them had DDT in her body.
138 )
,. ,
..
T
4.4 Bioaccumulation
Think like a scientist
Modelling DDT in a food chain
You will need:
•
at least 25 people to do this activity - it's even better with 30
•
at least 200 tokens, some blue, some yellow and some red
•
a stopwatch
•
a cup or small bag for each person, to put tokens in
•
1 card with 'eagle' written on it
•
several cards (about 8 in a class of 30) with 'small bird' written on them
•
more cards (about 21 in a class of 30) with 'insect' written on them.
•
one larger bag, big enough to hold all the cards
•
a method of marking out an area of ground outside, for example, traffic cones
(you could borrow something from the sports department, or you might be able
to use a marked-out part of a pitch used for sports)
•
a clipboard and paper so that someone (the teacher, or the eagle) can
record results
Method
1
Mark out an area big enough for people to run around. It could perhaps be
25 m by 25 m, but the exact size does not matter.
2
Spread all of the coloured tokens randomly in the marked-off area.
3
Put all of the cards into the large bag. Each person puts a hand into the bag
and takes one card.
4
Everyone takes a small bag, and then stands on the edge of the marked-off area.
5
One person (it could be your teacher) starts a stopwatch and says: 'Go!' Each
'insect' goes and 'feeds' in the area. They do this by picking up tokens and
putting them into their bags. Only one token can be picked up at once!
6
After 15 or 20 seconds, the timer shouts: 'Stop!' The insects stop feeding.
Each 'insect' counts the tokens in their bag. They count how many tokens
of each colour they have. The recorder writes down the results for each 'insect'.
7
The timer starts the stopwatch again, and the 'small birds' go and feed on the
'insects'. They do this by tapping an 'insect' on the shoulder. The captured
insect transfers their tokens into the small bird's bag. A 'sma ll bird' can only
eat one 'insect' at a time.
139 )
______
4_E_c_o_
s y_s_t_
e _m_s_ _ _ _ _ _ _ _ _ _ _ _)
Continued
8
After 15 or 20 seconds, the timer shouts: 'Stop!' The 'small birds' stop feeding.
The 'insects' (whether or not they have been eaten) move outside the marked
area. Each small bird counts the tokens in their bag . The recorder writes down
how many tokens of each colour each small bird has.
9
Now repeat steps 6 and 7, but this time the 'eagle' feeds on the 'small birds'.
10 Go back into your classroom . The recorder can now write all of the results
onto the board.
Questions
1
a
Calculate the mean number of red tokens that an 'insect' collected.
b Calculate the mean number of red tokens that a 'small bird' collected.
c
2
How many red tokens did the 'eagle' collect?
Copy and complete this 'food chain', using your results.
insects
... red tokens each
➔
small birds
... red tokens each
➔
eagle
... red tokens each
3
Explain why the mean number of red tokens that each animal has, increases
as you go along the food chain.
4
Now imagine that the red tokens represent DDT. What happens to the amount
of DDT in an animal's body, as you go up the food chain? Why does this happen?
5
In this activity, you modelled what happens to DDT in a food chain.
Do you think this is a good model of what happens in a real ecosystem?
Explain your answer.
Bioaccumulation and biomagnification
Imagine that DDT has been sprayed onto some water. Tiny algae take
up some of the DDT. Shrimps eat the algae, and fish eat the shrimps.
Cormorants (fish-eating birds) eat the fish.
All the DDT in all of algae that a shrimp eats over its lifetime
accumulates, or builds up, in its body. The longer the organism lives, and
the more DDT it takes in, the more DDT it gets in its body. This process
is called bioaccumulation.
All of the DDT in all of the shrimps that a fish eats accumulates in the
fish's body. Eventually, all the DDT in all of the fish that a cormorant
eats in its lifetime accumulates in the cormorant's body.
140)
4.4 Bioaccumulation
This means that the concentration of DDT in an animal's body
increases as you go up the food chain. This is called biomagnification.
The next diagram shows how the concentration of DDT in the bodies
of species in a food chain increases along the chain. The concentration
is measured in parts per million (ppm). This is the number of grams of
DDT in one million grams of the organisms.
cormorants
26.40 ppm
water
O.OOOOSppm
Cormorants
eat minnows.
~~
~
Questions
1
How many times greater is the concentration of DDT in a
cormorant's body than in a minnow's body?
2
Explain, in your own words, why the concentration in the cormorant
is greater than in a minnow.
People often get confused between bioaccumu lation and
biomagnification. How will you try to remember the difference
between them?
141)
______4__E_c_o_s_y_st_e_m_s_____________)
Activity 4.4.1
Biodegradable insecticides
Work in a group of three for this activity.
Some insecticides are biodegradable. This means that they can be broken down
by microorganisms in the environment, or inside an anima l's body.
Questions
In your group, discuss these two questions.
1
Do you think biodegradable insecticides show biomagnification?
Explain why.
2
Why doesn't everyone stop using DDT, and change over to using
biodegradable insecticides?
Be ready to share your ideas with the other groups in your class.
Summary checklist
0
I can explain what is meant by bioaccumulation.
D I can explain why DDT shows b ioaccumulation.
0
I can explain why organisms at the top of a food chain have higher
concentrations of DDT in their bodies than organisms at the base
of the food chain'
Check your progress
4.1 Tropical rainforests are very complex ecosystems.
Many different species live in a tropical rainforest.
Bromeliads are plants that grow in a
tropical rainforest. They often grow
on tall forest trees.
Bromeliads have spiky leaves arranged
in circles. They trap rainwater in their
centres. Small animals often live in the
little ponds in a bromeliad plant.
Use the photographs to describe two habitats in the tropical
rainforestecosystem.
[2]
Suggest the advantages to bromeliads of growing in their
particular habitat.
[2]
c
Suggest the advantages to the frog of living in their particular habitat.
[2]
d
Explain the difference between an ecosystem and a habitat.
[2]
a
b
4.2 Coral reefs are formed by tiny animals called coral polyps. Their hard
skeletons provide many different habitats where other species can live.
One of these species is a single-celled alga that makes a toxic substance
called ciguatoxin. Herbivorous fish eat the alga. Carnivorous fish eat the
herbivorous fish. Humans often eat the carnivorous fish.
a
Thousands of different species live on coral reefs.
Use the information to suggest why so many species can live there.
[2]
b
What is meant by a toxic substance?
[1 ]
c
Use the information to construct a food chai n.
[3]
______4__
E_c o_s_y_s_te_m
_ s _ _ _ _ _ _ _ _ _ _ _)
d
Ciguatoxin does not break down inside a fish that has eaten it.
Instead, it builds up in the head, liver and skin of the fish.
What is the name for this process? Choose one of these words.
bioaccumulation
e
ecosystem
[1]
poisoning
People who have eaten fish containing ciguatoxin can become very ill.
Suggest why eating a carnivorous fish is more likely to make you ill
than eating a herbivorous fish.
4.3 Winged loosestrife is a plant with purple
flowers. It grows in North America.
Purple loosestrife also has purple flowers.
It normally lives in Europe and Asia. It is
an introduced species in North America.
Both species of loosestrife are pollinated
by insects. After pollination, the flowers
produce seeds.
Scientists noticed that numbers of winged
loosestrife plants were decreasing in places
where purple loosestrife had been introduced. They did an experiment to
test this hypothesis:
When purple loosestrife is present, fewer winged loosestrife flowers
are successfully pollinated.
•
They grew plants of winged loosestrife in pots.
They also grew plants of purple loosestrife in pots.
•
When all the plants had flowers, the scientists arranged the pots in a field .
They used two different patterns.
0000
0000
0000
0000
e oe o
oe oe
e oe o
oe oe
Key
0
winged loosestrife plant
-
purple loosestrife plant
[2]
•
The scientists counted how many insects visited the flowers on each plant,
over a 15 minute period.
•
They left the plants in their pots until they produced seeds.
Then they counted how many seeds each plant produced.
Their results are shown in the table.
Arrangement of plants
Mean number of insect visits
per plant in 15 minutes
Mean number of
seeds per plant
winged loosestrife alone
35
80
winged loosestrife and
purple loosestrife
26
58
a
Explain what is meant by an introduced species.
[2]
b
Explain why the scientists used two different patterns, when they put
the plants in the field.
[3]
Describe how the presence of purple loosestrife affected the number
of insect visits to winged loosestrife.
[2]
d
Do the results support the scientists' hypothesis? Explain your answer.
[2]
e
Suggest two ways the scientists could improve their experiment.
Explain each of your suggestions.
[4]
C
Project
Project: Impact of an int roduced species
This project is about how people develop and use scientific understanding,
and how the uses of science can have a global environmental impact.
Your task
Work in a group of three or four.
You are going to investigate how a new or invasive species has affected
an ecosystem.
Use the internet to find an example of a species that has been introduced
into an ecosystem in your country.
Try to answer some of these questions.
•
Where does the species normally live?
•
Why and when was the new species introduced to your country?
•
How has it affected the ecosystems it has been introduced to?
•
Is it an invasive species? If so, why is it invasive in your country, but not
its native country?
•
Why did people not realise that the species might be a problem, when
it was first introduced? How has understanding improved over time?
•
Are people trying to eradicate or control the species? If so, how are they
doing this, and how successful are they? Is everyone happy about this,
or do some people want to protect the species?
Make a presentation about your findings,
ready to share with others.
Materials and
their structure
> 5.1 The structure of the atom
In this topic you will:
•
describe the structure of the atom
•
list the particles found in an atom
•
describe some of the properties of the particles found in
an atom
atoms
deflected
electrical charge
electrons
electrostatic
attraction
These three cups have been filled with water.
Would you expect these three cups to have:
a
exactly the same mass
b
masses that were nearly the same
c
masses that were very different?
Discuss this with a partner. Give reasons for your choice.
neutrons
nucleus
protons
sub-atomic
particles
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
Atoms
In stage 7 you learnt that atoms are so small that you cannot see them
without using the most powerful microscopes yet invented. The word
'atom' comes from a Greek word that means 'cannot be split'.
All the atoms of a particular element are the same. Different elements
have different atoms.
What is an atom like?
Scientists have discovered that atoms are made up of
even smaller particles, called sui).atomic particles. Atoms
are made up of three kinds of particles protons, neutrons
and electrons.
proton
--f---Q. . . . L__j__
neutron
The particles are arranged in a similar way in aJI atoms.
The protons and neutrons are grouped closely together
in the centre of the atom. They form the nucleus of the
atom. (Be careful not to confuse the nucleus of a cell
with the nucleus of an atom.)
~f
'
'
electron ~
The electrons move around the nucleus.
The three different particles in an atom have different
properties.
•
Protons and neutrons have much more mass than the electrons.
In fact, electrons have almost no mass.
Protons and neutrons have the same mass.
Protons have a positive electl'ical charge.
Neutrons have no electrical charge.
•
Electrons have a negative electrical charge.
There is a lot of empty space between parts of the atom. This space
really is completely empty - there is nothing in it at all.
There is an attraction between the positive and negative charges. This
electrostatic attraction between the positive charge on the protons and
the negative charge on the electrons is what holds individual atoms
together.
148 )
'
,
A helium atom
_j
nucleus
5.1 The structure of the atom
Quest io ns
1
Which particle has a positive electrical charge?
2
Which of the three particles has the smallest mass?
3
Which particles make up the nucleus of an atom?
4
The size of the negative charge of an electron is exactly the same
as the size of the positive charge on a proton. What is the overall
charge of the helium atom shown in the diagram?
5
How are the individual atoms held together?
How did scientists come up with this model of
the structure of the atom?
Scientists from many different parts of the world have worked on a
number of different ideas that have led to the model of the atom, that
they use today.
In the late 1890s a British scientist called J.J.Thompson discovered the
electron. His model for the atom was that the electrons were scattered
throughout the structure of the atom. It is sometimes called the 'plum
pudding model' because the particles are arranged randomly throughout
the model, like fruit in a cake or pudding.
-
- - positively
charged
matter
electrons
0
0
..c
..c
C
C
Thompson's model of the atom
E
0
149 )
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
One of Thompson's students was originally from New Zealand.
His name was Ernest Rutherford. Rutherford discovered the
proton in 1909 and the nucleus in 1911.
Rutherford's most famous experiment was the gold foil experiment.
In this experiment Rutherford fired fast moving particles, smaller
than an atom, at very thin gold foil. Most of the particles passed
straight through the foil. Only a few of the particles (about 1 in 8000)
were deflected in various directions. (Deflected means that the direction
of the particle was changed.)
particle source
-
gold foil
-
particle detector
Ernest Rutherford
particles that have
passed through the foil
Rutherfo rd 's gold foil experiment
The results of this experiment led Rutherford to have the idea
that the gold atoms must be mostly empty space, with their
particles packed into a dense nucleus at the centre. This helped
to move towards the model of the atom that scientists use
today.
Rutherford's model of the atom looked like this.
James Chadwick also worked with Rutherford and
Thompson. In 1932, he proved that neutrons exist. This
discovery moved the model of the atom closer to the one
scientists use today.
When scientists make a discovery, they write about what they
have done and what they think it means. Sometimes, if the
work is very complicated, many different scientists may be
involved. These different scientists can even be in different
countries, still working together. This is called collaboration.
Other scientists then look closely at the findings to see if they
can repeat the experiments and that if the discovery is true.
Some scientists actively look for mistakes in the work, or
whether the conclusions about the results are wrong. This is
called peer review.
Rutherford's mo del of t he atom
Tunnel in the Large Hadron Collider
150)
5.1 The structure of the atom
The sto1ies of these scientists show how people from all over the world
work together to develop their ideas. Each scientist builds on the ideas
and the discoveries of others. Chadwick, Rutherford and Thompson
won Nobel prizes for their work. Their experiments and ideas have
helped us to understand the
structure of the atom.
There is still a lot we do not know about atoms. Scientists continue to
work to improve our understanding of the structure of the atom. For
example, scientists from all over the world are using the Large Hadron
Collider in Switzerland to further understand the structure of matter.
Questions
Explain how Thompson's model of the atom is different from the
one scientists use today.
7 Who discovered the electron and when did they discover it?
8 Who proved that the neutron existed and when did they do this it?
9 What two things did Rutherford discover about the structure
of the atom?
10 How is Rutherford's model different from the model scientists
use today?
6
Activity 5.1.1
An atomic timeline
In a group of three, make a time line of the discoveries that have
led to the model of the atom we use today. Do some research on
the three scientists J. J. Thompson, Ernest Rutherford and James
Chadwick. Find out where and when they worked and some
personal details; add this to your time line.
How does the use of a model help me to understand the
structure of the atom?
Summary checklist
D I can describe the structure of the atom
D I can list the particles found in an atom
D I can describe some of the properties of the particles found in an atom
0 I can describe some of the discoveries that have helped to create the model
of the atom that is used today.
151)
______
s _M_at_e_r_ia_l_s_a_n_d_t_h_e_ir_st_r_u_ct_u_r_e______)
> 5.2 Purity
In this topic you will:
•
explain what is meant by purity
•
calculate percentage purity
•
describe how it is difficult to get a pure product
Getting started
Key words
Answer the three questions on your own and then check with a
partner. Be ready to share your answers with the class.
carat
suggest
1
What does it mean if a substance is pure?
translucent
2
Which of these items are pure substances?
sodium chloride; oxygen; sea water; gold; orange juice;
copper oxide; silver nitrate; soil; b lack ink; potassium.
3
Of the items in question 2, which are elements,
mixtures and compounds?
5.2 Purity
Pure elements
If an element is pure; it means that every one of
its atoms is exactly the same and made of just one
type of atom. For example, pure gold is made of
gold atoms. However, an alloy of gold may
contain other metals such as copper or silver.
When you buy gold it is usually marked to state
if it is pure gold (24 carat) or an alloy such as
18 carat or 9 carat. This is a measure of its
purity. The more gold it has, the higher its purity.
18 carat gold has 18 parts out of 24 that are
gold; the rest (6 parts out of the 24) is made up
of other metals such as silver or copper. 18 carat
gold has a purity of 75%. To calculate this:
M x 100 = 75%
24
The photograph shows samples of 8 carat, 14 carat, 18 carat, and
24 carat gold. You can see that the colour changes from slightly
coppery to yellow-gold.
When silver is sold, it is usually marked with the number of
parts per thousand that are silver. So, silver marked 925 has
925 atoms out of 1000 that are silver and 75 atoms of some
other metal. You can see this mark in the photograph of the
silver ring. Silver marked 900 is of lower purity than that
marked 925.
This silver ring has the mark 925.
The ring contains 925 parts silver out of 1000 parts.
?tio 100 92.5%
X
=
So, it is 92.5% pure silver.
153 )
______
s_M_at_e_r_ia_l_s_a_n_d_t_h_e_ir_st_r_u_ct_u_r_e______)
Diamonds are made from the element carbon. The carbon atoms are
arranged in a particular way. If they are pure, diamonds contain no
other elements. Pure diamonds are colourless and translucent (lets the
light through).
If diamonds have other elements mixed in with the carbon atoms, they
can be different colours. For example, .if a few carbon atoms per million
are replaced with nitrogen, the diamond will be yellow. If some carbon
atoms are replaced by atoms of the element boron, then the diamond
will be blue. The rarest of all is a green diamond, formed when one atom
per 1000 of carbon atoms is replaced by nitrogen, nickel or hydrogen.
A pure diamond
A yellow diamond
A blue diamond
A green diamond
Questions
1
What percentage of 9 carat gold is gold?
2
What percentage of silver is in silver marked 900?
3
Which element mixed with carbon in diamonds makes them blue?
4
Which elements may cause a diamond to be green?
154 )
5.2 Purity
Seawater
Seawater is made up of water and various
salts such as sodium chloride. If you
want to obtain sodium chloride from
seawater you can evaporate off the water.
In some countries this is done by letting
seawater fill flat and shallow areas called
beds, and allowing the water evaporate in
the heat from the Sun.
If you are trying to obtain pure sodium
chloride this will be a problem because
sodium chloride is not the only salt that
is dissolved in seawater. If you take I000 g W o rkers carryi ng salt in N ha Trang, Vietnam
of seawater, about 350 g of it is made up
of salts. Of this 350 g, about 68% is sodium chloride, the rest is made up
of magnesium chloride, sodium sulfate, calcium chloride and some other
salts. If you want pure sodium chloride, you need to do some work to
remove the other salts.
Salts are compounds made from acids. The names tell you which acid has
been used to form them. For example, sodium chloride from hydrochloric
acid and sodium sulfate from sulfuric acid.
seawater
salt from seawater
magnesium chloride 14.6%
sodium sulfate 11.4%
calcium chloride 3.1 %
other salts 2.9%
The sodium chloride that is obtained from this seawater is only 68%
pure. The mass of sodium chloride in 1000 g seawater is:
1l60 X 68 = 23.8g
Questions
5
Draw up a table to show the percentage of salts found in seawater.
6
What mass of magnesium chloride would you expect to find in the
seawater sample?
155 )
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
Think like a scientist
Finding the mass of salts in seawater
You will need:
• an evaporating basin
• safety glasses
• tongs
• Bunsen burner
• access to a top pan balance
• tripod
• pipe-clay triangle
• seawater sample
Method
1
Read through the method and think very carefully about any risks there may be
when you carry out this task. Write a risk assessment.
2
Place an evaporating basin on a top pan balance and record the mass.
3
Add some seawater and find the mass of the seawater.
4
Heat the seawater until it begins to spit. Remove
from the heat and allow the rest of the water to
evaporate.
5
When there is no longer any water remaining and
the basin is cool, find the mass of the salts.
Questions
FPO
1
What mass of salts did you obtain from the
seawater?
2
What percentage of the seawater is this?
3
About 68% of the salt in seawater is sodium
chloride. Estimate the mass of sodium chloride
in your sample.
4
Is this about what you expected? If not, why not?
5
What difficulties did you have carrying out this investigation?
How did you try to overcome them?
6
What safety measures did you have in place whilst carrying out this investigation?
Pure products
When a chemical reaction takes place and a product is formed from
the reactants, it is often very important that the product is pure. For
example when medicines are being made, the product needs to be free
from any impurities that may upset the way the medicine works or that
do the patient harm.
When there is a simple reaction there is only one product.
magnesium + oxygen ➔ magnesium oxide
156)
5.2 Purity
In other reactions there may be more than one product. When there
is more than one product they are mixed up together. These products
will need to be separated and purified to produce wh ichever pure
product you want. The products may also be mixed up with some of
the reactants if they have not all been used up in the reaction.
silver nitrate + sodium ch loride
➔
sodium nitrate+ silver chloride
sulfuric acid + sodium hydroxide
➔
sodium sulfate + water
barium chloride + sodium sulfate
➔
barium sulfate+ sodium ch loride
lead nitrate+ potassium iodide
➔
potassium nitrate+ lead iodide
copper carbonate+ hydrochloric acid
➔
copper chloride + water + carbon dioxide
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
Think like a scientist
Reactions with more than one product
You will need:
• safety glasses
• conical flask
• test tubes
• test tube racks
• measuring cylinder
• delivery tube with bung
• burette
• clamp stands
• universal indicator solution
• boiling tube
• safety glasses
• limewater
• chemical reactants as in the examples above
Safety
You must wear safety glasses to carry out all these reactions. Wash your hands
after handling any chem ica ls.
Method
Use the equations above as examples of chemical reactions you cou ld carry out.
You can try other reactions if your teacher prefers.
Remember than if you are going to do a
neutralisation reaction you will need to measure
the reactants carefu lly. Carry out a risk assessment
for each reaction you attempt.
Reaction 1
Silver nitrate is an irritant. Take care when you use it.
Half fill a test tube with silver nitrate solution. Place
some silver nitrate solution in a test tube and slowly
add some sodium ch loride solution.
Reaction 2
Sulfuric acid and sodium hydroxide are irritants take
care when you use them. Fill the burette carefully
using a small funnel.
sodium hydroxide and
,C....-- - -==--- .,., universal indicator
Your teacher may want to do this as a demonstration
as a burette can be difficult to use.
Place a measured 20cm3 vo lume of sodium hydroxide in a conical flask.
Add a few drops of universal indicator solution. Put sulfuric acid in the
burette and add to the flask until the alkali is neutralised.
Take care when you use the burette and ask for help if you have not
used one before.
158 )
5.2 Purity
Continued
Reaction 3
Barium chloride is harmful if swallowed.
Half fill a test tube with barium ch loride solution and add
sodium sulfate solution.
Reaction 4
Place lead nitrate in a test tube and
add potassium iodide. Wash your
hands after handling lead compounds.
Reaction 5
Copper carbonate is harmful so wash
it off you skin if you spill any.
+ - - - delivery tube
boiling tube
test tube
hydrochloric acid - - f -
Place a few spatulas of copper
carbonate in a boiling tube and add
coppercarbonate _ __,.,..~
hydrochloric acid. Place the delivery
tube bung in the mouth of the boiling tube and allow the gas to be
passed into water or limewater.
,~ -
limewater
C,
0
Questions
7
Record each reaction you carry out. For each one, write the word
equation and your observations.
8
For each reaction suggest or offer ideas on how the products
could be separated and purified.
9
What safety measures did you have in place whilst carrying out these reactions?
What does 'pure' mean? When chemical reactions take place
how can you be sure you have a pure product?
Summary checklist
D I can explain what is meant by purity
D I can calcu late percentage purity
D I can explain why it is difficult to obtain a pure product.
E
0
159 )
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_ st_r_u_ct u_re_ _ _ ____,)
> 5.3 Weather and climate
In this topic you will:
•
learn the difference between weather and climate
•
make observations of the weather
Getting started
With a partner, write down as many words about the weather as
you can. Be prepared to share them with the class. You must be
ready to explain the meanings of the words you write down.
atmosphere
climate
climatology
humidity
meteorology
statistics
visibility
5.3 Weather and climate
What is weather?
When you look out of the window, what is the weather like?
What people mean by weather is the state of the atmosphere and its
changes from minute to minute, hour to hour, day to day, or week to
week. In some places, the weather is very similar each day but in others
the weather changes frequently.
When people talk about the weather they say things such as, 'What is the
weather like today?', 'How hot is it today?' or 'Will it rain tomorrow?'
They are thinking in the short term.
People generally think about weather as the combination of temperature,
humidity, precipitation, cloudiness, visibility and wind.
Countries all over the world take careful measurements of the weather
to help predict what will happen next, to see patterns in the weather and
to provide information about the weather over time. For example, it is
important to be prepared for snowstorms or heat waves as they can affect
the transport systems, production of food, how much power people need
to run their homes, and even what they want to buy in the shops.
Scotland
Namibia
New Zealand
Canada
Republic of Ireland
Bang ladesh
161)
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
Questions
1
Describe the weather in each of the photographs. Use as many of
the words from the Getting started task as you can.
2
Why do scientists take careful measurements of the weather?
Activity 5.3.1
Recording the weather
In this activity you will record the details of the weather over a period of at least a week.
Method
3
In your group, d iscuss which weather features you will be able to measure and/or
observe. Share these ideas with the class.
4
After the discussion make a list of the weather features that you will measure and/or
observe.
5
Decide how your group will collect this information. What equipment will you need?
You may need to do some research to decide this. You may need some laboratory
equipment. A camera might also be useful as you could take photographs to record
cloud cover.
Remember that the readings should be taken at the same time each day.
The temperature should be taken in the shade, not in full sun. The bulb of the
thermometer should not be touching anything other than the air.
6
Prepare a results table to record your findings.
7
Record your findings each day for at least a week.
Questions
1
Why shou ld the readings be taken at the same time each day?
2
Why are the temperature readings always taken in the shade?
3
Write a report about the changes in the weather over the week. In this report you
should present your observations in an appropriate way.
4
Plot a graph to show the changes in temperature over the week.
5
Compare your readings with someone else in your class. Are there any differences
and, if so, can you give reasons for the differences? Is this comparison a fair
comparison?
6
Compare your readings with those that are recorded nationally. You could use the
internet to find these. Are yours different and, if so, explain why yours are different.
Is this comparison a fair one?
162 )
5.3 Weather and climate
Activity 5.3.2
Finding out about the weather.
In this activity you will find out information about the weather in a particular
place and evaluate the information you find .
1
Work with a partner. Choose a particular place anywhere in the world.
Perhaps it is somewhere you might like to go on holiday, to have a beach
holiday, to go skiing or to learn how to sail a boat.
2
Find as much information as you can about the weather in that place.
For example: you may need to know: What is the average number of hours
of sunshine? How much rain is expected? How windy is it? How much snow
there will be?
Make sure you find information from different sources. You might look at
web sites such as; travel agents, the national weather information or local
weather watchers. You could also look at past weather records over a few
years and compare them.
3
4
Think about these questions and discuss them with your partner.
•
Is the information you find from all sources exactly the same?
•
Can you suggest why this is?
•
Which source of information do you think is more reliable?
•
Could some sources be biased? Perhaps someone wants to give the best
view of the weather to encourage you to go there.
Present your findings, as a poster or a talk, and suggest the best time of year to
visit your chosen p lace. Use the suggested questions as a starting point to explain
which sources of information you have used and how much you feel able to trust
the information.
How can I explain the difference between the weather and the
climate where I live?
163 )
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_ st_r_u_ctu_re_ _ _ ____,)
Weather or climate?
What is the difference between weather and climate?
When people talk about climate, they mean the weather of a place over a
much longer time, usually more than 30 years. Weather can change in a
few hours or even in minutes.
Climate is the average weather in an area and takes several years
to change. Climate information includes the statistics of weather
information that tells us about the normal weather as well as the range
of extreme weather at that place.
Weather is affected by factors such as temperature, humidity, cloudiness
and precipitation.
Climate is affected by two key factors: temperature and precipitation.
The study of weather is called meteorology.
The study of climate is called climatology.
Climate zones
The map below shows the main climate zones on Earth. The key shows
the names of these zones.
Key
□ polar
,.r. ;--1~
,•
I iot
r ,.,..4
...)l ".,..
'
I
•
~
~
....
--------
"?
~ - - - -~ = = ~ - - - - - - - - - - - - - -
164)
,,
/
■ tundra
■ mountains
■ temperate
■ mediterranean
arid
■ tropical
5.3 Weather and climate
Each zone has a characteristic climate.
Climat e zone
Description of climate
Polar
very cold and dry all year
Temperate
cold winters and mild summers
Arid
hot and dry all year
Tropical
hot and wet all year
Mediterranean
mild winters and hot, dry summers
Mountains/tundra/taiga
very cold all year
Questions
3
Which climate zone do you live in?
4
Name two countries that are in the arid zone. (You may need to use
an atlas to help you.)
5
Name two countries that have areas with a Mediterranean climate
but are not near the Mediterranean Sea.
6
Name three countries that are in the tropical zone.
7
What is the difference between the climate in the arid zone and the
tropical zone?
8
What are the differences between the climate in the temperate zone
and the Mediterranean zone?
What do I notice about how the climate zones are distributed?
Summary checklist
D I can explain the difference between weather and climate
D I can make observations and take measurements of the weather
165 )
______s_M_at_e_r_ia_ls_a_n_d_th_e_ir_st_ru_ct_u_re______)
>5.4 Climate and ice ages
In this topic you will:
•
learn about how the Earth's climate has changed in past
•
find out about ice ages, glacial periods and interglacial
periods
•
look at some of evidence that the Earth's climate cycles
between colder and warmer periods.
Getting started
Key words
The photgraph shows the body
of a baby mammoth, which has
been named Yuka. Her frozen
body was discovered in 1977
in eastern Siberia. In that part
of the world, it is so cold that
the lower layers of the soil stay
frozen solid all year round.
Scientists think that Yuka lived
and died about 39000 years ago, when the temperature was
even colder than it is now.
boulder
With a partner, discuss why Yuka's body has been preserved for
so long. Be ready to share your ideas with the rest of the class.
cycled
glacial period
glaciers
ice ages
interglacial period
peat bog
5.4 Climate and ice ages
Ice sheets
Look back at the photograph in the Getting started section. When Yuka
was alive, and for thousands of years afterwards, the Earth was much
colder than it is now. The map shows the parts of the world that were
covered by ice sheets 25 000 years ago.
Key
D icesheet
Activity 5.4.1
Where in the World is there ice?
Working in a group of three or four, use an atlas to find out which
parts of the Earth are covered with ice today.
Compare this with what the Earth looked like 25000 years ago.
Be ready to share your ideas.
Questions
5
Name a part of the Earth that was covered with ice 25 000
years ago, but is no longer covered with ice.
6
When you look at the parts of the Earth that are covered with
ice today what do they have in common?
167 )
______
s_M_
at_e_r_ia_l_
s_a_n_d_t_h_e_ir_ st_r_u_c_tu_r_e______)
Glacial and interglacial periods
The very cold period when Yuka lived lasted until
about 10 000 years ago. Because so much of the
Earth was frozen, it is called a glacial period.
'Glacial' means 'frozen'. Today, the Earth is in an
interglacial period. 'Inter' means 'between'. Over the
last 450,000 years, the Earth's climate has cycled or
swung between glacial and interglacial periods.
- ----------------
In an interglacial period, there is permanent ice
close to the North and South Poles.
•
In a glacial period, the ice spreads much further
south from the North Pole and further north
from the South Pole.
Wh en Yuka w as alive, t he Earth was in a glacial perio d .
M uch m ore o f the Earth w as frozen t han now.
Ice ages
Looking even further back in time, scientists have found that this cycle
of glacial periods and inter-glacial periods did not always happen. There
were long periods of time when Earth was so warm that there was no
permanent ice on its surface, not even at the North Pole or South Pole.
In between these warm periods, there were cold periods, with glacials and
interglacials. T hese cold periods are called ice ages.
The graph in below shows when scientists think the ice ages happened
on Earth. They think the second one, which began about 850 million
years ago, was the coldest. Some scientists think that the whole Earth was
covered with ice and snow then. The Earth was like a giant snowball.
ice age
25
20
Average g lobal
temperature 15
in °C
10
ice ice
ice age age age
~ t
l
ice age
t
l
~
.... .........
~
'
5
2500
5'
2000
1500
1000
Millions of years ago
500
today
0
Temperature
at a site a Iittle
North of the
_
5
South Pole in °(
interglacial
periods
glacial
periods
400000 300000 200000 100000 today
Years ago
168 )
5.4 Climate and ice ages
Questions
1
How many ice ages do scientists think there have been on Earth?
2
Is the Earth in an ice age now? Explain why you think that.
3
Explain the difference between a glacial period and an ice age.
4
Is the Earth in a glacial period now?
How do scientists know the Earth
was colder in the past?
The photograph shows some boulders (big rocks) in
California, USA. People have often wondered how
rocks like this got into their strange positions. The
best explanation is that they were carried there by
ancient glaciers. Glaciers are rivers of ice that move
slowly downhill (they are formed from snow that over
many years becomes compressed into thick masses of
ice). The glaciers carry rocks with them. If the glacier
melts, the rocks are left behind. Sometimes, scientists
can see scratches on the rock surfaces, where the
moving ice dragged other rocks across them.
These rocks are in Yosemite National Park, in California.
Scientists think they were left behind when a glacier
melted, thousands of years ago.
Boulders like this were the first clue that glaciers
used to be present in parts of the Earth that are
much warmer now. Later, other evidence was found
that supports this idea. For example, in places that
are now quite warm, it is possible to find fossils of
animals and plants that were adapted to live in very
cold places.
Questions
5
Use an atlas or the internet to identify and list
glaciers nearest to where you live.
6
When rivers run through rock, they wear the
rock away. This sometimes creates very deep
valleys, such as the Grand Canyon in Arizona.
When glaciers moved millions of years ago,
they left their mark on the landscape. Find out
about and describe the effect that glaciers had
on the land.
A glacier in Iceland
169 )
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_ st_r_u_ctu_re_ _ _ ____,)
Pollen evidence for glacial and
interglacial periods
Scientists can use pollen to find out what kind of plants lived long ago.
In New Zealand, a scientist extracted a core of soil from a peat bog.
When plants die they normaJly decay. In some conditions, without
oxygen and slightly acid, the decay is very slow and a peat bog may
be formed. The different layers of peat represent different periods of
history, the deeper the peat, the older it is. Scientists can take samples of
the peat bog by using an instrument called an auger and remove a core
of the peat bog. They must be careful to remove the core and keep it in
the correct order so that they know which part is oldest.
This scientist is using an auger to
extract a core sample.
A core sample from a peat bog showing d ifferent layers.
The deepest level of the soil in the core was formed 237 000 years
ago. The scientist collected pollen from different parts of the core.
He identified the plants from which the pollen came. Because he knew
the type of climate that each kind of plant can live in, he was able to
work out what the climate was like between years ago and now.
170)
5.4 Climate and ice ages
Depth (cm) Core
Years ago
Environment
Climate cycle
0
100
200
mainly lowland forest
t
interglacial
Climate warms, ice retreats,
lake becomes a bog.
•
•
300
cold climate, subalpine vegetation
400
500
t
t
600
700
Warm climate forest expands.
interglacial
cold climate vegetation
with glacier nearby
g lacial
800
900
glacial
Climate cools,
grassland increases, forest decreases.
1000
Summary checklist
D I can describe how the Earth's climate has changed in the past
D I can explain the difference between ice ages, glacial and
interglacial periods
D I can give some evidence that the Earth's climate cycles between
colder and warmer periods.
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_ st_r_u_ct u_re_ _ _ ____,)
> 5.5 Atmosphere and climate
In this topic you will:
•
learn about the atmosphere of the Earth
•
learn how a change in the atmosphere can affect the climate
•
learn about renewable resources
Check your understanding
What is an ice age? What evidence is there to show that the
Earth's climate was different in the past?
Think about the two questions. Write down your ideas. Then
discuss them with a partner. Together sort your ideas out and be
prepared to share them with the class.
words
analogy
biodegradable
bioplastics
deforestation
emissions
fossil fuels
global warming
greenhouse effect
locked up
photosynthesis
recycled
renewable
resources
5.5 Atmosphere and climate
The atmosphere
The atmosphere is a layer of gas
above the Earth's surface. It is very
different today fro m the atmosphere
when the Earth formed billions of
years ago.
Earth's
atmosphere
Scientists think that the Earth was
formed about 4600 million years
ago. The Earth was very hot and it
was molten for millions of years. Then, as the Earth cooled, a solid
crust formed. There was a lot of volcanic activity, much more than
there is now. The volcanoes produced gases, which formed the early
atmosphere. Water vapour was produced by the volcanoes and, as the
Earth cooled, this water vapour condensed into liquid water. The water
fell as rain and formed the first lakes and oceans.
About 4000 million years ago, scientists think that the atmosphere
contained mainly carbon dioxide, little or no oxygen, small amounts
of the gases methane and ammonia, and some water vapour. This early
atmosphere on Earth was like the atmosphere on Venus is today. The
temperature on Venus is very high - on the surface, it is which is hot
enough to melt lead.
Earth's early atmosphere
4% -------,,,-<~i:i=::::::,,,..,__ _ traces of
water vapour
nitrogen,
ammonia,
methane
Earth's atmosphere today
-ii=:::,,,.~- - tracesof
carbon dioxide,
water vapour,
ammonia,
methane
21%
oxygen
95%
carbon dioxide
nitrogen
average surface temperature
above 400°(
average surface temperature
20°c
78%
Questions
1
Where did the early atmosphere on Earth come from?
2
Give at least two differences between the early atmosphere on
Earth and the atmosphere today.
3
Explain why the Earth's early atmosphere was not suitable for
us or any other animals.
173 )
______
s_M_
at_e_r_ia_l_
s_a_n_d_t_h_e_ir_ st_r_u_c_tu_r_e______)
Changes to the atmosphere
About 3500 million years ago, micro-organisms
developed on Earth. They lived in the oceans and
used the carbon dioxide in the atmosphere to make
food. They produced oxygen as a waste product of
this process. As plants developed over millions of
years, they began to grow on land. Plants use
carbon dioxide to produce food (glucose, a sugar)
by the process of photosynthesis.
carbon dioxide +water ➔ glucose+ oxygen
The levels of oxygen in the atmosphere continued
to rise. Scientists know this because there was
enough oxygen to combine with iron in the rocks
to form iron oxide.
These rocks in Dalio, Ethiopia have bands of red iron
oxide and date from about 2.1 to 2.0 billion years ago.
By 200 million years ago there was very little carbon dioxide left in the
atmosphere. Most of the carbon had been used to make the chemicals,
which are part of all living things.
When the organisms die and rot, the carbon in them is released back
into the environment. It is recycled. Some organisms do not rot when
they die and are turned into fossil fuels such as oil or coal. The carbon is
locked up in the fossil fuels until they are burned them.
Many organisms with shells evolved around 600 to 400 million years
ago. The shells are made from calcium carbonate, CaCO3 • When these
shelled animals died and fell to the bottom of the oceans as sediment the
many layers of shells pressing down on each other formed rocks, such as
limestone. So carbon is also locked up in these rocks.
Fern fossil in coal
174 )
This limestone is full of foss ils of animals with shells.
5 .5 Atmosphere and climate
Questions
4
What are fossil fuels?
5
How did the carbon dioxide in the atmosphere get used up?
6
What evidence is there that the levels of oxygen rose?
7
What two elements are present in carbon dioxide?
8
What three elements are present in calcium carbonate?
9
Limestone is a sedimentary rock. How is it formed?
10 When did carbon first start to be locked up?
Atmospheric changes today
The amount of carbon dioxide in the atmosphere fell until about
200 years ago. Then the levels of carbon dioxide began to rise. Where
is the carbon dioxide coming from? Humans caused this rise because
they started to release the carbon that had been locked up in the Earth
for millions of years. They burn fossil fuels, such as oil and coal, to
keep themselves warm.
carbon+ oxygen ➔ carbon dioxide
As humans developed industry and transport, they have burned more
and more oil and coal. So there are greater emissions of carbon dioxide.
Humans use a lot of fossil fuels to generate electricity in power stations.
A container ship burning d iesel
Brick factories producing waste
gases from fossil fuel
Cars burning petrol
175 )
______
s_M_
at_e_r_ia_l_
s_a_n_d_t_h_e_ir_ st_r_u_c_tu_r_e______)
Humans also make the situation worse as they cut down forests of large
established trees that use a lot of carbon dioxide in photosynthesis. This
deforestation is done for many reasons: to use the wood for building or
to make things, to get to resources such as minerals which are mined, to
produce crops for profit such as palm oil, to grow more food crops, or to
provide pastures for animals such as cattle. Because there are fewer trees,
less of the carbon dioxide is being used up, so the level in the atmosphere
increases. Cattle eat the grass and produce carbon dioxide and gases such
as methane in their i11testines. This also changes the atmosphere.
This forest is being cut down to
provide wood.
Many of the trees in this forest have been
cut down to grow palm oil plants
This forest is being cut down to p rovide
more land for agriculture.
When limestone, which consists of calcium carbonate, is used to make
other products such as building cement, the carbon in the calcium
carbonate is released into the atmosphere.
calcium carbonate ➔ calcium oxide+ carbon dioxide
A ll these things lead to a change in the atmosphere and an increase in
carbon dioxide levels.
Atmospheric changes and climate
There is evidence that the carbon dioxide and other gases, such as methane,
act like a blanket around the Earth. This is an analogy. The 'blanket'
represents the gases that keep the Earth warm. Another analogy is that the
gases are like putting the Earth in a greenhouse. A greenhouse lets in light
and heat from the Sun, but heat energy is trapped inside.
176 )
5.5 Atmosphere and climate
Think about how an analogy can help you to understand
an idea?
The layers of gases produce the greenhouse effect. This is a natural
effect; without it, the Earth would be much colder. However, increasing
the levels of greenhouse gases, such as carbon dioxide, methane and
water vapour, increases the greenhouse effect. So, as the levels of
carbon dioxide, methane and water vapour increase, the amount of heat
escaping decreases, and so the Earth's climate becomes warmer.
This is known as global warming.
atmosphere
Earth
Sun
177 )
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
Think like a scientist
The greenhouse effect
You will need:
•
three large plastic bottles, such as 2 litre drinks bottles with lids,
with a hole in each lid
•
three thermometers
•
a means of fixing the thermometers in p lace (such as modelling clay)
•
carbon dioxide supply
'[
thermometer
modelling clay
i
plastic bottle
extra carbon dioxide
extra water
normal air
Method
1
Place a thermometer in each of the bottles so that the bulb does not touch
the bottle in any way.
2
Add some carbon dioxide to one bottle.
3
Add about 5 cm 3 of water to another bottle.
4
Leave the th ird bottle with normal air.
5
Label the bottles.
6
Place the bottles alongside one another outside. If this is not possible,
you can leave them in the classroom near the window.
7
Take the temperatures in each bottle at the start.
8
Record the temperatures in the three bottles over the next few days.
You decide when and how often.
178 )
5.5 Atmosphere and climate
Continued
Questions
1
What did you consider when deciding when and how often to take readings?
2
Present your findings in a table.
3
What do your results show?
4
Why did you have one bottle with normal air in it?
5
Can you explain why you got these results?
6
How could you improve the investigation?
Reducing global warming
You have seen that humans contribute to global warmjng by burning
fossil fuels. One way to reduce this impact is to use renewable resources.
A renewable resource is one that does not deplete (run out) or can be
replenished within a human's life time. Examples include wind, tidal and
solar power.
A non-renewable resource is a resource that cannot be replaced after it is
used. Examples include coal, petroleum, and natural gas.
Renewable resources
When fossil fuels are burned to generate electricity, carbon dioxide
is produced. This adds to the problem of global warming. The more
electricity is produced, the more carbon dioxide adds to the problem. To
reduce global warming people need to generate more of their electricity
from renewable energy resources. These energy resources will become
more important as the supplies of fossi l fuels run out.
179 )
______
s_M_at_e_r_ia_l_s_a_n_d_t_h_e_ir_st_r_u_ct_u_r_e______)
Wind
People have been using the power of the wind for hundreds of years.
They used windmills to grind wheat into flour and to pump water.
Now they use wind turbines to generate electricity. You need a lot of
wind turbines to generate as much electricity as a power station so
wind turbines are grouped together to form wind farms. No harmful
waste product, such as carbon dioxide, is produced when electricity is
generated in this way. The problem with wind-generated power is that
electricity is onJy produced when the wind blows.
This w indmill in France was used to
This wind pump is used to pump water
This w ind farm, made up of many wind
grind wheat.
on this farm.
turbines, is used to generate electricity
in China.
Tidal
Tides make water rise and fall twice every day.
This happens as a result of the pull of the Moon's
gravity as the Earth spins. It is possible to use this
movement to generate electricity. To do this you
need to trap the water, in river estuaries, behind
a barrier and then generate electricity by releasing
the water to flow through electricity generator
turbines as the tide goes out. The problem is you
can only generate electricity at certain times
A hydroelect ric t urbine at a tidal farm in Brest,
each day and the barrier may interfere with
North West France
wildlife habitats.
- - - - - - - - - - - - - - -- -
Solar
The energy from the Sun can be used to generate
electricity. Photovoltaic cells can convert solar
energy to electrical energy. This can only happen
when the Sun is shining.
These photovoltaic cells are part of a large solar energy farm
in Mexico.
180)
5.5 Atmosphere and climate
Using other renewable resources
Bioplastics
The use of plastics has developed over the
past hundred years. Plastics are very useful materials but they have
one very big problem: they do not break down easily and cause many
problems for wildlife when they are thrown away. The waste builds
up on land and in the oceans. Humans produce a lot of plastic waste,
especially from plastics that are only used once.
Bioplastic is a biodegradable material that comes from renewable
sources (biomass, such as vegetable oils, sawdust or food waste)
unlike conventional plastics that are made from petroleum .
•
Plastic waste on a beach in Indonesia
a
This cutlery is made from biodegradable bioplastic.
The use of bioplastics from renewable sources will help to reduce the
use of fossil fuels and to prevent damage to the environment caused
by disposal of single-use plastics.
What can I do to reduce my use of single-use plastics?
Summary checklist
D I can describe how the Earth's climate has changed in the past
0 I can explain the difference between ice ages, glacial and
interglacial periods
0 I can give some evidence that the Earth's climate cycles between
colder and warmer periods.
181)
5
M aterials and t heir structure
Check your progress
5.1 a
Copy the diagram of a helium atom and label it, using these labels.
proton
neutron
electron
nucleus
'
''
''
[4]
b
Name the subatomic particle that:
has a positive charge
[1]
11
has no charge
[1]
iii
has the least mass
[1]
iv
is made up of protons and neutrons
[1]
5.2 Gold jewellery is marked to tell you how pure the gold is.
Which is the marking that has the most gold?
a
15 carat gold
b
9 carat gold
C
18 carat gold
5 .3 Pure diamond is made up of carbon atoms arranged in a particular way.
How do pure diamonds differ from diamonds that contain other elements?
[1]
5 .4 Match the terms, A-E, with the meanings, 1-5.
[5]
A weather
1 a measure of the amount of water vapour in the
atmosphere
B climatology
2 the state of the atmosphere in a particular p lace
C climate
3 the study of weather
D meteorology
4 the weather conditions prevailing in an area in
general and over a long period
E humidity
5 the study of climate
5.5 The graph shows the average global temperatures over the past 400 million years.
.,.
25
I
20
-
~
~ '/
~
.l
.-P..
--~ -~
\
Average global
temperature in °C
~~
15
~~
=1
10 .........
\
~
'I I
I
.
.
I
I
5
400
I I
300
200
100
today
Millions of years ago
What was the average global temperature between 350 and 260 million
years ago?
[1 ]
b
What is this period of time known as?
[1 ]
c
What was the average global temperature 100 million years ago?
[1 ]
a
5.6 How does the study of ice cores from deep in the ice, from places that have
been frozen for a long time, such as Greenland, help us to understand
how our atmosphere has changed over time?
[2]
5.7 What evidence is there that the Earth is getting warmer?
[2]
5.8 The atmosphere has changed since the Earth formed.
For each of these statements write true or false.
a
The atmosphere now has more carbon dioxide than the earlier atmosphere
[1 ]
b
The early atmosphere had little or no oxygen
[1 ]
C
The atmosphere was formed from the gases produced by volcanoes
[1 ]
d
The atmosphere today contains about 50% nitrogen
[1 ]
e
The atmosphere today contains about 0.04% carbon dioxide.
[1 ]
Much of the electricity you use is generated using fossil fuels.
Name three ways electricity can be generated without using these fuels.
[1 ]
b
What is meant by the term 'global warming'?
[2]
C
Explain how using fossil fuels adds to the problems of global warming.
5.9 a
5.10a
What is an analogy? Give an example.
[2]
______s__M_a_t_e_ri_al_s_a_n_d_t_h_e_ir_st_r_uct_u_re_ _ _ ____,)
Project: Global warming and climate change debate
Background
In June 2019, the average world temperature was. It was an increase of 1.1 °C
above the average global temperature for the whole of the twentieth century.
During th is worldwide heat wave there were:
•
wildfires in the Arctic with millions of hectares burning in Northern Russia
•
heat waves and severe water shortages in India
•
more than 5000 people in Japan taken to hospital for treatment due to the
heat wave
•
a huge impact on the growth of crops.
July 2019 was the hottest on record in Europe. People died of heat stroke.
Overhead power cables expanded in the heat and failed. Crops were damaged
so food production was affected.
Scientists say it is the latest sign that the Earth is experiencing a huge increase in
global warming. There is a wide sense amongst scientists that the rise in carbon
dioxide emissions from human activities is altering the temperature. A climate
researcher from the European Union's Copernicus Climate Change Service, said
in a television interview:
'This particular month has been very warm, but to me this is not the main point.
All the months of 2019 have been warm in comparison to other years. And that
trend is not likely to stop unless we do something about reducing the emission of
greenhouse gases.'
However, some people think that the change in temperatures is just part of the
Earth's normal cycle and there is no need to reduce the emissions of greenhouse
gases as there is no proof it is these gases that cause climate change.
Your task
In your group (no more than four), draw up two lists of evidence and give your
reasoning; one in support of the idea that humans are contributing to climate
change and one that does not support that idea.
Your teacher will select which point of view each group will represent. During
the debate your group must stick to the point of view you have been given.
I"
----~~__ J_________
Light
> 6.1 Reflections
In this topic you will:
•
describe how light is reflected from a plane surface
•
understand the law of reflection
•
be able to draw ray diagrams to show reflection of light.
Getting started
Work in groups to discuss answers to these questions.
1
Does light travel in straight lines or in curved paths?
2
Describe the evidence to support your answer to question 1.
angle of incidence
angle of reflection
incident ray
law of reflection
normal
perpendicular
p lane mirror
protractor
ray diagram
rays
reflection
set square
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Reflection
When you think of reflection you probably think of using a mirror.
Most of the mirrors you use are plane mirrors. 'Plane' means flat.
To see what reflection looks like from a surface that is not plane,
you can look at your own reflection from a spoon. The reflection
is distorted.
Remember that light travels in straight lines called rays. When drawing
light rays, always use a ruler and put an arrowhead on the ray to show
its direction.
A light ray arriving at a mirror is caJJed an incident ray. An incident ray
is the ray coming onto a surface.
The incident ray makes an angle with the surface of the mirror. Measure
this angle from a line perpendicular to the mirror and not from the mirror
itself. The line perpendicular to the mirror is called the normal. In physics
and maths, 'normal' means perpendicular or at right angles to something.
The diagram shows how to do this.
1. Draw the incident ray and the mirror. Sometimes,
this is done for you.
1
inciden~
ray
ITIT/7T/7TIT/7TIT/7TITITIT7//J//7 mirror
2. Use a ruler to make the incident ray meet the mirror.
2
inciden~
ray
1/IT7/TITITl7TIT/7 mirror
3. Use a protractor or set square to draw the normal.
3
normal
4
normal
The normal is perpendicular to the mirror where the
incident ray meets the surface. The normal is usually
a dashed line so it is not confused with the light ray.
4. Use a protractor to measure the angle between the
incident ray and the normal. We call this angle the
angle of incidence or???.
5. Measure an angle equal to the angle of incidence
on the other side of the normal. This angle is ca ll ed
the angle of reflection or???. Draw a reflected
light ray coming away from the mirror at this angle.
Remember to put an arrowhead on the reflected ray.
186)
6.1 Reflections
These diagrams are called ray diagrams
because they show what happens to the
light rays during reflection.
What we have drawn obeys the law of
reflection. Which is that the angle of
reflection is equal to the angle
of incidence.
In physics, a law is something that
always applies.
We can use the law of reflection in
everyday situations.
For example, mirrors can be used to
see behind us.
The d river of t he car can see t he cyclist by using t his mirror.
In this picture, light from the Sun is reflected from the cyclist. Th is is the
incident ray on the mirror. The reflected ray from the mirror goes to the
driver's eye.
The ray diagram shows how this works.
187 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Questions
1
Which of the angles in this diagram is the angle of reflection?
Write the letter.
mirror
2
Copy this ray diagram.
a
Extend the incident ray to meet the mirror.
incident"'-
ray
~
b Draw a normal where the incident ray meets the mirror.
3
c
Measure and write down the angle of incidence.
d
Draw a reflected ray in the correct place.
Sofia looks at a candle in the mirror.
Copy and complete the diagram to show how light
from the candle reflects from the mirror to Sofia.
You do not have to measure the angles.
Draw and label:
•
the incident ray
•
the reflected ray
•
the angle of incidence,
. the normal
. the angle of reflection,
4
Marcus drops a pencil. The pencil rolls under his bed.
Marcus cannot see the pencil.
The diagram shows a light ray coming from the pencil.
Marcus can use a mirror to see the pencil.
Copy and complete the diagram by adding a mirror and a
reflected light ray to show how Marcus can see the pencil.
You do not have to measure the angles.
188 )
Marcus
....11
6.1 Reflections
Activity 6.1 .1
Mirrors and reflections
Work in pairs.
Make a list of places where mirrors are used.
In each of your examples, describe why a mirror is used.
Reflections can also be seen from some surfaces that are
not mirrors.
Make a list of some of these surfaces.
What do these surfaces have in common?
Think like a scientist
Measuring angles of incidence and reflection
In this investigation, you will investigate the law of reflection.
Work in pairs or groups of three.
You will need:
• Make the room as dark as possible for this activity.
• p lane mirror and support to hold it vertical
• ray box with power supply
• plain paper
• pencil
• ruler
• protractor
Method
1
Set up the equipment as shown in the diagram.
mirror
modelling clay
white paper
to power
supply
----
2
Place the p lane mirror vertically at one side of the white paper.
Mark the position of the front of the mirror on the paper using
a pencil.
Continu ed
189 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Continued
3
Place the plane mirror vertically at
one side of the white paper. Mark
the position of the front of the
mirror on the paper using a pencil.
4
Use the protractor to draw a
normal line at the surface of
the mirror.
5
Use the ray box to direct a ray of
light onto the mirror. Where the
normal meets the mirror surface.'
6
Use a pencil to make marks on
the paper for the positions of the
incident and reflected rays as
shown in the diagram.
7
Turn the ray box off, remove the mirror and use the pencil marks to construct
a ray diagram. Use the protractor to draw the normal.
8
Measure the angle of incidence, i and the angle of reflection, r from your
diagram and record the angles.
9
Repeat this for at least four more different angles. Use a new piece of paper
or a new area on the same piece of paper each time.
Questions
1
Record your results in a table with two columns: angle of incidence and
angle of reflection. Remember to include the unit.
2
State:
a
the independent variable
b the dependent variable in this experiment.
3
Draw a graph of your results. Put the independent variable on the x-axis.
Complete your graph with a straight line of best fit.
4
Describe the pattern in your results.
5
a
Describe some of the things that were difficult to do accurately in this experiment .
b
Suggest some ways to improve the accuracy of this experiment.
190)
6.1 Reflections
Continued
Self-assessment
For each of these statements, decide on how well you agree. Give yourself five
if you agree very much and one if you do not agree at all.
•
I can recall the law of reflection.
•
I can d raw ray diagrams to show reflection.
•
The experiment on reflection helped my understanding.
Summary checklist
D I can understand and describe how light is reflected from a plane mirror
D I can recall the law of reflection
D I can draw ray diagrams to show reflection of light from a plane mirror.
0
..c
..c
C
C
E
0
191)
6 Light
>
> 6.2 Refraction
In this topic you will:
•
describe how light is refracted at the boundary between air
and glass or air and water
•
describe how light changes speed when it passes between
different substances
•
draw ray diagrams to show how light is refracted.
Getting started
Key words
Work in groups to discuss answers to these questions. be ready
to share your ideas w ith the rest of the class.
angle of refraction
1
2
List as many transparent materials as you can. Try to include
solids, liquids and gases.
Why do you think you cannot see clearly when looking
through a glass of water?
away from the
normal
bent
distorted
lenses
medium
refraction
towards the
normal
6.2 Refraction
Refraction
When you look through a glass of
water or through a wet window, you
cannot see clearly.
Look carefully at the picture, which
shows a glass of water on a table.
The background, through the glass
of water, appears distorted. Distorted
means changed to be less clear.
The background appears distorted
because of refraction.
The material that light passes through
is called a medium. Air, glass and water
are each examples of a medium for
light to pass through.
This glass of water is refracting the light passing through it.
You will remember that light travels very fast. The speed of light in air
is 300 000 kilometres per second. When light passes from air into water
or glass, the light travels more slowly. The table shows how the speed of
light changes according to the medium.
Medium
Speed of light in kilometres per second
air
300000
water
225000
glass
200000
The change of speed can cause the light to change direction.
Imagine you are on roller skates. You are moving at a constant speed
on a hard surface. The roller skate on one foot goes onto grass. What
happens? You will change direction because one roller skate is moving
slower than the other.
This is what happens when a ray of light passes from air into glass or
water. One side of the ray of light slows down first, causing it to change
direction.
Refraction of light is defined as the change in direction of light on
passing from one medium to another because of change in speed.
193 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Light passing from air into water or glass
This ray diagram shows what happens when light passes
from air into glass or water.
normal
The light slows down when it passes from air into glass
or water. This causes it to change direction.
The light passing from air into glass or water is bent
towards the normal. That means the refracted ray is
closer to the normal than it would be if the incident ray
just carried on in a straight line.
Notice also from the ray diagram that, when light passes
from air into glass or water, the angle of incidence is
greater than the angle of refraction. Both of these angles
are measured from the normal.
air
glass or water
+-' angle of incidence
angle of refraction
refracted ray
Light passing from air into glass o r water is bent
towards t he norma l.
Light passing from water or glass into air
The ray diagram in Figure 6.2.4 shows what happens
when a ray of light passes from water or glass into air.
refracted ray
normal
The light speeds up when it passes from glass or water
into air. This causes it to change direction.
We say that the light passing from glass or water into air
is bent away from the normal. That means the refracted
ray is further away from the normal than it would be if
the incident ray just carried on in a straight line.
You will also notice from the ray diagram that when
light passes from glass or water into air the angle of
refraction is greater than the angle of incidence. Both
of these angles are measured from the normal.
air
glass or water
incident ray
Light passing from glass or wat er into air is bent
away from the normal.
Refraction in everyday life
Refraction can be a nuisance. It can stop you
from seeing clearly through wet windows. Each
individual drop of water on the window refracts
light in a different direction, making it very difficult
to see. This is why many vehicles have windscreen
wipers. The windscreen wipers remove the water
drops. It is then easier to see clearly as au the
refraction from the glass is in the same direction.
Drops of water on g lass make it d ifficult to see because
of refraction.
194)
6.2 Refraction
Refraction can also be useful. Lenses are used in our eyes, in cameras
and in glasses that people wear, to cause refraction of light. A lens is a
curved piece of glass that is designed to refract ljght in a known way.
This phone has a lens to refract light for a photograph.
Different g lasses refract light in d iffere nt ways to help
people to see more clearly.
Questions
1
Complete the sentences, using 'faster' or slower.
a
Light travels ... in water than it does in air.
b Light travels ... in air than it does in glass.
2
Complete the sentence to describe refraction correctly.
Refraction of light happens when light ... direction because of a
change in ....
3
ray of light
This ray diagram shows a ray of light in air.
Copy and complete the ray diagram to show what happens
when the ray of light enters the glass.
Include on your diagram:
•
the normal
•
the angle of incidence
•
the refracted ray
•
the angle of refraction.
air
glass
4
This diagram shows a ray of light in water.
Copy and complete the ray diagram to show what
happens when the ray of light enters the air.
air
water
Include on your diagram:
•
the normal
•
the angle of incidence
•
the refracted ray
•
the angle of refraction.
ray of light
195 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Activity 6.2.1
Refraction effects
This activity shows three effects of refraction .
Effect 1: The appearing coin
Place a coin or small piece of metal at the bottom of an
opaque container, such as a cup.
Position yourself so that the coin is just out of view
behind the edge of the container as shown in the
diagram.
Now pour water into the cup until it is almost full.
Pour the water in carefully so the coin does not
move. The coin comes into view.
view from here
cup
coin
Can you use a ray diagram to explain why? You need to think about how a light ray travels
from the coin, up through the water and out into the air.
0
Effect 2: Broken pencil in water
Pour water into a transparent drinking glass until it is
about three-quarters full.
0
Set a pencil into the glass so it is resting at an angle.
View the glass and pencil from the side.
g lass
The pencil appears to be broken at the surface of the
water.
water
Can you use a ray diagram to explain why? You need to
think about how light trave ls from the pencil, through
the water and out through the side of the glass.
Effect 3: Broken pencil in water and oil
Repeat the demonstration in Effect 2: Broken pencil in water, but this time put water into
the glass until it is only half full. Now, gently pour cooking oil on top of the water until the
glass is about three-quarters full.
View the glass and the pencil from the side again.
How does the pencil appear this time?
What can you conclude about the speed of light in water and in cooking oi l?
196)
6.2 Refraction
Think like a scientist
Drawing accurate ray diagrams
In this investigation, you wil l make accurate ray diagrams from rays of light.
Work in groups of three or four.
You will need:
• ray box and power supply
• protractor
• glass block
• pencil
• plain paper
• ruler
• Make the room as dark as possible for this activity.
Method
1
Set up the equipment as shown in the diagram.
large sheet of
white paper
- + - - - - + - rectangular
glass block
pencil
'! !"-"' "9
.,.·
t/-
_;,_ -
'~~
"
1••
.
ray box
.
protractor
ruler
I: ; r : : : : ; 1 : ·r •: ·: •1 7 •11 ;• ~ ·r-::: ~ r•1 f •1 ~ ~ ~I
2
Use the pencil to draw around the glass block.
3
Switch on the ray box and position it so the light ray makes an angle with
the glass surface.
4
Use the pencil to mark the position of the incident ray in two places:
about 5 cm away from the glass b lock and where it meets the g lass block.
5
Do the same for the ray that emerges from the glass block on the other side.
6
Switch off the ray box and lift the glass block off the paper.
7
Use the ruler to join up the light rays.
8
Use the protractor to draw a normal at both surfaces.
9
Measure the angle of incidence and angle of reflection at both surfaces.
10 Repeat steps 2- 9, using different angles and a new piece of paper each time.
Make sure to include an angle of incidence of zero.
197 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Continued
Questions
1
What did you notice about the pairs of angles at each surface each time?
2
Plot a graph of your results for the first glass surface where the light ray
goes into the glass.
Put angle of incidence on the horizontal axis and angle of refraction on the
vertical axis.
Join your points with a line that passes through all of the points.
3
Describe the trend shown in the graph.
4
What do you observe when the angle of incidence is zero?
Self-assessment
Answer these questions about the group work.
•
What did you do in the group?
•
Did you make sure everyone in the group had a role?
•
Would you feel confident to lead a group activity next time?
Summary checklist
..C
D I can describe how light changes speed between air and either water or glass
D I ca n recall that a change in speed can make a light ray change direction
D I can recall which way light changes direction when it passes from air into glass or water
D I ca n recall which way light changes direction when it passes from glass or water into air.
E
0
198 )
6 .3 Making rainbows
> 6.3 Making rainbows
In this topic you will:
•
learn how white light is made from many colours
•
discover how dispersion of white light can be done with
a prism
•
be able to recall the colours of white light in the correct order.
Getting started
Work in groups to discuss the answer to these questions.
dispersion
•
Do you ever see a rainbow at night?
prism
•
Does the Sun have to be shining to enable you to see
a rainbow?
•
Does there have to be rain or recent rain to enable you
to see a rainbow?
•
What colours can you see in a rainbow?
spectrum
t riangular
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Newton's discovery
about light
The name Newton is often associated with forces, but
Isaac Newton made many other important discoveries.
In the year 1666, Newton showed that white light
could be split into different colours. The picture
shows Newton using light from the Sun, coming
through a hole. Newton is using a glass block in the
shape of a triangle to split the light into its colours.
He is shining the colours onto a screen.
The next picture shows what the colours look
like when seen on a screen.
The colours that make up white light
The spectrum
The range of colours that can be seen in white light is called a spectrum.
In the spectrum, the colours are not separate but they merge from one
to another.
Some people think Newton originally saw five or six colours, but most
people now agree that there are seven. In the order that they appear in
the spectrum, these seven colours are:
red
orange
yellow
green
blue
indigo
violet
You can remember the order of the colours using a made-up person's
name: 'ROY G. BIV'.
Dispersion
Dispersion means splitting light into different colours.
Dispersion happens because light is refracted. Each of
the different colours of light that make up white light
is refracted through a slightly different angle. This can
be shown by using a triangular prism. 'Triangular'
means in the shape of a triangle. A prism is a solid
shape such as the one that Newton used.
When a ray of white light passes through the prism,
the ray is refracted. Violet light is refracted through
the largest angle and red light is refracted through
the smallest angle. You can see this in the picture.
200)
Dispersion of white light, using a t riangular prism
6 .3 Making rainbows
Rainbows
A rainbow is formed when drops of water in the air
cause dispersion of light. The light is also reflected
from inside the drops of water. That means that, for
you to see a rainbow:
•
the Sun must be shining, to provide bright light
•
there must be rain or small drops of water
in the air, to cause dispersion of light
•
the Sun must be behind you, because the water
drops reflect the light inside them.
The drops of water from the hosepipe in Figure 6.3.4 are making
a rainbow. The Sun is shining and the Sun is behind the camera.
Drops of water on a sunny day can cause a rainbow.
Questions
1
What name is given to white light being split into different colours?
refraction
2
dispersion
reflection
conduction
T he diagram shows a glass block being used to separate white light.
What name describes this piece of equipment?
Write one letter.
A
round glass cylinder
B
square glass prism
C
triangular glass prism
D
hexagonal glass prism
201 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
The diagram shows white light being
separated into different colours. The colours
are seen on a white screen.
3
a
Which letter shows the position of red
light on the screen?
glass prism
b Which letter shows the colour of light that is
refracted through the smallest angle?
What word describes the range of colours seen on the screen?
c
refraction
reflected
separated
screen
spectrum
4
Explain why drops of water are needed for a rainbow to be seen.
5
When looking at a rainbow, some people see indigo and violet as the
same colour.
How many colours will these people say they can see in the rainbow?
:.....
Think like a scientist
()
Making a rainbow
In this activity, you will change variables and describe how observations change.
Work in groups of two or three.
You will need:
• a ray box and suitable power supply • a triangular glass prism
• a piece of white paper or card to use as a screen
Safety
Do not put your eye closer to the prism
than about
metre. The light will
become very bright and could cause
damage to your eye.
\, \.
incident ray
glass prism
Make the room as dark as possible for
this activity.
Set up the equipment as shown in the
diagram.
Method: Part 1
1
Adjust the positions of the ray box and the screen until you see the colours
of the rainbow on the screen.
2
Move the screen closer to the prism.
3
Move the screen further away from the screen.
202)
screen
6 .3 Making rainbows
Continued
Questions
1
2
a
How many colours can you see on the screen?
b
List the colours in order starting from red.
Name the co lour that is refracted :
a
through the smallest angle
b through the largest angle.
3
Describe two th ings that happened to the colours when:
a
the screen was moved closer to the prism
b
the screen was moved further away from the prism.
Method: Part 2
1
Remove the screen and stand about 1 metre from the prism, in the same
direction as the screen had been.
2
Move so that you are looking into the refracted rays with one eye.
You may find it easier to cover the other eye.
3
Move from side to side so that you can see the different colours.
4
Increase the distance between your eye and the prism to about 2 metres.
5
Again, move from side to side so that you can see the different co lours.
Questions
1
Describe two differences in the observations when you moved further away.
2
Describe one advantage and one disadvantage of Method: Part 1 and
Method: Part 2 for observing the colours.
3
This activity is an analogy for how rainbows form. Describe one strength
and one limitation of this analogy.
Self-assessment
Different people see different numbers of co lours in this activity.
The numbers of colours usually vary from 5 to 7.
Did you see the same number as everyone else in the class?
Suggest reasons why people see different numbers of colours.
Summary checklist
D I can recal l that white light is made from different colours of light
D I can describe how to use a prism to produce dispersion of white light
D I can list the seven colours in order starting from red.
-
0
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
> 6.4 Colours of light
In this topic you will:
•
discover what happens when colours of light are added
•
discover what happens when colours of light are subtracted
•
discover why we see different colours.
Getting started
Key words
Work in pairs.
absorbed
Make a list of all the colours you can see in this picture of flowers.
coloured filters
cyan
How many did you get? How does this number compare with
other groups?
magenta
non.luminous
primary colours
subtraction
transmit
6.4 Colours of light
Primary colours
Topic 3.3 explained that there are seven colours in white light. These are
the colours that can be seen in the rainbow.
However, there are three colours of light from which all other colours
of light can be made. These are called the primary colours. The primary
colours cannot be made by mixjng any other colours of light.
The primary colours of light are:
•
red
•
green
•
blue.
The primary colours of light are different from the p rimary colours in
paints. The colours in light mix differently from the colours in paint.
Adding colours of light
The diagram shows what happens when three beams of light, each
of a different primary colour, overlap.
You can see the effect of adding the primary colours:
•
red + green = yellow
red + blue = magenta
blue + green = cyan
•
red + green + blue = white.
The different colours that you see on a mobile phone, computer or
television are all produced from combinations of the three primary
colours of light.
Colours formed by overlapp ing the
t hree primary colours of light
When you look very closely at some types of computer monitor,
television or phone screen, you can see the individual sources of red,
green and blue light.
The colours on t his p hone d isplay are made by adding the
three p rimary colours of light.
Close-up of a television screen showing t he sources of the
primary colours of lig ht.
205)
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
When you look at a television or phone screen, you see far more colours
than just red, green, blue, cyan, magenta, yellow and white. Most screens
can display 256 different colours. Changing the brightness of the primary
colours makes all these different colours. For example, orange is made by
adding red and green, but with the red brighter than the green. Research
has shown that 256 is the maximum number of colours that most people
can see.
Subtracting colours of light
You have probably used a filter in your chemistry lessons. Filters
are used to remove something from a mixture.
You can also use coloured filters to remove colours from light.
If a transparent piece of coloured glass or plastic is placed in
front of a white light, then only light of that colour will be
transmitted (get through). All the other colours will be absorbed.
A common example of coloured filters is in trafiic lights.
The trafiic lights use three identical white lamps. In front of each
lamp is a coloured filter for red, yellow or green.
Take the red filter as the example to see how this works.
White light, from the lamp, is made from the seven colours of
light: red, orange, yellow, green, blue, indigo and violet.
When these seven colours arrive at the red filter, only red is
transmitted. The other six are absorbed. This is shown in
the diagram.
These traffic lights use coloured filters.
Figure 6.4.3: A coloured filter works by absorbing t he colours of light t hat are different from
the colour of the filter.
This is an example of subtraction of light. White light has had six
colours subtracted to leave only red.
In the traffic lights, the yellow and green filters work in exactly the same
way. Each of them absorbs six colours and only transmits one colour.
206)
6.4 Colours of light
The blue stage light in the picture has a white lamp and a blue filter. If you
look carefully, you can see where the white lamp is inside the black case.
The colours of the fi lters in stage lights can be changed to produce
different colours.
Photographers sometimes use coloured filters on a camera to get
different effects.
This stage light is using a white lamp and a b lue filter.
What colour was the fi lter used in taking t his phot ograph?
As with numbers, it is possible to subtract colours of light until the end
result is zero.
For example, if white light shines on a green filter, only green light will
get through. The other colours of the white light are absorbed.
If this green light then shines on a red filter then no light will get
through. Green is one of the colours that a red filter absorbs.
white light
only green
light passes
through
green filter
no green light
passes through
red filter
The result of using two different coloured filters
207 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Seeing colours
When you look at a non-luminous object, you see the light that is
reflected from the object. 'Non-luminous' means the object does not
emit its own light.
Look at the flower in the picture.
The flower is seen in white light. The flower looks yellow because it
reflects only yellow light. The flower absorbs the other six colours in
white light. This is shown in the diagram.
white light coming in
yellow light
yellow surface
The flower appears yellow because it reflects yellow light and absorbs t he other colours.
A white object reflects all the colours in white light equally.
A black object absorbs all the colours in white light and does not
reflect any.
These three balls appear black, red or white, according which colours
of light they reflect and which they absorb.
208)
6.4 Colours of light
Look at the two cubes in Figure 6.4.7. One is red and
the other is blue. The cubes are shown in different
colours of light.
The red cube appears black when seen in green light.
This is because red objects only reflect red light.
They absorb all other colours. Here, the red cube is
absorbing the blue light and not reflecting any light.
The blue cube appears black when seen in red light for
the same reason. It absorbs the red light and does not
reflect any light.
A
blue and red
cubes seen
in white light
B
blue and red
cubes seen
in blue light
C
blue and red
cubes seen
in red light
Questio ns
1
List the three primary colours of light.
2
Name the colour produced when
3
a blue and red cubes in white light; b the same cubes
in green light; c t he same cubes in red light.
a
red light and blue light are added together
b
red light and green light are added together
c
red, green and blue lights are added together.
A stage light uses a white lamp.
What colour of light will be seen when:
a
a yellow filter is used
b an orange filter is used.
4
a
A green ball appears green. What colour of light could be
shining on the green ball? Choose two.
b lue
green
red
white
magenta
b A blue ball appears black. What two colours of light could be
shining on the blue ball?
b lue
5
green
red
white
A T-shirt looks red. What could explain this?
Write three letters.
A
the T-shirt is red and is seen in white light
B the T-shirt is red and is seen in red light
C
the T-shirt is blue and is seen in green light
D the T-shirt is white and is seen in red light
E
the T-shirt is yellow and is seen in blue light
209)
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Activity 6.4.1
Making colours on the screen
Many computer applications, such as those for word-processing
and slide-making, have colour options. In the 'more colours'
options of these there are RGB tools to customise co lours.
The letters RGB stand for 'red', 'green' and 'blue', the primary
colours of light. You can adjust these to make whatever colour
you want. For example, bright red has:
•
R at maximum
•
G at zero
•
Bat zero.
Bright yellow has:
•
R at maximum
•
G at maximum
•
Bat zero.
Try making:
•
•
•
•
magenta
cyan
white
black.
Now make some other colours of your choice.
In each case, write down the RGB settings for each colour.
Think like a scientist
:;::;
Identify the colour
In this investigation, you wi ll make predictions about colours and light.
Work in groups of two or three.
You will need:
• white paper and coloured paper
• a room that can be darkened
210)
• coloured p ens
• flashlights
• coloured filters
6.4 Colours of light
Continued
Method
1
Write the names of some colours on a piece of coloured paper.
Use different coloured pens to write each word. The colours do not
have to match correctly.
For example, on yellow paper, write:
•
'blue' with b lue pen
•
'red' with green pen
•
'green' with blue pen.
2
Use the flashlight and a red fi lter to illuminate the paper.
3
Ask someone from a different group to identify:
4
•
the colour of the paper
•
the words that are written in the correct co lours
•
the colours of pen used to write the other words.
Vary the words, the colours of the pens, the colours of the paper and the
colours of the filters, and repeat steps 1-3.
Questions
1
Which colour combinations were easiest to get correct?
2
Which colour combinations were most difficult to get correct?
Self-assessment
1
What parts of this topic are easiest to understand?
2
What parts of th is topic are most difficult to understand?
3
What part of this topic could you teach to someone else?
Summary checklist
U
D I can recall the three primary colours of light
D I can recall the colours that are made when these primary colours are added together
D I can understand that filters work by subtracting light
D I can predict what will happen when light of different colours shines on filters of different
colours
D I can understand why coloured objects appear coloured when seen in white light
0 I can predict the colours that objects will appear to be, when seen in light of different colours.
211)
>
6 Light
> 6.5 Galaxies
In t his topic you wil l:
•
discover that galaxies contain dust, gas, stars and other solar
systems.
Getting started
Work in pairs.
Arrange these objects in order from sma ll est to largest.
star
solar system
planet
galaxy
moon
elliptical
galaxy
irregular
spiral
stellar dust
6.5 Galaxies
The Milky Way
If you look at the sky on a clear night, far away from any lights, you can
see a milky band across the sky. This milky band is part of the galaxy
where we live, called the Milky Way. The photograph shows what this
looks like through a camera set for very low light conditions.
This is part of our own g alaxy, t he Milky Way.
The word 'galaxy' comes from a Greek word for 'milky' .
Shapes of galaxies
The reason why our own galaxy looks like a
band across the sky is because of the shape
of the galaxy. The Milky Way is a SJJiral
galaxy. If you were to look at the Milky Way
from far away, it would appear as a spiral.
Because we live in a spiral galaxy, we can
only see one 'arm' of the spiral, which is
that band across the sky. In fact, most of
the stars we see at night are in our own
galaxy. There are an estimated 250000000
stars in the Milky Way including our Sun.
This is what the M ilky Way wo uld look like fro m far away.
There are other galaxies in the universe besides our own. The word
'universe' is used to describe all of space and everything in it.
These other galaxies have different shapes, and they are classified
according to shape. They are called elliptical galaxies or irregular galaxies.
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
The three different shapes of galaxy a: Spiral, b: Elliptical, c: Irregular
The closest known galaxy to the Milky Way is called the Canis Major
Dwarf Galaxy. It is elliptical in shape and a distance of away from us.
What are galaxies made of?
Galaxies are made from stellar dust, gas, stars and solar systems held
together by gravity. Stellar dust is the dust that is found in space. The
Earth is travelling through a cloud of stellar dust that is estimated to
contain an average of one dust particle in every million cubic metres
of space!
The gravity holding a galaxy together is very strong because galaxies
are very large and have very large mass. Even if you could travel at the
speed of light (300000 kilometres per second), it would take you more
than 100 000 years to cross from one side of the Milky Way to the other!
Scientists estimate the mass of the Milky Way to be 1500000000000 times
the mass of the Sun.
How many galaxies are there?
Scientists have counted the galaxies in one part of space. The scientists
then multiplied this number up to estimate the number of galaxies in the
universe. The answer they got was l 00 000 000 000 galaxies!
Estimates such as this may not be accurate. There could actually be
more or fewer galaxies in the part of space that the scientists counted
compared with the rest of the universe. A lso, the scientists may not
know the total volume of the universe accurately.
214 )
6.5 Galaxies
Questions
1
List the three different shapes of galaxies.
2
Which of these are found in galaxies?
Choose all that are correct from the list.
planet
star
universe
stellar gas
3
Name the force that holds the parts of a galaxy together.
4
Explain why most of the stars we see in the night sky are from our
own galaxy and not from other galaxies.
5
Suggest why scientists can only estimate the number of stars in the
Milky Way and not know the number accurately.
Think like a scientist
Estimating large numbers
In th is investigation, you will use an analogy for estimating the number of
stars in a galaxy.
Work in groups of two or three.
You will need:
• one large cup or other container filled with coarse sand or fine gravel, for the
whole class
• a hand lens (magnifying g lass) for each group
• a piece of white paper for each group
• small container for the whole class
• access to laboratory equipment for measuring masses and volumes
• a calculator for each group
Scientists cannot count the number of stars in a galaxy because there are too
many. However, scientists can estimate the number of stars in a galaxy.
You are going to estimate the number of grains of sand in your container.
There are too many to count them all, so this activity is an analogy for how
scientists estimate numbers of stars.
Method
1
Put a small quantity of sand from the large container onto the white paper and
separate the grains. You should only put out the quantity you can count easily.
Continued
215 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Continued
2
Count the grains, record the number, and put the grains into the small container.
3
Do the same again: count some grains from the large container and then add
them to the small container.
4
Write down the total number of grains your group put in the small container.
5
Now decide as a class whether you want to work in mass or in volume for the
last two steps.
6
Measure the total mass or volume of the grains in the small container.
7
Now put these back into the large container and measure the tota l mass or
volume of sand in that.
Questions
1
What was the tota l number of grains the class put in the small container?
Ca ll this value G for grains.
2
What was the tota l vo lume or mass of the grains in the small container?
Call this value S for small.
3
What was the tota l volume or mass of the grains in the large container?
Call this value L for large.
4
Calculate the va lue of G x
5
This number is an estimate of the tota l number of grains in the large container.
a
t
Explain the advantage of this method compared to counting all the grains
in the large container.
b Give reasons why the estimate may not be accurate.
c
Suggest some ways that the estimate could be made more accurate.
6
Suggest how working as a whole class is an analogy for how scientists studying
the Milky Way work.
7
Knowing roughly how long it took you to count your grains in step 2, estimate
how long it wou ld take you to count all the grains in the large container.
8
Suggest how you could estimate the number of grains of sand on a beach.
Self-assessment
Decide how confident you are about each of these:
•
understanding how this method of estimating works
•
whether you cou ld apply this method to estimating some other large quant ity.
2 16 )
6.5 Galaxies
Summary checklist
D I can understand what galaxies are
0 I can recall the three shapes of galaxies
D I can recall that galaxies contain stellar dust and gas, stars and solar systems
D I can understand that gravity holds all t he parts of a galaxy together in space.
0
0
..c
..c
C
C
E
0
217 )
6 Light
>
> 6.6 Rocks in space
In this topic you will:
•
discover that asteroids are rocks that are smaller than planets
•
know that scientists believe asteroids to be rocks left over
from the formation of the Solar System
Getting started
Work in groups.
Make a list of different types of objects in the Solar System.
asteroid belt
asteroids
craters
impacts
6.6 Rocks in space
Asteroids
Asteroids are objects made from rock that orbits the Sun.
Asteroids range in size up to 975 km across. The smallest asteroid that
has been studied is 2 m across.
Most asteroids are not regular shapes, just as rocks on Earth are not
regular shapes.
Scientists describe the shape of most asteroids as being similar to the
shape of potatoes.
Most of the asteroids in the Solar System orbit the Sun between the
orbits of Mars and Jupiter. This part of the Solar System is called the
asteroid belt.
There are millions of asteroids. Some that have been studied have been
given names.
The largest asteroid is called Ceres and was discovered in the year 1801.
When Ceres was discovered, scientists thought it was a new planet. As
Ceres looked much smaller than a planet, the term asteroid was introduced.
This photograph of Ceres, was taken by a spacecraft in 2015.
Ceres looks like a small planet. It is round, with a diameter of 975 km,
and covered with craters.
Ceres also has a core, a mantle and a crust like some planets.
Scientists think that Ceres would have become a planet if it had
continued to grow during the formation of the Solar System.
The next photograph shows asteroid Itokawa, which is one of the
smallest asteroids to be visited by a spacecraft.
Asteroid Itokawa is about 530m long and about 250m wide. In the
year 2005, a spacecraft collected samples from the surface of Itokawa. Ceres is an unusual asteroid c;i.nd
It was the smallest asteroid to be visited at that time.
also the largest.
Study of the samples has given scientists more evidence about how the
Solar System formed.
ltokawa appears to be made from lumps of rock. These lumps of rock
appear to have come from other small planets or moons which have
been broken by impacts. The force of gravity holding the lumps of rock
together is weak because the asteroid is a relatively small object. When
an asteroid such as Itokawa passes a large object such as a planet, tidal
forces can change the shape of the asteroid.
Some asteroids are made from a single piece of rock. Scientists know
this because these asteroids are small and spin quickly. The force of
ltokawa is an asteroid t hat has
gravity in these asteroids would be too weak to hold separate pieces
been st udied by spacecraft.
of rock together.
219 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
.. .. ••
. . ... ... .......
Asteroids and Earth
,
Scientists think that a large asteroid impacts
the Earth on average every 130 000 years.
Smaller asteroids impact with Earth
very frequently.
The map in Figure 6.6.3 shows where
asteroids impacted Earth between the
years 1994-2013. These smaller asteroids
were less than diameter and broke apart
in the atmosphere, so never reached the
Earth's surface.
"'.
...:..
..
.,.
.
·i.
...
..... .. ... .... . ,, .:
:·: . . .. -.
. ... ....
....
. ...
.
. ...
•
••• :
I
The map shows the positions of asteroid impacts on Earth
between 1994 and 2013.
There are two reasons why asteroids impact
with Earth.
•
1he Earth exerts a strong force of gravity on passing objects such
as asteroids.
•
Many asteroids have orbits that pass relatively close to Earth.
Questions
1
Describe what is meant by the term 'asteroid'.
2
Some asteroids have diameters between and .
Explain why these asteroids are classed as small objects in the
Solar System.
3
The asteroid Ceres is covered with craters. Suggest how these
craters were formed.
4
Describe where the rocks came from to form asteroids.
Activity 6.6.1
:;:::::;
Making a model asteroid
In this activity, you will make a model of an asteroid.
You will need:
• a selection of small rocks
• black acrylic paint
• paint brushes
220)
• some coarse sand
• white acrylic paint
• glue suitable for stone
• trays for mixing paint
""
6.6 Rocks in space
Continued
Method
5
Use an internet search engine or the pictures in this topic to plan what your model will
look like.
6
Choose a small rock and, if necessary, attach sand onto the surface with glue to give a
rough texture.
7
When the g lue has dried, you can paint your asteroid.
8
Mix the black and white paints to achieve the colours of grey that you want.
9
Together with the other models in your class, you could make a model of part of the
asteroid belt.
Questions
1
Asteroids are d ifferent from planets. Describe one way that your model shows this
difference.
2
Some large asteroids that your model could represent have a diameter of 200 km.
The planet Jupiter has a diameter of . Calculate how many times larger Jupiter
is than these asteroids.
3
a
Use a ruler to measure the length of your model asteroid.
b Use your answer to question 2 to calculate the size of model you wou ld need
to make for the planet Jupiter on the same scale.
C
Think like a scientist
What happened at Tunguska?
In this investigation, you will look at evidence that supports or contradicts hypotheses.
Work in groups of two or three.
Method
1
Read these facts.
•
Tunguska is in northern Russia, far from any towns or cities.
There is forest there, with many trees.
•
In the morning of 30 June 1908 there was a very large explosion at Tunguska,
between 5 km and 10 km above the ground.
•
People living over 800 km away could see and hear the explosion.
•
Vibrations from the explosion were recorded almost 5000km away.
•
The explosion flattened trees over an area of 2000 km 2 •
Continued
221 )
_ _ _ _ _6_L_ig_h_t_ _ _ _ _ _ _ _ _ _ _ __,)
Continued
2
3
Read these five hypotheses of what caused the explosion.
1
A comet impacting the Earth.
2
A type of volcano erupting.
3
Testing of a new type of bomb.
4
An alien spacecraft crashing.
5
An asteroid impacting the Earth.
Consider the evidence.
•
All the trees that fell are pointing outwards from a central position.
•
People discovered how to make very powerful bombs in 1945.
•
No bomb this powerful has ever been made.
•
Tunguska is very far from tectonic plate boundaries.
•
Most comets break up higher than
•
A small part of a comet is made from rock.
•
Small rocky fragments have been found that show the signs of fa lling
through the atmosphere at very high speed.
•
No metal parts have been found at Tunguska.
in the atmosphere.
Questions
1
Use the evidence to decide whether each of the five hypotheses can
be supported or contradicted.
You can also use facts given in this topic as evidence.
Write about each hypothesis in turn.
2
Decide, using this evidence:
a
which of the hypotheses are most likely
b which of the hypotheses are most unlikely.
3
Explain some of the limitations of the conclusions you have made.
Peer-assessment
Find another group whose answers to question 2 are different from yours.
1
Are you convinced by their conclusions?
2
If not, can you understand why they made these conclusions?
222)
6.6 Rocks in space
Summary checklist
D I can describe what is meant by the term asteroid
0 I can recall where most asteroids in the Solar System are found
D I can know that asteroids are formed from rocks left over from the formation of the
Solar System
D I can know that some asteroids pass close by Earth and can, from time to time,
impact Earth.
0
0
..c
..c
C
C
E
0
223)
_ _ _ _ _6_ L_ig
_h_t_ _ _ _ _ _ _ _ _ _ _ _ _)
Check your progress
6 .1 A plane mirror is a type of mirror.
Which of these words describes the meaning of plane?
flat
irregular
round
[1]
smooth
6 .2 Copy and complete the sentence that describes how light is reflected
from a plane mirror.
The angle of reflection is ... to the angle of ... .
[2]
6.3 Copy and complete the diagram to show how light is reflected from the
plane mirror.
You do not have to measure angles.
Label the reflected ray and the angles of incidence and reflection.
normal
plane mirror
6 .4 The motorcycle in the picture is fitted with mirrors.
The motorcycle rider can see objects that are behind the motorcycle
by using these mirrors.
[3]
Draw a ray diagram to show how the rider can see a ray of light that is
coming from behind.
[4]
6 .5 State the name given to light changing direction when the light passes
from air into water.
[1]
6.6 Copy and complete each of these sentences with either the words 'speeds up'
or the words 'slows down'.
a
When light passes from air into glass, the light ... .
b
When light passes from air into water, the light ... .
C
When light passes from glass into air, the light . ...
[1]
6 .7 Copy these sentences.
[2]
Write T or F after each one to show if it is true or false.
In a ray diagram, the angle of incidence is measured between the light ray
and the surface.
In a ray diagram, the angle of refraction is measured between the light ray
and the normal.
In a ray diagram, the normal is a line at 90° to the surface.
6.8 Copy these ray diagrams to show what happens to the light rays.
On each diagram, draw and label:
•
the normal
•
the refracted ray
•
the angles of incidence and refraction.
•
You do not have to measure any angles.
[4]
a
b
air
water
air
glass
6 Light
6.9 Complete the sentences by using words from the list.
Copy and complete word can be used once, more than once or not at all.
dispersion
prism
colours
orange
violet
blue
[5]
spectrum
reflection
White light can be split into its component ... .
This is called .. . and can be done with a ... .
The range of colours is called a ....
The range starts with red and ends with ....
6.10 D escribe the light that will emerge at points A, Band C when white light
shines on each of these filters.
•
If coloured light will emerge, write the colour.
•
If white light will emerge, write 'no change'.
•
If no light will emerge, write 'no light'.
a
[1]
white light
►
A
red fi lter
[1]
b
white light
►
C
blue filter
C
white light
►1
red filter
[1]
B
green filter
6 .11 A theatre uses coloured lights to make objects appear different.
Write the colour that each of these objects will appear.
a
A red book in white light.
[1]
b
A green door in green light.
[1]
c
A white T-shirt in blue light.
[1]
d
A blue ball in green light.
[1]
6 .12 Two different coloured lights of the same brightness shine onto a white wall.
T he two colours of light overlap.
Write the colours that will be seen at the points X, Y and Z.
a
whitewall
b
white wall
C
white wall
d
State the colour that would be seen if red, green and blue lights
of the same brightness all overlapped on the white wall.
[1]
_ _ _ _ _6_ L_ig
_h_t_ _ _ _ _ _ _ _ _ _ _ _ _)
6.13 a
List the four things that make up a galaxy.
[2]
b
Name the galaxy that contains the Earth.
[1]
6.14 Asteroids are different from planets. State two features of asteroids
that make them different from planets.
[2]
Project
Project: Investigating refraction
Refraction is all around you every day. Refraction is generally what allows you see
transparent objects.
Dissolve some white sugar or salt in water. Make sure it is all dissolved so you have
a transparent solution.
Now take a transparent container holding some water. Look at the water from the
side and slowly pour your sugar or salt solution into the water.
Describe what you see.
How can you see both liquids if they are both transparent?
Your task
You will do experiments that will help you explain what you see when you pour the
sugar or salt solution into water.
Work in groups.
You can use equipment such as:
•
a ray box and power supply
•
glass or plastic containers with smooth, flat sides
•
water
•
other transparent liquids
•
sugar and salt to dissolve in water.
Safety
Remember to keep liquids away from the power supply and the ray box.
Carry out experiments using the method in Think like a scientist: Drawing accurate ray
diagrams in Topic 6.2.
Investigate how each substance refracts light.
When you dissolve sugar or salt in water, does it change how the light is refracted?
Does the concentration of the sugar or salt affect the refraction?
Which substance refracts the light through the largest angle?
Which substance refracts the light through the smallest angle?
Record all your results and present them in the most effective way.
Can you now explain what you see when you pour the sugar or salt solution into water?
229)
Diet and growth
> 7.1 Nutrients
In this topic you will:
•
learn about the six types of nutrient that everyone needs
to eat
•
find out why they need these nutrients
•
learn about some good sources of these nutrients.
.
- -
, -
Key wor~s
anaemia
Everyone needs energy to stay alive and to do things.
They get their energy from the food that they eat.
carbohydrate
Think about the answers to these two questions on your own.
fat
Then turn to your partner and discuss your ideas about
each question.
Be ready to share your ideas with the rest of the class.
•
Which kinds of food are best for giving you energy?
•
What happens to your food after you have swallowed it,
before it gives you energy?
minerals
nutrients
oil
protein
starch
vitamin A
vitamin C
vitamin D
vitamins
230)
V
t "I
7 .1 Nutrients
Carbohydrates, fats and proteins
The photograph shows a plate of food .
There are several different kinds of food on the plate. How does each of
these foods help the body to stay healthy, and to have energy?
The rice contains a lot of starch. Starch is a type of carbohydrate.
After you have eaten starch, the body breaks it down to make a sugar
called glucose. You may remember that glucose is the fuel that your
cells use for respiration, to release energy. So starch, sugar and other
carbohydrates are needed to give you energy.
The chicken and beans
contain a lot of protein.
Protein is important
for making new cells in
the body. So you need
protein to help the body
to grow, or to repair
itself if it gets damaged.
Protein is also needed to
make haemoglobin and
antibodies.
The avocado contains
fats and oils. Fats and
oils are very simi lar, but
fats are solid at normal
temperatures and oils
are liquid. Fats and oils
give you energy. They are
also needed to make cell
membranes
231 )
______1__
o_ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Protein, carbohydrate and fat are nutrients. Nutrients are substances
found in food, that you need to stay healthy. These three photographs
some of the kinds of food that you can eat to get these nutrients.
These foods are good sources of p rote in. These foods are good sources of starch
(a type of carbohydrate
These foods contain a lot of fat.
Energy stores
You do not eat alJ the time, but you need energy alJ the time. You get
almost all of your energy from the carbohydrates and fats that you eat.
You can also get energy from protein if you run out of carbohydrates
and fats.
You store a little bit of carbohydrate, and quite a lot
of fat, in your body. These energy stores provide you
with energy whenever you need it.
You store a small amount of carbohydrate in your
cells, especially in the liver and muscles. These are
short-term energy stores.
For long-term stores, your body stores fat in special
cells under-neath the skin and around some of the
body organs.
Fat stores in the body also provide heat insulation.
Animals that live in cold places, like this seal, have
a lot of fat stores underneath their skin, to help to
stop them losing heat from their body.
232)
--
7 .1 Nutrients
Act ivity 7 .1.1
Protein and carbohydrate in food
Work with a partner for this activity.
Think about what both of you have eaten so far today. Make a list.
Which foods do you think contain a lot of protein?
In your list, draw a green circle around each one.
Which foods do you think contain a lot of carbohydrate?
In your list, draw a blue circle around each one.
Use the internet or a reference book to see if you are right.
Make changes to your list and circles if you were not correct.
r
Think like a scientist
Testing foods for starch
You are going to try to find out which types of food contain starch.
You can use iodine solution to find out if a food contains starch.
Iodine solution is orange-brown. When it mixes with starch, it becomes very dark blue-black.
You will need:
•
at least six different kinds of food
•
some paper plates or other place to put the pieces of food, keeping them separate
•
a white tile
•
a bottle of iodine solution, with a dropper
Method
1
Collect six different kinds of food. Try to include some foods that come from plants,
and some that come from animals. Make sure you keep them completely separate
from one another.
2
Draw a results table like this:
Food
Colour of iodine solution
after adding to the food
- - - - - - - - - - - - - - - - - - - - - - - - -
Does the food
contain starch?
- - - - - - - - Continued
233)
______1__
o_ie_t_a_n_d_g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Continued
Method
3
Take a small piece of the first food. Put it onto a white tile.
4
Add a few drops of iodine solution. Record the colour that you see in your results table.
5
C lean the white ti le. Now repeat steps 2 and 3 for the other foods, making sure to
clean the tile each time.
6
Complete the last column in your results table.
Questions
1
Explain why it was important to keep all the foods separate from one another.
2
Suggest why it is a good idea to use a white tile for this experiment.
3
In your resu lts table, which column shows your results?
Which column shows your conclusions?
4
Did any of the foods that came from plants contain starch?
5
Did any of the foods that came from animals contain starch?
Questions
1
Copy and complete this table.
Nutrient
Examples of foods that
contain a lot of this nutrient
Why the body needs this nutrient
Protein
Carbohydrate
Fat
2
Explain the difference between the meanings of the words 'food'
and ' nutrient'.
234)
7 .1 Nutrients
Vitamins
Vitamins are nutrients that are needed in only small amounts, but if you
don't eat them you can get ill.
There are lots of different kinds of vitamin. Each kind is given a letter.
Vitamin A
Vitamin A is needed to help your eyes to work well, so
that your vision is good. It is particularly important for
helping us to see when it is quite dark. People who don't
have enough vitamin A in their diet may not be able to
see anything at night. It also helps your white blood cells
to fight pathogens.
You get vitamin A by eating green vegetables, carrots and
squash (such as pumpkin), fruit, foods made from milk
(such as cheese) and some kinds of fish .
Vitamin C
Vitamin C helps the skin to stay strong and to heal quickly
if it is damaged. It keeps blood vessels and bones healthy.
People who don't eat enough vitamin C can get an illness
cal led scurvy. A person with scurvy feels weak and may
have swollen, bleeding gums.
You get vitamin C by eating fresh fruit and vegetables.
Citrus fruits are particularly rich in vitamin C. Potatoes and
colourful berries are also good sources of vitamin C.
In the past, before anyone knew about vitamin C, sailors
on long sea voyages often got scurvy. This was because
they had no fresh fruit or vegetables to eat.
Vitamin D
Vitamin D is needed for strong bones and teeth. It helps
the body to absorb calcium from the food that you eat.
There are not many kinds of food that contain vitamin D.
Oily fish is probably the best source. But for most people,
most vitamin D does not come from the food that you
eat. Instead, vitamin Dis made in the skin when sunlight
falls onto it.
People who never go outdoors, or who never get any
sun on their skin, may not get enough vitamin D. This is
most likely to happen if you live in a country far from the
equator, or where there is not much sunshine.
In children, lack of vitamin D can stop their bones growing
normally. This illness is called rickets.
235 )
______1__
o_ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Activity 7 .1.1
Vitamins poster
Work in a group of three for this activity.
You will need a big piece of paper, and some coloured pens or pencils.
Divide the sheet of paper into three equa l areas. Label the areas Vitamin A,
Vitamin C and Vitamin D.
Use the information in this book, the internet and/or the library to find out which
foods contain a lot of each vitamin.
Draw pictures of the foods in each space. If you like, you could also cut out
some pictures of foods from packaging or magazines, and stick the pictures
onto your poster.
Minerals
There are several different kinds of mineral that you need to eat.
Two of the most important ones are calcium and iron.
Calcium
Bones and teeth contain calcium, so you need to eat plenty
of calcium to make them strong. Foods made from milk
are excellent sources of calcium. Seeds and some types of
nut (for example, almonds) also contain
a lot of calcium.
Iron
Iron is needed to make haemoglobin. If you don't eat
enough iron, you don't make enough haemoglobin, so
not enough oxygen is transported around the body. This
causes an illness called anaemia, which makes a person feel
very tired. Good sources of iron include meat (especially
red meat), dark green vegetables, many kinds of fish and
shellfish and some nuts and seeds.
236)
7 .1 Nutrients
Questions
3
Look back at question 1. Draw a similar
table, but include vitamin A, vitamin C,
vitamin D , calcium and iron instead of
protein, carbohydrate and fats.
Then complete your table.
4
Use your knowledge about respiration to
explain why a person with anaemia does
not have much energy.
5
These bell peppers are stuffed with beef
mince and vegetables, and topped with
cheese. They contain a lot of iron
and calcium.
What other nutrients do you think this
meal contains? Explain your answer.
Water
There is one more nutrient to add to the list of what you need to take
into your body each day. This is water.
Water is needed for many different purposes in the body. Cells and
blood contain a lot of water. Almost 90% of a person's body weight
is made up of water. Water in cells allows all the different chemicals
inside them to dissolve, so that they can react together. These reactions
keep us alive. Water in blood allows it to flow easily, transporting
substances all over the body.
Summary checklist
D I can list the six types of nutrient that I
need in my diet.
D I can explain why I need each of these
nutrients.
D I can list some foods that contain each
of these nutrients.
______1__
o_ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
> 7.2 A balanced diet
In this topic you will:
•
find out what is meant by a ba lanced diet
•
think about the nutrients you should try to eat each day
•
learn why you should try not to eat too much of some nutrients.
Getting started
Key words
Try to answer these questions on your own.
balanced diet
•
Can you name the six nutrients that you need to eat?
•
Which three nutrients can give you energy?
•
Which two groups of nutrients are needed in only sma ll amounts?
constipation
fibre
7 .2 A balanced diet
Diet
Your diet is the food that you eat each day. Your diet should provide you
with some of all the different kinds of nutrients. It should also give you
the right amount of energy.
A diet that provides all the different kinds of nutrients, and the right
amount of energy, is called a balanced diet.
How much energy?
Each day, the energy in the food you eat should be approximately equal
to the energy that you use up. Most of your energy comes from the
carbohydrates and fat that you eat.
Different people use different amounts of energy. For example:
•
•
•
•
•
If you do a Jot of sport, or walk or run a Jot each day, you use
more energy.
If you don't move around much, you use less energy.
Some people's genes mean that their body uses up energy more
quickly than other people doing the same thing.
If you are growing fast, you need extra energy to help your cells
to divide.
Tall people use more energy to move their body around than
small people.
The bar chart shows some examples of the energy that different people
need each day. A megajoule is one million joules.
12 ---.-,,.....,...,......,..,...,..,...,......,..,...,......,..,.....,......,..,..,...,..,1,,..,1.......,..,...,,..,...,...,..,....,..,....,..,.....-T.....,...,.........,....,..,.."P"'T"....,...,..,..T"'!"".,..,...,..,
1 1 1
t---l--t---l--t--l--t--l--t--l--t--l--t--l--H-I--H-l---rt_H-l---rt_rt_~--i_~~---tL~~---t---l---t----t-t-t
-t-t1_t-l---t----lt-...r---lH---IH----l'-1---IH---I----t---1----t---1----t---1----t----'---t---1----t---1----t---1----t---1----t---1----t---1----t---1----t---1----t---1----t---1-----t---1-----t--+----t--+---t--+--t--1----t--+---t--+--t--1---t-1-1----1
1
8
-------,;,,.;---'-t-__
..._l
Number of
megajoules of
energy needed
1- -
1- -
each day
--1- -
0 .................._
__._________.......__................-'---.......-
baby aged
3 months
child aged
8 years
..............~ _ . _ -.........___......._.....__.......__________...__....._....,
boy aged
15 years
girl aged
15 years
managed
50 years
woman aged
50 years
Person
239)
______1__
o_ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Questions
Use the bar chart in Figure 7 .2.1 to answer these questions.
1
2
3
4
5
How many megajoules of energy does an eight-year-old child need,
on average?
Explain why some eight-year-old children might need more energy
than this.
Explain why some eight-year-old children might need less energy
than this.
Suggest why a man aged 50 years needs to take in less energy in his
diet than a boy aged 15 years.
Suggest why most 15-year-old girls need less energy in their diet than
most 15-year-old boys.
Different diets
Everyone is different. Different people need different diets. Everyone
needs plenty of minerals and vitamins, but people vary in how much
protein and carbohydrate they need. Here are some examples.
Young people who are still growing need
a lot of protein to make new cells. If they
use a lot of energy, then they need to eat
enough carbohydrate to give them plenty
of energy. They need to eat a little bit of
fat, for energy and also for making the
membranes on the new cells.
People who have to sit down for a lot of
the day don't use up as much energy as
people who are very active. So they don't
need to eat as much carbohydrate or fat
as someone who has a job that involves
moving around, or who does a Jot of sport.
A pregnant woman needs to eat plenty of
protein to help to build her growing baby's
new cells. She also needs lots of iron in
her diet, to make haemoglobin in her own
blood and her baby's blood. She should eat
plenty of calcium, for building her baby's
bones.
240)
7 .2 A balanced diet
Fibre
As well as the six nutrients you need in your diet, you
also need to eat plenty of fibre.
Fibre is not actually a nutrient. This is because, when
you eat it, you cannot digest it. So it does not go into
the blood or to your cells. Instead, it just travels all
the way through the digestive system. It leaves the
body as faeces.
You might think this means that it is no use to you, but
in fact fibre is very important to keep the digestive
system healthy. It helps to prevent constipation, when
the digestive system slows down and faeces collect
inside it, instead of being passed out.
Fibre is mostly cellulose. Remember that plant cell walls are made of
cellulose, so foods made from plants are a good source of fibre. Cereal
grains, seeds and fresh fruit and vegetables are all excellent sources of
fibre. And the good thing about this is that these foods usualJy contain
lots of different minerals and vitamins, too.
Question
6
Copy and complete each of these sentences.
Choose the correct words from the brackets.
a
I need protein for (growth/energy).
b There is a lot of protein in (sugar/fish).
c
Starch and (sugar/fat) are carbohydrates.
d
I get energy from carbohydrate and (calcium/fat).
Food groups
It can be quite difficult to think about which nutrients are in each kind
of food that you eat. To make it easier, it sometimes helps to think about
food groups.
241 )
______
1_o_i_e_t_a_nd_g_ro
_w_th_ _ _ _ _ _ _ _ __,)
The picture shows some different kinds of food arranged in a triangle.
The bigger the area in the triangle, the greater the proportion of your
diet that kind of food should make up.
--------------1 Not too many sweets
or fried foods
Quite a lot of meat,
fish, eggs, pulses or
dairy products, for,
protein.
Lots of fresh fruit and
vegetables, for
minerals, vitamins
and fibre.
Plenty of rice, bread,
pasta - preferably
whole grain -for
starch and fibre.
Not too much
Although you should try to include every different kind of nutrient in
your diet, there are some things that you should not eat too much of.
•
Too much sugar (a kind of carbohydrate) can make your teeth decay.
It also increases the risk of developing an illness called diabetes.
•
Too much fat, oil or carbohydrate can make you put on weight.
This can put a strain on your joints, heart and other body organs.
•
Eating too many fats that come from animals can increase the risk
of developing heart disease.
242)
7 .2 A balanced diet
Activity 7 .2.1
Advice on a healthy diet
Work with a partner for this activity.
These five learners are all giving good advice about eating a balanced diet.
Think about what each person is saying.
Match each of the pieces of advice with one of these reasons.
1
This means that you will get some of each kind of nutrient, including all the
different vitamins and minerals.
2
These contain fibre and lots of vitamins.
3
This often contains a lot of fat from animals, and very few vitamins or minerals.
4
Not eating enough food will prevent the cells, tissues and organs in your body
having enough energy to keep hea lthy.
5
It can increase the risk of getting heart disease when you get older.
243)
______1__
o_ie_t_a_n_d_g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Questions
7
Look at the picture of the food triangle.
a
Explain why sweets and fried foods are at the top of the triangle.
b Explain why it is better to eat whole-grain bread, or brown rice,
rather than white bread or rice.
c
8
Suggest how you can make sure you get enough protein in your
diet, if you don't like eating meat or fish.
Your little brother's favourite meal is a burger and fries,
with a sweet milky drink.
a
What nutrients does he get from this meal?
b What else should he include in his diet?
c
Explain to him why he should not eat his favourite
meal too often.
Summary checklist
D I can explain what is meant by a balanced diet.
D I can explain why different people need different diets.
0 I can explain why no one shou ld eat too much sugar or fat.
7 .3 Growth, development and health
> 7.3 Growth, development
and health
In this topic you will:
•
learn how growth takes place
•
find out about the difference between growth and
development
•
think about how your diet and the amount of exercise you
take affects your growth, development and health
•
learn how smoking affects health.
n
~
Getting started
Key words
Most people know that doing plenty of exercise and not smoking
help you to stay healthy.
carbon monoxide
With a partner, think about these questions.
embryo
nicotine
1
How does doing plenty of exercise help to keep you healthy?
2
How does not smoking help to keep you healthy?
development
particulates
tar
______1__
o_ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Growth
Every person on Earth began their life as a single cell. This cell divided
to produce two cells. Each of these cells got bigger, then divided again.
0 - EE
A single cell
divides into two.
ffi
Each cell
grows.
The cells
divide again.
Each cell
grows.
To begin with, the cells are all the same. They produce a little ball of
cells ca!Jed an embryo, and eventually a baby.
This all happens inside the mother's body. By the time the baby is born,
it is a miniature human being. It continues to grow until it is about
18-20 years old.
Cells contain a lot of protein. Energy is needed to make cells divide.
A pregnant woman and a growing child need plenty of protein in their
diet, as well as enough energy to help cells to divide.
Development
The change from a single cell to an adult human involves more than just
growth. As the tiny embryo grows into a baby, all its different tissues
and organs are formed. As the baby grows into a child, its leg muscles
and bones become stronger, so that it can walk and then run. Its brain
develops, as it learns to talk and to play with toys.
These changes are called development.
Each person is an individual, and everyone grows and develops at
different rates, and in slightly different ways. But everyone goes through
the same stages in development. These are shown in the chart in. Notice
that each stage blends gradually into the next one - there are no sharp
divisions between them.
age in
years
baby
toddler
0
2
3
4
5
6
7
8
9
10
11
12
13
14
Questions
1
Growth means getting bigger. Explain what happens as a person
grows, to make their body get bigger.
2
Some young children do not get enough protein or energy in their
diet. Explain why they may not grow very tall.
246)
adult
adolescent
child
15
16
17
18
19
7 .3 Growth, development and health
Exercise and health
Topic 7.2 described some of the ways in which your diet can affect your
health. There are other ways in which the decisions you make abou t
your lifestyles can affect how healthy you are.
Taking regular exercise is a really good thing to do. This helps to use
some of energy in the food you eat each day, stopping you from storing
too much as fat. It also makes the heart and muscles work hard, so that
they become strong. Exercise can also make people feel more cheerful
and positive about life.
Smoking
Smoking cigarettes damages the smoker's health. It also damages the
health of people around them, who accidentally breathe in cigarette smoke.
Tobacco contains many different harmful substances.
Nicotine
Tobacco smoke contains nicotine. Nicotine can help someone to stay alert. Nicotine is addictive.
This means that it is difficult to manage without it, once you are used to smoking. This is why
smokers find it so difficult to stop smoking.
Nicotine damages the blood vessels in a smoker's body. It makes them get narrower, so it is harder
for blood to get through them. Smokers are more likely than non-smokers to develop heart disease.
Tar
Carbon monoxide
Tobacco smoke contains
a mixture of dark, sticky
substances called tar.
Some of the chemicals in
tar cause cancer. Cancer
happens when cells start
dividing out of control and
spread to other parts of the
body. Smoking increases
the risk of getting many
different kinds of cancer,
including lung cancer.
Carbon monoxide is a
poisonous gas. When it gets
into the body, it combines with
haemoglobin inside red blood
cells. This stops haemoglobin
doing its normal job, which is
to combine with oxygen and
transport it to all the body
cells that need it. So a smoker's
cells don't get enough oxygen.
They cannot carry out enough
respiration, so don't have
enough energy.
"
~
--r
Particulates
Tobacco smoke contains tiny particles of carbon and other materials, called particulates.
They get trapped inside the smoker's lungs. This makes the walls of the alveoli break down.
Instead of having millions of tiny alveoli in the lungs, the smoker has a lot of big spaces.
This is makes it difficult for them to get enough oxygen into their blood.
247 )
______1__
o_ie_t_a_n_d_g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Activity 7 .3.1
Why do people smoke?
Work in a group of three for this activity.
Until t he 1960s, no one realised that smoking was bad for your health. Today, everyone
knows how harmful it is.
In your group, discuss these questions. You might need to do some research to find
the answers to some of them.
•
Why do people choose to smoke? Do you think the reasons are different for older
people and younger people?
•
Why is it difficult to give up smoking, once you have started?
•
Why did it take so long for people to realise that smoking was harmful? In the
1940s and 1950s some cigarettes were advertised as being medically approved
and good for you. Find some data about smoking from the 1950s. Where did the
data come from? Was some of it biased? Why might tobacco companies have
tried to hide the dangers?
•
Is the government in your country trying to reduce the number of people smoking?
If so, what are they doing?
Be ready to share your ideas.
Questions
The bar chart in Figure 7.3.2 shows the percentages
of babies with a bi1ihweight lower than normal,
born to mothers who smoked different numbers Percentage of
of cigarettes per day while they were pregnant.
babies born
with low
Use the information in the bar chart to answer
birthweight
these questions.
3
4
5
What percentage of babies born to mothers
who do not smoke have a low birthweight?
Calculate the percentage of babies born to
non-smoking mothers that do not have a
low birthweight.
Describe how smoking during pregnancy affects the
chance of having a baby with a low birth weight.
Summary checklist
D I can describe how organisms grow.
D I can explain what is meant by development.
D I can explain why exercise is good for a person's health.
D I can explain how smoking damages health.
248 )
..
10
Ill
..
...,~-~_
,-~
" ~
,_
8
>- f -
,..":
6
f-
~
,..'.'.~
4
,-
f-
>-
f-
..... _.._
,-~
2 - 1-..
,- f,- f1- f-
f-
~
f-
I ~~
~
,_.,~
f-
,- ~
0
.._
none
less than 15
15 or more
Number of cigarettes per day smoked
by mother during pregnancy
7 .4 Moving the body
> 7.4 Moving the body
In this topic you will:
•
learn about hinge joints and ball-and-socket joints
•
find out how a pair of muscles moves the arm at the elbow.
Getting started
1
2
Some bones protect parts of the body. Look at the diagram
of the skeleton on the next page. Which bones do you think
are important for protection? What do they protect?
Some bones are important in movement. Which bones do
you think are important for movement?
words
antagonistic
muscles
ball-and-socket
joints
biceps
contraction
exoskeleton
hinge joints
joints
muscles
relax
skeleton
tendons
_ _ _ _ _ _1__
o_
ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
The skeleton
Animals' bodies are supported by a skeleton.
Insects and other arthropods have a skeleton
on the outside of their body. This is called an
vertebral column
clavicle
exoskeleton.
sternum
Your skeleton is inside your body. It is made
of bones. You do not need to remember the
names of all of these bones, but you may know
some of them already.
humerus
Bones are hard and strong. They contain a lot
of calcium. If you do not have enough calcium
in your diet, your bones may not grow properly.
Bones contain living cells, so you also need
protein in the diet to build strong bones.
radius
scapula
rib
ulna
carpals
femur
Joints
Bones cannot bend. Movement in the skeleton
can only take place where two bones meet one
another. T hese places are called joints.
Some joints work like the hinges on a door.
They let the bones move back and forth in
one direction, in the same way that a door
opens and closes. These are called hinge joints.
tibia - - - +
fibula _ _ _,....
The human skeleton
Some joints let the bones move in a complete circle. At these joints, one
of the bones has an end shaped like a ball. The other bone has a cup, or
socket, that the ball fits into. These are called ball-and-socket joints.
Activity 7.4.1
Identifying different kinds of joint
Work with a partner.
Look at the diagram of the skeleton. If you have a model of a skeleton, you could look
at that as well.
Can you find at least two different hinge joints on the skeleton? (You may be able to
find many more than two.) Try moving your own joints at these places. Which bones
meet at the hinge joints?
Now try to find two different ball-and-socket joints on the skeleton. Try moving your
own joints at these places. Which bones meet at the ball-and-socket joints?
Write down your ideas, and be ready to share them with the rest of the class.
250)
_Q)
7 .4 Moving the body
Questions
1
Explain what a joint is.
2
These pictures show a man hitting a golf shot.
a
Which hinge joints is he moving?
b Which ball-and-socket joints is he moving?
Joints in the arm
You have several different joints in your arms. These include the shoulder
joint, the elbow joint, the wrist joint and all the joints in the fingers.
The photo is an X-ray of someone's arm. Can you pick out the
humerus, radius and ulna? You should also be able to find the
hinge joint at the elbow, and the ball-and-socket joint at
the shoulder.
scapula (shoulder blade)
bal I-and-socket joint
humerus
wrist bones, with many
joints between them
radius
hinge joints in fingers
/
hinge joint at elbow
ulna
finger bones
hand bones
251 )
______1__
o_ie_t_a_n_d_
g_ro_w_th_ _ _ _ _ _ _ _ ___,)
Muscles
Bones and joints cannot move themselves. You use muscles to move
bones at joints.
Muscles are made of specialised cells. These cells are able to make
themselves shorter. This is called contraction.
Muscles use energy to contract. Like all cells, they get this energy from
nutrients, especially glucose. The energy is released from glucose by
respiration. The more you ask your muscles to contract, the more energy
they use, and therefore the more glucose they use.
Muscles can produce a strong pulling force when they
contract. Many of your muscles are attached to bones,
by tough cords called tendons. When the muscle
contracts, it pulls on the tendon, which pulls on the
bone. This makes the bone move at a joint.
scapula
This diagram shows the muscles that move the arm
bones at the elbow joint.
First, look at the biggest muscle in the diagram.
This is the biceps. (Biceps is an unusual word,
because it ends in an s even though it is singular.
One biceps, two biceps.) 'Bi-' means two. This
muscle is called the biceps because it has two tendons
that attach it to the scapula.
triceps muscle
The longer, thinner muscle in the diagram is the triceps.
Que stions
3
5
The biceps is attached to the scapula at one end.
Which bone is the other end attached to?
Which bones is the triceps attached to?
Tri- means three. Suggest why the triceps has this name.
6
Tendons are not stretchy. Suggest why.
4
252)
humerus
biceps muscle
7 .4 Moving the body
Bending the elbow joint
Think about what happens when you bend your
arm at the elbow.
When you decide to bend your arm, your brain
sends an electrical impulse along a neurone, to
your biceps muscle.
The cells in the biceps muscle respond to this electrical
impulse by contracting. This makes the whole muscle pulling get shorter.
force
The biceps muscle is firmly fixed to the scapula at
one end and the radius at the other end. So when
it gets shorter, these bones are pulled closer together.
The elbow bends, as shown in the diagram.
To bend the arm,
the biceps contracts
(gets shorter) and
the triceps relaxes.
--1-fiC--+-----\olr
The contracting
biceps pulls on
the tendon, so
the radius moves
upwards.
Activity 7.4.2
Feeling your muscles
You can do this activity on your own .
Rest your arm on the table in front of you, keeping it straight.
Put the fingers of your other hand on your upper arm, where
your biceps muscle is.
Slowly and steadily, bend your arm upwards.
Do this severa l times.
What can you feel happening in your upper arm, when you
do this?
Be ready to share your ideas.
Straightening the elbow joint
Now think about how you straighten your arm at the elbow joint.
It's important to remember that muscles can only pull. They
cannot push. Muscles can generate a force by getting shorter, or
contracting. But they cannot generate a force by getting longer.
So the biceps cannot push the arm straight again. You need
another muscle to pull the arm straight.
The muscle that does this is the triceps muscle. This diagram
shows how it does this.
When a muscle is not contracting, it relaxes. This is all that
muscles can do - they can either contract or relax.
To straighten the arm,
the triceps contracts
and t he biceps relaxes.
The contracting
triceps pulls on the
tendon, so the ulna
moves downwards.
253)
______
1_o_i_e_t_a_n_d_g
_r_o_w_t_h___________)
Antagonistic muscles
You can see that the biceps muscle and the triceps muscle work as a team.
To bend the arm, the biceps contracts and the triceps relaxes.
To straighten the arm, the triceps contracts and the biceps relaxes.
Two muscles that work together like this are called antagonistic muscles.
When one of them contracts, it moves the bones at a joint in one
direction. When the other muscle contracts, it moves the bones in the
other direction.
Think like a scientist
Using a model arm to investigate how the biceps muscle works
You are going to investigate how the size of the force produced by the biceps
muscle differs, if it is attached at different positions on the radius.
You will need:
• a model arm, like the o ne in the diagram
• some masses on a hanger
• a newton meter
Topic 3.4 showed that the arm acts like a lever. In this investigation, you are
going to try attaching the 'biceps muscle' at different points along the 'radius',
to find out the force needed to lift a weight.
Set up your model arm like this.
'humerus'firmly
attached to support
piece of wood or strong
cart to represent the
humerus bone
newton meter
'radius' attached to
'humerus'with freely
moving pivot
masses
hooks at 1O cm
intervals
254)
piece of wood or strong card to
represent the radius bone
C
7 .4 Moving the body
Continued
Method
1
Read through the method. Then construct a results chart to fill in your results.
2
Put some masses on the hanger. Start with just one or two masses. (Make sure you
record these masses in your resu lts table.)
3
Attach the newton meter to hook 1. Pull gently and steadily vertically upwards until
the 'radius' makes a right angle with the 'humerus'. Record the force reading on the
newton meter as you keep the radius in this position .
4
Now attach the newton meter to hook 2, and repeat.
5
Repeat again, with the newton meter attached to hook 3 and then hook 4 .
6
Put some more masses on the hanger. Repeat steps 4 to 6.
Questions
1
What does the newton meter represent in this model?
2
What happened to the force needed to keep the radius horizontal, as you moved the
newton meter further away from the elbow joint?
3
Use what you have learnt about turning forces (moments) in your physics lessons to
explain your answer to question 2.
4
What happened to the force needed to move the radius, when you added extra
masses to the hanger?
5
Use what you have learnt about turning forces (moments) in your physics lessons to
explain your answer to question 4 .
6
Which position - 1, 2, 3 or 4 - matches the position where the rea l biceps is attached
to the real radius?
7
Muscles can produce very strong forces when they contract. But they cannot make
themselves very much shorter. Suggest why the rea l biceps is attached in this position.
Summary checklist
(.)
D I can name the bones in the arm.
D I can identify some hinge joints and ball-and-socket joints in the body.
D I can describe how muscles produce a force when they contract.
D I can explain how the biceps and triceps work as antagonistic muscles to move the arm
at t he elbow.
255 )
7
Diet and growth
Check your progress
7 .1 A weightlifter asks his trainer for advice on his diet. The trainer gives this advice.
•
Eat some protein with every meal.
•
Eat plenty of starch or other carbohydrates.
a
Copy and complete the sentences. Choose words from the list.
constriction
contract
fat
relax
glucose
respiration
The weightlifter uses his muscles to lift weights. The muscles _ _ _ _ __
to make the weights move. This uses energy. The muscles get the energy by
breaking down _ _ _ _ _ _ in a reaction called _ _ _ _ __
[3]
b
Explain why the weightlifter needs to eat plenty of protein.
[2]
c
Explain why the weightlifter needs to eat plenty of carbohydrate.
[2]
d
List four other nutrients the weightlifter should include in his diet
as well as protein and carbohydrate.
[2]
7 .2 The graph shows the mean mass of girls at different ages.
60
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Mean mass/ kg
-r
30
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8
10
12
t
14
16
H
18
H
H
20
Age/ years
a
What is the mean mass of girls when they are two years old?
b
By how much does the mean mass increase between two years and
I O years old?
[1 ]
c
Between which ages does growth happen most rapidly?
[1 ]
d
Does the graph show that most girls have stopped growing by the age of 20?
Explain your answer.
[1 ]
7
Diet and growth
7 .3 The diagram shows the skeleton of a cat. Cats have the same bones as humans,
but their sizes are different.
a
b
Which joints, A, B, C or D , are hinge joints and which are ball-andsocket join ts?
Where should the two ends of a muscle be attached to move the
cat's front leg as shown by the arrow?
Choose from P, Q, R and S.
C
[11
[11
Where should the two ends of a muscle be attached to move the
cat's front leg back to its original position?
Choose from P , Q, R and S.
[11
What name is given to two muscles like the ones you have described
in band c?
[1 ]
Explain why two muscles are needed to move a bone in one direction
and then back again.
[2]
f
Name one mineral needed for the cat to form strong bones.
[11
g
Cats are predators. They eat other animals. Suggest where cats get
this mineral from, in their diet.
[1]
d
e
Project
Project: A diet for Mars explorers
In this project, you will evaluate issues that require scientific understanding.
Your task
You are going to work with everyone else in your class to produce a display about
feeding astronauts as they travel to Mars and back.
The National Aeronautics and Space Administration, NASA, is hoping to send people
to Mars by the 2030s. They have many problems to solve if they are going to achieve this.
One problem is how to feed the astronauts so that they stay healthy and strong during
the long trip. It would take up to three years to go to Mars and back.
Here are some problems and suggestions that are being discussed by scientists
and others.
•
NASA could send a spaceship loaded with five years'-worth of food to arrive on
Mars before the astronauts arrive. Would that work better than the astronauts
taking all their food with them?
•
It wou ld take up less space if the food cou ld just be pills, instead of 'real' food.
Would that work?
•
The bones and muscles of astronauts get smaller and weaker when they are in space
for a long time. Are there any kinds of food that might help to reduce this problem?
•
To get fresh vitamins, astronauts need to eat fresh p lant-based
foods. Could they grow plants on their spaceship? Could they
grow plants on Mars?
Work in a group of four or five. Choose one or two of these
problems - it would be good if different groups choose different
ones. Use the internet to find other people's ideas for solving
them. You might also have your own ideas.
Work with the other groups in your class to produce a
display about how to feed the Martian astronauts.
Chemical reactions
> 8.1 Exothermic reactions
In this topic you will:
•
learn about chemica l reactions that give out energy
•
p lan and carry out an investigation
Getting started
Key words
This word equation shows the reaction between carbon and
oxygen that takes place when carbon burns:
combustion
dissipate
exothermic
reaction
carbon
-
oxygen
+
carbon dioxide
fuel
Answer these questions and then compare answers with a
partner. Be prepared to share answers with the class.
oxidation
reaction
•
Name a reactant.
preliminary work
•
Name a product.
•
How many atoms make up a particle of carbon dioxide?
•
How many of these atoms are carbon?
•
How do you know that burning releases energy to the
environment?
8.1 Exothermic reactions
Burning
When something burns, a chemical reaction takes place. Burning
is a chemical reaction in which a substance combines with oxygen.
In a burning reaction, there are energy changes. The substance that
reacts with oxygen is called a fuel.
Fuels have a store of chemical energy. Charcoal, wood, coal,
natural gas and oil are examples of fuels.
When the fuel bums, the chemical energy is changed to thermal,
light and sound energy. The thermal, light and sound energy
dissipate (spread out) into the surroundings.
Burning requires oxygen, fuel and
heat (thermal energy)
Combustion is another term for burning.
Look back at the equation in Getting started. You can see that, during
the reaction, the atoms of carbon and oxygen join together in new ways.
When this happens, chemical energy is changed to thermal energy and
the temperature rises.
A chemical reaction in which thermal energy is given out is called an
exothermic reaction.
Questions
1
What is needed for combustion to take place?
2
What is an exothermic reaction?
3
How can you tell that burning is an exothermic reaction?
261 )
______
a_ c_h_e_m_ic_a_l_re_a_c_t_io_n_s__________)
Burning other substances
Hydrogen can be used as a fuel in a model rocket. The combustion
of hydrogen is an exothermic reaction. The hydrogen and the oxygen
combine to form water.
hydrogen +
hydrogen
+
oxygen
~
water
oxygen
------+
water
When the atoms of hydrogen and oxygen rearrange themselves and
combine together, energy is given out. This chemical energy is changed
into kinetic, thermal, sound and light energy.
bent paperclips
string
to spark generator
mixture of
hydrogen and air
Burning hydrog en can prope l a plastic bottle like a rocket.
In this experiment, a large plastic soda bottle filled with hydrogen and
air is attached to a string across the room. The stopper in the bottle has
wires that allow a spark to be generated. The bot spark provides the
energy to start the reaction. The hydrogen and oxygen react together.
The reaction gives out a lot of energy and the stopper is pushed out.
This energy makes the bottle shoot (move very quickly) along the string.
262)
8.1 Exothermic react ions
The reactions of other substances burning in air are also exothermic
reactions. An example is burning magnesium, which produces magnesium
oxide. Energy is given out as heat and light as the magnesium and oxygen
atoms rearrange themselves.
magnesium
-
oxygen
+
magnesium oxide
When a substance burns, it combines with oxygen and a new substance
called an oxide is formed. Any reaction in which a substance combines
with oxygen is an oxidation reaction.
Burning magnesium ribbon
An exothermic reaction with water
This is the equation for the reaction between potassium and water.
potassium
+
water
potassium hydroxide
+
hydrogen
Water is made up of particles containing atoms of hydrogen and oxygen.
In the potassium and water reaction, the bonds between the atoms of
oxygen and hydrogen in the water break. The atoms rearrange to form
the products potassium hydroxide and hydrogen. Stored chemical energy
is changed to thermal energy, which dissipates into the environment.
263)
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
An exothermic reaction with acid
If you add magnesium to dilute hydrochloric acid the test tube gets hot.
This reaction is an exothermic one.
~
magnesium
+
hydrochloric acid
------.
magnesium chloride
+
hydrogen
Measuring the rise in temperature during a reaction
Sofia and Marcus each measured 10cm3 of dilute
hydrochloric acid into a test tube and measured the
temperature. Then they each added an identical piece
of magnesium ribbon to their test tube of acid.
When the reaction stopped,
they each measured the
temperature again.
M easuring t he rise in t em perature when m agnesium reacts w ith hyd ro chloric acid.
=
Sofia's results
M arcus's results
--
Start temperature
in °C
End temperature
in °C
Start temperature
in °C
End temperaturP
in °C
18
42
21
45
la ,;;
"'
Questions
4
What are the products when magnesium and hydrochloric acid react?
5
How did Sofia and Marcus know when the reaction had finished?
6
Marcus thought that more chemical energy had been changed to thermal energy by his
reaction because, in his experiment, the end temperature was higher. Sofia thought that both
reactions changed the same amount of chemical energy to thermal energy. Whose idea is
correct? Explain why?
264 )
8. 1 Exothermic reactions
7
Explain why it is a good idea to wear safety glasses whilst carrying
out this investigation.
8
Sofia and Marcus wondered how they could produce a higher
temperature change. Their ideas included adding more magnesium,
using a different metal and using a different acid.
Write each of these three ideas as a scientific question to be
investigated.
Think like a scientist
Planning and carrying out an investigation into the reaction between acid
and magnesium
Method
1
Choose one of the scientific questions to be investigated from question 8
(or write one of your own) and write a plan for your investigation.
•
Before you write your plan, try out the reaction between magnesium
and an acid. In this preliminary work you should practise measuring the
temperature change.
•
Decide what equipment you will need and make a list.
•
You also need to find out how big a change in the variable (for example,
the length of the magnesium ribbon) is needed to make a change in the
temperature that you can measure.
•
When the reaction takes place and chemical energy is changed to thermal
energy, the thermal energy dissipates (spreads out) into the environment.
o
Are you sure that you are measuring the temperature change accurately?
o
What could you do to reduce this heat loss?
•
Decide how you will record and present your results.
•
Carry out a risk assessment.
2
Ask your teacher to check your plan.
3
Carry out your plan. You may find that you want to make changes to it once you
begin doing the investigation. If so, write down the changes that you have made
and explain why you made them.
Questions
1
What can you conclude from your results?
2
Compare your results with others from the class. Are your results in agreement
with others who carried out the same investigation?
3
How could you improve your investigation?
265 )
______
a_c_h_e_m_ic_a_l_re_a_c_t_io_n_s__________)
How can preliminary work help me to improve my investigation?
I can describe what happens in an exothermic reaction.
I can plan an investigation.
I can carry out an investigation safely.
8.2 Endothermic reactions
> 8.2 Endothermic reactions
In this topic you will:
•
learn about chemical reactions that absorb energy
•
distinguish between exothermic and endothermic reactions
and processes
•
learn about the use of exothermic and endothermic reactions
and processes
Getting started
Key words
When you make any scientific measurements, you are told that
you need to be accurate and precise.
endothermic
process
What do you th ink this means? Discuss it with your partner.
endothermic
reactions
•
Look at these three archery targets.
•
If you are being accurate, where should your arrows hit
the target?
•
If you are being precise, shou ld all your arrows be near
to one another or spread out?
•
Which archer has been precise but not accurate?
•
Which archer has been neither precise nor accurate?
•
Which archer has been both accurate and precise?
Share your answers and ideas with the class.
267 )
______a__c _h_e_m_ic_a_l_r_ea_c_t_io_n_s_ _ _ _ _ _ _ ___,)
Endothermic reactions
Some chemical reactions absorb thermal energy from their surroundings
and change it to chemical energy stored in the chemical bonds. These are
called endothermic reactions. When an endothermic reaction takes place,
the temperature at the end of the reaction is lower than that at the start
of the reaction.
Think like a scientist
Carrying out an endothermic reaction
You will need:
• a test tube
• test tube rack
• lemon juice or citric acid
• stirring rod
• thermometer
• sodium hydrogen carbonate
• spatula
• safety glasses
Method
1
Place some citric acid or lemon juice in a test tube so that it is about
half full .
2
Measure and record the temperature.
3
Add three spatulas of sodium hydrogen carbonate and stir. Do not
use the thermometer to do this.
4
Measure and record the temperature.
Questions
1
What was the difference between the temperature at the start and the
end of the experiment?
2
Is thermal energy given out to the surroundings or taken in from the
surroundings during this reaction?
Looking at endothermic reactions
This is the word equation for the reaction between sodium hydrogen
carbonate and citric acid:
sodium hydrogen carbonate+ citric acid-... sodium citrate+ water+ carbon dioxide
During this reaction, thermal energy is absorbed from the surroundings
and stored in the form of chemical bonds. So, if this reaction was carried
out in a test tube, the surroundings will have a lower temperature and
the test tube will feel cooler.
268)
"(
f
(
8.2 Endothermic reactions
If you eat sherbet sweets, this reaction takes place in your mouth. The
sherbet is a mixture of dry citric acid and sodium hydrogen carbonate.
When you eat the sweets, these substances dissolve in your saliva,
and react together. This gives a cool 'fizzy' feeling in your mouth (the
surroundings), which is refreshing.
Questions
1
What are the reactants in the reaction shown in the word
equation above?
2
Which are the products in the reaction shown in the word
equation above?
3
What is an endothermic reaction?
4
Explain why eating sherbet sweets makes your mouth
feel cooler.
5
You may also get a 'fizzy' feeling in your mouth when you
eat sherbet. Why is this?
Another way to cool down
If you place about of water in a beaker and then stir in three
spatulas of potassium chloride, you will find that the beaker gets
cold. In this case, no chemical reaction has taken place. No new
products are formed. The potassium chloride has just dissolved.
A solution of potassium chloride has been fo rmed. Potassium
chloride is the solu te and water is the solvent.
potassium - -----=qi,ollil
chloride
When potassium chloride dissolves in water, thermal energy
is absorbed from the surroundings. This is why the beaker
feels cold. This is an endothermic process.
Ice melting is another endothermic process. Thermal energy
is absorbed from the surroundings as the solid ice changes
to liquid water. Think about what happens to the particles
when water changes state. The particles in the ice are lined
up in rows and can only vibrate about fixed positions - they
cannot move around inside the ice. The forces between the
particles are strong.
I energy
t taken in
--✓
--
As the particles absorb thermal energy from the surroundings, they
vibrate more and more. The ice begins to melt. When the particles have
enough energy, they can move and overcome the forces holding them in
place. The particles can now slide past one another. The water is now in
a liquid state.
269)
______
a_ c_h_e_m_ic_a_l_re_a_c_t_io_n_s__________)
Questions
6
Why is ice melting called an endothermic process and not an
endothermic reaction?
7
Suggest a change of state, other than ice melting, that is an
endothermic process.
8
When you have been swimming and you come out of the pool, you
may feel cold. Use your understanding of endothermic processes to
explain why.
9
Suggest whether water freezing is an endothermic or exothermic
process. Can you explain your suggestion?
Endothermic or exothermic?
In exothermic reactions and processes, thermal energy is given out.
In endothermic reactions and processes, thermal energy is taken in.
\ I
""'
boiling water
cooling
~
\ I
heat given out
~
heat taken in
JI.-T-fafa--4 ~
ice melting
,..-,-.._,--..
Exoth ermic processes g ive out energy to t he surroundings (left). Endot hermic processes absorb energy from th e
surro undings (right).
Think like a scientist
.-
Endothermic or exothermic?
In this series of experiments, you will try some of reactions and processes and
decide if the reaction or process gives out energy to the surroundings or absorbs
energy from the surroundings.
You will need:
• beakers or polystyrene cups or other insulated containers
• stirring rod
• thermometer (do not use the thermometer for stirring the solutions)
• chemicals as listed below
270 )
• safety glasses
'
8.2 Endothermic reactions
Continued
Suggested reactions and processes to try
1
Sodium hydroxide and dilute hydroch loric acid.
2
Potassium chloride and water.
3
Melting ice cubes.
4
Copper sulfate solution and magnesium powder.
5
Ammonium nitrate and water.
6
Boiling water until steam comes off.
7
Steam from a kettle directed at a co ld surface.
8
Dilute hydroch loric acid and magnesium ribbon .
9
Sodium hydrogen carbonate and citric acid.
fC
polystyrene cup
containing liquid
Method
Carry out some or all of the reactions or processes suggested.
Make sure you do a risk assessment for each test that you do.
1
Construct a results table.
2
Place one of the solutions in the beaker or polystyrene cup.
3
Measure and record the temperature.
4
Add the other substance.
5
Allow the substances to react, dissolve or change.
6
Measure and record the temperature.
7
Clean the thermometer and the g lass rod before using them for the next test.
8
For each test you did, say if it is endothermic or exothermic and if it is a reaction
o r process.
Questions
3
What advantage is there if a polystyrene cup is used rather than a glass beaker?
4
Which reaction gave out the most energy to the surroundings?
5
Which reaction absorbed the most energy from the surroundings?
6
Did you have d ifficulty measuring the temperature with any of these reactions
or processes? Explain how you could decide if the reaction or process was
exothermic or endothermic if you could not measure the temperature.
271 )
______
a_ c_h_e_m_ic_a_l_re_a_c_t_io_n_s__________)
Using exothermic reactions
Some exothermic reactions are used to produce
self-heating cans of food or drink. For example, a can
of self-heating food contains two chemicals, which are
in separate compartments. When you open the can,
the two chemicals mix with each other and react. The
reaction warms up the food or drink.
opening system
seal for water and calcium
oxide compartments
water
waterproof separator
calcium oxide
heat insulator
The chemicals used are calcium oxide and water. When
the water and calcium oxide are mixed together they react,
and heat is given off.
calcium oxide + water --.. calcium hydroxide
These cans can be very useful if you are in a remote
area, or in an emergency when there is no power, or
when you are camping.
A self-heating can. When the can is opened, the
seal between t he water and the calcium oxide
compartment is broken and t he reaction takes
place. Thermal energy is given out and t ransferred
to the food.
The cans are expensive to produce because the
compartments must be sealed from one another and from the food,
so that it does not become contaminated. There have also been problems
with the food not being heated evenly.
Using endothermic processes
People sometimes use ice packs when they injure
themselves. These packs are stored in a fridge or freezer
until they are needed. When the ice pack is placed on the
injured area, heat from this area is transferred to the ice
pack and the ice melts. This is an endothermic process.
not an endothermic reaction as no new substances are
formed It means that the injured area is cooled and this
often prevents it from swelling up. After it has been used,
the ice pack can go back into the freezer to be used again.
A chemical icepack being used to treat an inj ury.
Some 'ice' packs are made from substances that undergo
an endothermic process when they mix together.
These packs can be used even when you don't have fridge or freezer.
The pack has two compartments inside, each with a different substance.
These are usually ammonium nitrate and water. When you push on the
pack and break the compartment containing ammonium nitrate, the
water mixes with it and the ammonium nitrate begins to dissolve. This is
an endothermic process, so the temperature drops.
272)
8.2 Endothermic reactions
Questions
7
Explain why self-heating cans are very expensive.
8
Explain why a self-heating food container can only be used once.
9
Describe one advantage and one disadvantage of each of the two
types of icepack described above.
What exothermic and endothermic reactions do I use in my
everyday life?
Su mmary checklist
D I can list some chemical reactions that are endothermic.
D I can explain the difference between an endothermic reaction and
an exothermic process.
D I can carry out an investigation to distinguish between exothermic
and endothermic reactions and processes.
D I can describe some uses of exothermic and endothermic reactions
and processes.
273)
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
> 8.3 Metals and their
reactions with oxygen
In this topic you will:
•
describe the reactions of some metals with oxygen
•
carry out an investigation
•
compare how reactive some metals are with oxygen
Getting started
Key words
Think about what you learned about the properties of metals in
Stage 7. In one minute, write down all the properties you can
remember. Compare your list with a partner and add any new
ones to your list. Then compare your new list with another pair
and add any more properties. Be prepared to share your list
with the class.
collapses
inert
p revent
reactive
rusts
8.3 Metals and their reactions with oxygen
Metals and oxygen
In Stage 7 you learned about the properties of metals. Now you are
going to investigate how different metals react with oxygen.
Think like a scientist
Heating metals in air
In this activity, you will heat several different metals in air. Air contains oxygen,
and some metals wi ll react with it.
Read though the instructions and decide on the safety precautions you will need
to take. Discuss these in your group and then with the class before you carry out
your investigation.
You will need:
• safety glasses
• Bunsen burner
• heatproof mat
• tongs
• small pieces of metal such as magnesium, zinc, iron and copper
Method
1
Take a small p iece of one of the metals.
2
Place it in the tongs and heat it in a Bunsen flame.
3
Record your observations in a table and explain what
happened.
4
Repeat steps 1-3 for each of the other metals provided.
Questions
1
Which was the most reactive metal that you used? What evidence do you
have for this?
2
What safety precautions did you take?
3
Suggest why were you not given metals such as sodium or potassium to heat.
4
Suggest why were you not given metals such as gold or silver to heat.
275 )
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
Looking at the reactions of metals
with oxygen
Many metals react with oxygen if they get hot enough. When you look
carefully at the reactions of metals with oxygen, it is possible to identify
which metals are more reactive. For example, magnesium is more
reactive than iron because magnesium reacts more quickly than iron.
This reaction between metals and oxygen is an oxidation reaction.
Some metals react very quickly with oxygen without even being heated.
When pieces of sodium, potassium or calcium are taken from their
containers, they appear dull. When the pieces are cut, the surface is
shiny. The shiny surface soon becomes dull because the metal reacts with
the oxygen in the air. The surface becomes covered with a new substance
- the oxide of the metal. These metals are so reactive that they have to
be stored under oil to prevent them reacting. The layer of metal oxide on
the surface prevents any more of the metal from reacting with the ai r or
water vapour.
A scientist cuts a piece of sodium metal with a scalpel.
The general word equation for this reaction is:
metal + oxygen -.- metal oxide
Some metals, such as gold, do not react with oxygen. They are generally
unreactive. They are described as inert.
Silver reacts slowly with the air and if a siJver object is not cleaned it
goes black over time, as silver oxide is formed.
276)
8.3 Metals and their reactions with oxygen
Questions
1
Which property for sodium and potassium is not typical of a metal?
2
Why is the scientist in the photograph wearing gloves to cut this
piece of sodium?
3
Write a word equation for the reaction between sodium and oxygen.
The reaction between iron and oxygen
When iron is left in damp air it rusts. The iron reacts with oxygen to
form an orange-brown solid, called iron oxide, otherwise known as rust.
iron + oxygen - . iron oxide
This is not a very useful reaction because it means that the iron changes
and no longer has the same properties. A strong iron girder can become
rusted and fall apart. This could mean that a building collapses.
The reaction between iron and oxygen only takes place when both water
and oxygen are present. The water is not part of the equation, but it is
needed for the reaction to happen. The reaction takes a long time to
happen - iron is not very reactive with oxygen.
This new iron spanner, nuts and b olts are shiny.
The iron sheets in this old barn have rusted.
277 )
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
What causes iron to rust?
A new iron nail is placed in each of four test tubes, as in the diagram.
After a few weeks
the experiment
looks like this.
tube 1
tube 2
tube 3
tube4
tube 1
tube 2
tube 3
tube4
Test tube 1 contains nothing, apart from the nail, and is open to the air.
Test tube 2 contains water and the nail is half in the water. The tube is
open to the air. So, this tube has air and water.
Test tube 3 has calcium chloride in the bottom. The calcium chloride
absorbs water so the air inside the tube is dry. The tube is stoppered.
Test tube 4 has water that has been boiled to remove as much dissolved
gas as possible. On top of the boiled water is a layer of oil. This stops
any air entering the water. The tube is stoppered.
Tube number
Contains
Result
1
moist air
nail is rusted
2
water and air
nail is very rusty
3
dry air
no rust
4
boiled water covered with oil, no air
small amount of rust
'"-
h,
,.
.. ,
F
(.!
Questions
4
What conditions are needed to prevent iron from rusting?
5
Which test tube and which conditions caused the iron to rust
most quickly?
6
Why is the same type of nail used in all test tubes?
7
How is the air in tube 3 dried?
8
How is the air in tube 4 kept out of contact with the nail?
278)
8.3 Metals and their reactions with oxygen
How can iron be protected?
There are ways that iron can be protected so that it does not rust.
The iron can b e painted . This stops t he oxygen in the air
reaching the iron.
The iron can be galvanised. This means covering t he iron
with a layer of zinc. This again prevents the oxygen reaching
t he iron.
Why do we need to reduce the rusting of iron?
Summary checklist
D I can describe the reactions of some metals with oxygen.
D I can carry out an investigation safely.
D I can compare how reactive some metals are with oxygen.
279)
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
> 8.4 Reactions of metals
with water
In this topic you will:
•
describe the reactions of some metals with water
•
carry out an investigation
•
compare how reactive of some metals are with water
Getting started
Think back to the reactions of metals with oxygen, that you
studied in Topic 8.3. Write down the name of the most reactive
metal you learnt about and try to make a list of the other metals
in order of how reactive they are. Compare your list with a
partner and make one list to share with the class.
reactivity
sandpaper
8.4 Reactions of metals with water
Think like a scientist
Reactions of metals with water
It can be difficult to see how some metals react with water because they may be
covered in a surface layer of metal oxide if they have reacted with the oxygen in
the air. In the investigations, you may need to use sandpaper to clean the surface
of the metals so that the metal can come in direct contact with the water.
You will need:
• test tubes
• test tube rack
• sandpaper
• forceps
• small pieces of metals such as magnesium, zinc, iron and copper
Method
1
Take a small piece of one of the metals you have been given.
Use sandpaper to clean the surface of the metal.
2
Place the metal into a test tube of water.
3
Record your observations in a table and explain what
happened. You may need to leave the metal to react
for some time. If nothing happens, you could try
testing the metal again, this time using hot water.
4
Repeat steps 1- 3 for each of the other metals you
have been given.
Questions
1
Which was the most reactive of the metals you were given?
What evidence do you have for this?
2
Use the results of your experiment to arrange the metals in order of
their reactivity, starting with the most active.
3
Suggest why some metals will react with hot water but not cold.
281 )
______
a_ c_h_e_m_ic_a_l_re_a_c_t_io_n_s__________)
Reactions of sodium and potassium
with water
Some metals are too reactive for you to test in water. Sodium and
potassium react very vigorously. They have to be stored under oil to
prevent them from reacting with the water vapour in the air.
Sodium reacts vigo ro usly with water.
Potassium is even more reactive t han sodium. So much
t hermal energy is g enerated that the hydrogen g as
p ro duced in t he reaction catches fire.
In these two reactions the metal reacted with water to produce hydrogen
and the metal hydroxide.
metal + water __.. metal hydroxide + hydrogen
Questions
1
Write the word equation for the reaction between sodium
and water.
2
What safety precautions must be taken when these reactions
take place?
3
Explain why these metals are stored under oil.
282)
8.4 Reactions of metals with water
Reactions of other metals with water
Some other metals react less vigorously with water - for example,
calcium and magnesium. In the experiment shown in the diagram,
a piece of calcium has been placed at the bottom of a beaker and
covered with water. A filter funnel has been placed upside down
over the metal. The gas given off is collected in a test tube by the
displacement of water.
----,----.-t--
-
-
bubbles of gas
Questions
4
What is the gas that is given off? How would you test for it?
5
How could you tell if calcium or magnesium is more reactive?
6
What factors should you take into account to make this a
fair test?
7
Write the word equation for the reaction between calcium and water.
Some of the metals that do not react with water may react with steam.
Even magnesium will react more rapidly with steam than with water.
In the reaction shown here, magnesium is heated.
From time to time, the heat is directed at the
ceramic wool. The ceramic wool has been soaked
in water, which when heated produces steam. In
this reaction the magnesium reacts with water,
which is in the form of a gas. Magnesium oxide
and hydrogen are formed. Tbe hydrogen gas that
is given off can be burnt.
hydrogen
gas burning
magnesium
ribbon
ceramic
wool
I..._.
===~:
heat
Heating magnesium
The word equation for this reaction is:
magnesium + water (g) ----. magnesium oxide + hydrogen
In the equation above the (g) after water indicates it is water in the form
of a gas, in this case steam. Steam is formed by boiling water and is very
hot whereas water vapour is made up of water particles in the air at
lower temperatures. Some metals, such as gold, do not react with water
at all.
Questions
8
Explain using particle theory, why the reaction between steam and
magnesium is more vigorous than between water and magnesium.
9
Which metals do not react with water? Name three.
10 If an element is said to be inert, what does it mean?
283)
______
a_c_h_e_m_ic_a_l_re_a_c_t_io_n_s__________)
Summary checklist
D I can describe the reactions of some metals with water.
D I can carry out an investigation safely.
D I can compare how reactive some metals are with water.
8.5 Reactions of metals with dilute acids
> 8.5 Reactions of metals
with dilute acids
In this topic you wil l:
•
describe the reactions of some metals with dilute acid
•
plan an investigation
•
carry out an investigation safely
•
compare how reactive some metals are with dilute acid
Getting started
Key words
You have 2 minutes to write down and complete as many of
these word equations as you can.
reagents
•
oxygen + sodium - . .
•
oxygen + magnesium - . .
•
oxygen + iron - . .
•
water + potassium - . .
•
water+ calcium - . .
•
magnesium + steam - . .
,--
salt
Check your partner's work. Be prepared to share your answers
with the class.
285 )
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
A familiar reaction
You will probably remember the reaction of magnesium with dilute
hydrochloric acid. This is the word equation for this reaction:
magnesium+ hydrochloric acid -
magnesium chJoride + hydrogen
Magnesium chloride is an example of a salt. When a metal reacts with
an acid, the products are a salt and hydrogen.
The general equation for this reaction is:
metal + acid -
salt + hydrogen
Questions
1
Write the word equation for the reaction between magnesium and
sulfuric acid.
2
What is the salt produced in the reaction in question I?
3
Describe what you would observe if this reaction took place in
a test tube.
4
Write the word equation for the reaction between zinc and nitric acid.
r
Think like a scientist
An investigation into the reaction of metals in acid
Sofia and Marcus have been asked to investigate the reactivity of metals with acids.
They need to decide on which of the equipment and reagents that are available in the
laboratory they need, to enable them to carry out the investigation as shown below.
~·
e-""
!"90
a-IHI
i-11
, j-oe
: i-~
• ;.<tO
; i,,.
•' .Ii D
;
•
IO
[l
safety
scree n
ll
~~"
safety~
glas.ses
286)
face protector
Metals :mch a>.sodium. pota~::.iurii.
magne..:~···, ......t.:~···, _;, -~. ~wr-r-~,. Jnd iron
in the form of bloc~ . riH;;9.; .:;,; .:,,:;,~·-,:det
8.5 Reactions of metals with dilute acids
Continued
Part 1: Planning the investigation
Use the information and ideas above to plan the investigation for Sofi a and Marcus.
Choose which of the items in the diagrams they need to use. Some of the items
are not appropriate to use.
Discuss in your small group how you will answer these questions.
•
What will they change?
•
What will they keep the same?
•
How will they measure the reactivity and decide which is the most or least
reactive metal?
•
How will they keep safe?
•
What equipment wi ll they use?
Remember to include a resu lts table and an idea of what they should be looking
for in order to identify which are the most reactive metals.
Write your p lan and show it to your teacher.
Questions
1
Which of the metals shown, should not be used by Sofia and Marcus? Explain why.
2
Explain which measuring cylinder they should use to measure out enough acid
to use in this investigation.
Part 2: Carrying out the investigation
Your task is to find the order of reactivity of the metals you are given, remember to
work in a methodical way and keep an accurate record of your results.
Method
1
Follow the plan you have written, once you have
had it checked by your teacher. Remember to
work carefully and to keep an accurate record of
your results.
2
Select the appropriate equipment.
Questions
3
Which metal was the most reactive in dilute acid?
4
Which metal was the least reactive in dilute acid?
0
287 )
______a__c_h_e_m_ic_a_l_r_e_ac_t_io_n_s_ _ _ _ _ _ _ ___,)
Activity 8.5.1
Reactivity order
On seperate sticky notes, write the name of each of the metals
you used when carrying out the investigation into the reaction
of metals in acid.
Stick these on to the table in the order of reactivity, with the
most reactive at the top. Use the information from the
investigation above.
Compare your order with other groups. Are they the same
or simi lar?
Use the class results to make an order you all agree on.
Does this order t ie in with the resu lts from the investigations of
the reactions of metals with oxygen and water?
Now write sticky notes for the metals you could not use (sodium,
gold, silver, calcium and potassium) and fit those into your list.
When you are happy with your order, make a poster to show your
list and illustrate it with d iagrams to show the various reactions
with oxygen, water and/or dilute acids.
Questions
5
Which was the most reactive of the metals you used?
6
How did you decide which of the metals in the list was the
least reactive?
How did the three investigations help me to decide in which
order to put the metals?
Summary checklist
D I can describe the reactions of some metals with dilute acid.
D I can plan an investigation.
D I can carry out an investigation safely.
D I can compare how reactive some metals are with dilute acid.
288)
Check your progress
8.1 Match these words or phrases to the descriptions, a, b, c, d and e.
Each word or phrase may be used once, more than once or not at all.
burning
evaporat1<.,
decreases
melting ice
endothermic
increases
exothermic
magnesium ribbon placed in hydrochloric acid
sodium hydrogen carbonate added to citric acid
a
An example of a chemical reaction where thermal energy is given out
to the surroundings
[1]
b
An example of an endothermic reaction
[1]
c
The temperature in an endothermic reaction
[1]
d
An example of an endothermic process
[1 ]
e
The type of reaction between calcium and water
[1 ]
8.2 Burning is a chemical reaction where thermal energy is
given out to the surroundings. Marcus has four fuels to
investigate to find out which gives out the most thermal
energy to the surroundings. He uses apparatus like this:
a
Which variable will Marcus change?
[1]
b
Name two variables Marcus must keep
the same.
[2]
Explain what he must do in order to be
able to identify which fuel gave out the
most thermal energy to the surroundings.
[2]
Name one safety precaution he should take
whilst carrying out this investigation.
[1]
c
d
fuel in
8.3 Copy and complete the following word equations.
spirit burner
a
carbon + .. . ----+- carbon dioxide
[1 ]
b
sodiu m hydroxide + ... ----+- sodium chloride + ...
[2]
c
... + oxygen - . . magnesium oxide
[1]
d
potassium+ water-.. ... + ...
[2]
8
Chemical reactions
8.4 Zara and Arun are carrying out an investigation into the heat given off
when they add pieces of calcium to water. They both use water and
add pieces of calcium.
These are Zara's results.
Mass of calcium
added in g
Start temperature
in°C
Final temperature
in °C
1
2
19
19
20
21
3
19
22
4
19
23
Mass of calcium
added in g
Start temperature
in°C
Final temperature
in °C
1
2
21
21
22
22
3
21
24
4
21
25
Temperature
change in °C
These are Arun's results.
)
Temperature
change in °C
~
=--= ,
F'
a
What trend is shown by both sets of results?
[1]
b
Predict what would happen if of calcium were added.
[1]
C
Complete the table for both of the student's results.
[2]
d
Construct a summary table to show the mean temperature change for
each mass of calcium used. (Your table does not need to show the
start and final temperatures).
[2]
Zara and Arun plot a graph of their results. Which variable and unit
should they put along the horizontal axis?
[1]
f
Which variable and unit should they put on the vertical axis?
[11
g
Zara and Arnn carried out a third set of experiments, using water
instead of . Could they use these results to add to the first two sets,
to calculate the mean temperature change? Explain your answer.
(2]
e
Project
Project: Working with chemicals safely
Background
Each day you make decisions about how to keep safe and minimise the risks that you
take. It might be when you cross a street, when you make a hot drink, head a football,
cook a meal or use a knife to cut vegetables. You probably don't even real ise you are
doing it, but you are carrying out a risk assessment for most tasks.
In the laboratory there are a number of hazardous situations and there are rules about
how you should behave and what you should do to stay safe. In the picture above there
are lots of things happening that are unsafe. People should never behave like that in a
laboratory, so look carefully at the picture and identify as many things that are unsafe as
you can.
Your task
You should be able to explain why a thing is unsafe. Work in a group of three or four and
make a list, with reasons.
Your main task is to provide guidance to learners starting the secondary science course, to
help them keep safe. You cou ld write a poem or a song that could be on every laboratory
wal l or in every child's notebook; you could write a guide book; write and perform a short
play or make a poster that could be in every laboratory. You should try to come up with
some original way of getting the safety message across.
Your work will be shared with the whole class.
Magnetism
>9.1 Magnetic fields
In this topic you will :
•
describe a magnetic field
•
understand that magnetic fields surround magnets
•
understand how magnetic fields interact
Getting started
Key words
Work in pairs. Make a list of places where magnets are used.
compass
like poles
~
.
magnet
magnetic
magnetic field
magnetic field
!Ines
l
9 .1 Magnetic fields
The magnetic field
A magnet is something that will attract magnetic
materials. Magnetic materials include the metals iron,
steel, nickel and cobalt. You will probably have used a
magnet to attract paperclips.
The paperclips are made from steel, which is a
magnetic material.
Magnets have two poles, north and south. They are
shown with the letters N and S on diagrams.
When a paperclip is close to one of the poles of a magnet, the paperclip
will be attracted to the magnet. As you move the paperclip further away,
it stops being attracted.
The paperclip is attracted to a magnet when it is in the magnetic field of
that magnet.
A magnetic field is the area around a magnet where the effects of the
magnet can be detected.
A magnetic field surrounds all magnets. The magnetic field of a magnet
is strongest at the poles.
- - - -- - - -
v.
7
magnet
paperclip
The paperclip is outside the magnetic fie ld of this magnet, so will not be attracted.
You can detect a magnetic field in two ways. You can see whether
a magnetic object moves because of attraction. You can also use
a compass. A compass contains a magnetised needle that is free
to turn. The needle will turn and point in the direction of a
magnetic field. The picture shows a compass. Some mobile
devices such as phones have compass apps.
Magnetic field lines
You can draw magnetic field lines around a magnet to represent
the magnetic field.
The rules are that
•
magnetic field lines join opposite poles
•
the magnetic field lines have arrows that point N ➔ S
•
magnetic field lines must not touch each other
•
magnetic field lines must not cross each other.
A compass can be used to detect a
magnetic field.
293)
______
9_M_a_g_n_et_i_sm
_ _ _ _ _ _ _ _ _ _ _ _ _)
Following these rules, the magnetic field lines around a bar magnet look
like this:
and the magnetic field lines around a horseshoe magnet look like this:
You can tell by looking at magnetic field lines where the magnetic
field is strongest. The magnetic field is strongest where the lines
are closest together.
If one magnet is stronger than another, the magnetic field of the
stronger magnet will be different in two ways.
•
All the field lines will be closer together.
•
The field lines will extend further away from the magnet.
You can also tell, by looking at magnetic field lines, in what
direction a compass will point. When it is in a magnetic field, a
compass will point in the direction of the lines.
294)
The five small compasses are pointing
in the direct ion of the magnetic fie ld
lines.
9 .1 Magnetic fields
Magnetic fields interacting
You probably already know about the forces between two magnets.
•
Two north poles repel.
•
Two south poles repel.
•
A north and a south pole attract.
This force is due to the magnetic fields from each magnet.
Look at the field lines between two magnets when their
opposite poles are together.
The magnetic field lines between the two magnets are all
pointing in the same direction. This means there will be a force of
attraction between the magnets.
Now look at the field lines between two magnets
when their like poles are together.
The magnetic field lines in the space directly between
these two magnets are all pointing in opposite
directions. This means the magnets will repel, or try
to move away from each other.
Questions
1
Describe what is meant by the term ' magnetic field'.
2
The magnetic field of magnet A extends further than the
magnetic field of magnet B.
State what can be concluded about the strengths of these
two magnets.
3
Copy this diagram of a bar magnet.
Draw the magnetic field lines around your diagram.
s
N
Draw a total of eight lines and put arrows on each line.
4
a
Draw magnetic field lines to show how a north and a
south pole attract.
b Draw magnetic field lines to show how two south poles repel.
295 )
_ _ _ _ _ _9__
M_a_g_n_e_t_
is_m_ _ _ _ _ _ _ _ _ _ ___,)
Activity 9. 1.1
Showing a magnetic field pattern
Work in pairs.
You will need :
• a bar magnet • a horseshoe magnet (optional) • a piece of A4 size paper
• piece of thick card, up to, but not thicker than, the thickness of the magnet
• iron filings
Safety
Be careful not to get the iron fi lings on your skin. They can be sharp and get stuck
in your skin.
Be careful not to get the iron fi ling on the magnet. They are very difficult to remove
and other people will get the iron filings on their skin.
Method
1
Cut a hole in the middle of the thick card, just
large enough to put the bar magnet in.
2
Put the bar magnet into the hole so it lies flat
in the card . The card is to support the paper
and keep the paper level.
3
Put the paper on top of the card so the
magnet is under the middle of the paper.
4
Gently and evenly sprinkle the iron filings
over the paper. Tap the paper gently to allow
the iron filings to move into position.
You should see a pattern like the one in the picture.
Questions
1
2
a Where is the magnetic fie ld strongest?
b How can you tell this from the pattern of iron fi lings?
a Can you tell by looking at the pattern of iron filings, which is the north or
south pole?
b Explain your answer.
3
Look close ly at the iron filings that are on top of the poles of the magnet.
What do you observe?
When you have finished, carefully lift the paper vertica lly away from the magnet.
Bend the paper to form a slight 'U' shape and use this as a channel to pour the
iron filings back into the container.
296)
9.1 Magnetic fields
Continued
Extension
If you have time, you could use two magnets, first arranged with like poles
facing and then with opposite poles facing. In each case, try to explain the
pattern of iron filings.
Think like a scientist
Detecting a magnetic field
In this investigation, you will investigate ways of detecting a magnetic field.
Work in pairs or groups of three.
You will need:
See the diagram. You could also choose some other different types of magnets
to investigate.
u
Method
1
Set the magnet, ruler and paperclip on the smooth surface as shown in the d iagram.
bar magnet
ruler
paperclip
WlllllllilllllllJl2liwlllJil3llliillill4llliJ!lluslilllllll6
1illillJLLlill
7 llllli.lillsllillWJ
9 llllllilil1
ollllllilll11JlllilWl1
2JlllilllJ
13llllllllil
14= ,U
smooth surface
2
Record whether the north or south pole of the magnet is facing the paperclip.
3
Slowly move the paperclip toward the pole of the magnet.
4
Record the distance from the pole of the magnet when the paperclip becomes attracted
to the magnet. Call this value d for distance.
5
Repeat another two times and record all your measurements of d.
6
Turn the magnet around so the other pole is facing the paperclip.
7
Repeat steps 3-5 for this pole.
8
If you have t ime, repeat the investigation with other, different, magnets.
Continued
297 )
_ _ _ _ _ _9__
M_a_g_n_e_t_is_m_ _ _ _ _ _ _ _ _ _ ___,)
Continued
Questions
1
Calculate the average of your
2
Explain how the value of
3
Explain what your results show about the strength of the magnetic field from
the north and south poles of the same magnet.
4
Explain why:
5
va lues for each pole of each magnet you tested.
is related to the strength of the magnetic field.
a
the surface needs to be as smooth as possible
b
the paperclip needs to be as small as possible.
Suggest how you cou ld improve this investigation to get more accurate values of d.
Self-assessment
For each of these statements, decide on how well you agree. Give yourself 5 if you
agree very much and 1 if you do not agree at all.
•
I understand what is meant by a magnetic field.
•
I can draw the magnetic field lines around a bar magnet.
•
I can draw the magnetic field lines between two opposite poles of different
bar magnets.
•
I can draw the magnetic field lines between two like poles of different bar magnets.
Summary checklist
I can describe what is meant by the term magnetic field.
I can explain how to detect a magnetic field.
I can draw magnetic field lines around a magnet.
I can draw magnetic field lines between two magnets.
(U
9.2 The Earth as a giant magnet
> 9 .2 The Earth as a giant magnet
In this t o pic you wil l:
•
discover that the Earth has a magnetic field
•
learn that the core of the Earth acts as a magnet
Getting started
Work in groups to discuss the answers to these questions.
•
•
Where are the terms 'north pole' and 'south pole' used,
in addition to their use with magnets?
What is a magnetic compass used for, apart from science
experiments in school?
geographic north
pole
magnetic north
naturally
occurring
navigate
______
9_M_
a_g_n_
et_i_sm
_ _ _ _ _ _ _ _ _ _ _ _ _)
The Earth's magnetic field
Around 4000 years ago, a Greek shepherd called Magnes was looking after
his sheep. The story of Magnes says that iron nails in his shoes stuck to
one particular type of rock. The rock was called lodestone and contained
a substance that was later named magnetite, which is a naturaHy occurring
magnet. 'Naturally occurring' means it is not made by people.
Both the Greeks and the Chinese started to investigate magnetic properties.
The Chinese discovered that a small needle of lodestone,
split off the rock, could be made to float on water. When
allowed to float, the needle of lodestone always turned to
point in the same direction.
One end of the needle pointed toward the north and the
other end pointed toward the south. This was the invention
of the magnetic compass.
It was soon discovered that the compass needle pointed to
a position close to the Earth's north pole, but not exactly
to the geographic north pole. This point is now called
magnetic north. Magnetic north moves very slowly, and is
currently in the Arctic Ocean, north of Alaska.
The first compasses, in 200 BCE, looked like this.
The invention of the compass was very important because
it allowed people to nm,igatc in places such as oceans and
deserts, with less chance of getting lost. With a compass,
you will always know what direction you are facing.
Even today with satellite navigation (satnav), ships and
aeroplanes still use magnetic compasses.
Satellite navigation, or satnav, systems do not use the
Earth's magnetic field.
Some animals, such as the birds in the photograph, use
the Earth's magnetic field to navigate over long distances.
Figure 9.2.2 shows what the Earth's magnetic field lines
look like compared with a bar magnet.
The compass on this mode rn ship is the bowlshap ed o bject near the centre of the p icture.
....
These birds are using the Earth's magnetic fie ld to navigate.
300)
The Earth's magnetic field is similar to that of a bar magnet .
9.2 The Earth as a giant magnet
Notice, in the diagram, that the magnetic field lines around the Earth
point towards the Earth's north pole. You will remember from Topic 9.1
that magnetic field lines point from north to south.
This means that the north pole of Earth is actually a magnetic south pole!
The term magnetic north, when used in context of the Earth and navigation
means the magnetic pole that is close to the geographic north pole.
In the same way, magnetic south is the magnetic pole that is close to the
geographic south pole.
The geographic north and south poles are the parts of the Earth
through which the spin axis passes.
The Earth's magnetic field causes the natural appearance of lights visible
in the night sky close to the north and south poles. These are caused by
particles coming from the Sun arriving into the stronger parts of the
Earth's magnetic field.
0
The needle on this magnetic compass is pointing
towards the Earth's magnetic north.
This natural light display is caused by the Earth's magnetic fi eld.
Origin of the Earth's magnetic field
People once thought that the Earth was made almost entirely from
magnetic rocks. However, it is now known that the high temperatures deep
inside the Earth would cause rocks to lose any magnetism that they had.
Scientists also know that the Earth's magnetic field has reversed in the
past. The last change was around 500 000 years ago, when south really
was north!
301 )
______
9_M_a_g_n_et_i_sm
_ _ _ _ _ _ _ _ _ _ _ _ _)
It is now known that the Earth's core is the origin of the magnetic field,
but scientists have still to discover the exact reason for this. They think
the heat generated in the core, which is mostly made from iron, causes it
to continually create a magnetic field. The core also contains some nickel,
which is another magnetic metal. The movement in the liquid outer core
would explain why the magnetic poles move slowly, and have occasionally
reversed. Magnetic north moves at a speed of about 60 km per year.
Airport runways are numbered according to their direction from magnetic north. The numb ers sometimes have to be changed
due t o movement of magnetic north.
Questions
1
Name the piece of equipment that is
used for navigation and uses the Earth's
magnetic field.
2
A bar magnet is allowed to rotate freely. Explain which pole of the
bar magnet will point to geographic north.
3
The position of magnetic north on Earth moves at a speed of about
per year. Explain why the position of magnetic north can still be
used for navigation on a 12-hour journey.
4
a
What part of the Earth's structure causes the Earth's magnetic field?
b
Name the magnetic metal that makes up most of this part.
a
Draw a circle to represent the Earth. With the top of your circle
representing geographic north, draw the magnetic field lines
around the Earth. Add arrows to show the direction of the field.
5
b State the relationship between the direction of the magnetic field
lines and the direction that a magnetic compass will point.
302)
9.2 The Earth as a giant magnet
Think like a scientist
Detecting the Earth's magnetic field
In this activity, you will change variables and describe how observations change.
Work in groups of two or three.
You will need:
• a needle or thin iron nail
• paper and scissors
• a bar magnet
• adhesive tape
• light string or thread
• a bowl of water
• a wooden clamp stand or non-magnetic support
• a piece of cork or polystyrene on which the needle or nail will float
Method: Part 1
1
Make a paper support for the bar magnet so that the magnet will
hang horizontally, as shown in the diagram.
2
Use the light string to hang the magnet, in the paper support, from
the wooden clamp stand as shown in the picture. Make sure there
are no other magnets or large magnetic objects close by.
3
Allow the magnet to come to rest. Record the direction the magnet
is pointing.
4
Move the equipment to another part of the room . Again record the
direction the magnet is pointing.
Method: Part 2
5
Hold the needle or nail and gently stroke the bar magnet
along it several times. as shown in the diagram.
6
Record:
•
which pole of the magnet was in contact with the needle
•
which d irection the magnet moved along the needle.
7
Move the magnet away from where you are working.
8
Cut a disc from the cork or a circle from the polystyrene. Set
the needle on the disc and float the disc in the water, in a
non-magnetic dish as shown.
9
As in Method: Part 1, make sure there are no other magnets or
large magnetic objects close by.
----------
. ....
....
10 Allow the needle to come to rest and record the direction it is pointing.
11 Carefully move the equipment to another part of the room and record
the direction the needle is pointing.
303)
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9_M_ag_n_e_t_is_m_ _ _ _ _ _ _ _ _ _ __,)
Continued
Questions
1
In Method: Part 1 and Method Part 2, the investigation is carried out in two
different parts of the room. Explain the reason for this.
2
a
In Method: Part 1, which pole of the magnet pointed north?
b Explain what this shows about the poles of the Earth's magnetic field.
3
4
a
In Method: Part 2, state which end of the needle pointed north.
b
Use your answers to 2 to help you to state which pole of the magnetised
needle was pointing north.
a
Which pole of the magnet was used to stroke the needle or nail?
b Which end of the needle was the magnet removed from after each
stroking action?
c
5
What is the relationship between your answers to 4a and 46?
In Method: Part 1 and Method Part 2, you made magnetic compasses.
Explain why these compasses wou ld not be practical for navigation
on a j ourney.
Self-assessment
Answer 'yes' or 'no' to each of these questions.
•
I understand that the Earth has a magnetic field.
•
I can explain why the north pole of a magnetic compass points north,
even though like poles repel.
•
I can describe an experiment to show that the Earth has a magnetic field.
Summary checklist
D I know that the Earth has a magnetic field.
D I can draw a diagram to show the Earth's magnetic field lines.
D I can understand why the north pole of a freely rotating magnet points north.
D I know that the core of the Earth is the origin of the Earth's magnetic field.
304)
-
:.;::;
9.3 Electromagnets
> 9 .3 Electromagnets
In this topic you wil l:
•
describe how to make an electromagnet
•
recall some applications of electromagnets
Getting started
Key words
Work in groups to consider applications where it would be useful
to have a magnet that could be switched on and off.
coil
core
electromagnet
magnetic
magnetised
permanent
magnets
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M_a_g_n_e_t_
is_m_ _ _ _ _ _ _ _ _ _ ___,)
Properties of magnetic materials
A material is described as magnetic if it is attracted to a magnet.
Magnetic materials include the metals iron, nickel and cobalt. Steel
is another common magnetic metal. Steel is a mixture that contains
a large proportion of iron.
Magnetic materials can be magnetised. Magnetised means turned into
a magnet. The magnets you have used were all made by magnetising
magnetic materials.
The magnets you have used are called permanent magnets because
they have a magnetic field that is always there. You cannot switch the
magnetic field off and on again.
One way to magnetise a magnetic material is by using electricity.
When this method is used, the magnet is called an electromagnet.
Electromagnets
An electromagnet is made by wrapping a wire around a
magnetic material, such as iron. The wire that is wrapped
around is a called a coil. The material in the middle of the
coil is called the core.
When current passes through the coil, the magnetic material
becomes magnetised.
When the current is switched off, the magnetic material loses
most of its magnetism.
The diagram shows the simplest type of electromagnet.
Poles of an electromagnet
An electromagnet has two poles, similar to a bar magnet.
You can find out which pole is which in two simple ways.
•
•
Use a magnetic compass. A magnetic compass points along
magnetic field lines, so will point towards the south pole.
Use a bar magnet with known poles. Opposite poles attract
and like poles repel so, by bringing the bar magnet close to the
electromagnet, you can detect which pole is which.
You can reverse the poles of an electromagnet in one of two ways.
•
Wrap the coil around in the opposite direction.
•
Reverse the connections on the cell or power supply.
Applications of electromagnets
Electromagnets are used in many applications where a permanent
magnet would not be useful.
306)
iron nail
coiled wire
cell
>---
wire
9.3 Electromagnets
The :fire door in the picture is held open with an electromagnet.
The electromagnet is connected to the fire alarm. When the
fire alarm is switched on, the magnet is switched off and the
door closes.
When t he electromagnet on the wall is
switched off, the door will close.
Some types of scanners in hospitals use powerful electromagnets.
An MRI scanner is used to produce images from inside the
human body. MRI stands for magnetic resonance imaging.
This MRI scanner uses a powerful
electromagnet.
Electromagnets can also be used for sorting scrap metal. The
electromagnet will attract iron and steel, leaving other nonmagnetic metals behind. Common non-magnetic metals include
copper, aluminium and zinc. When the magnetic metals have
been lifted, they can be moved away and then dropped by
switching off the magnet.
This electromagnet is sorting through scrap
metal at scrapyard.
In a toaster, when the handle is pushed down, an electromagnet
holds a metal basket down. A timer turns the electromagnet off
and the metal basket then pops up containing the toast.
When t he electromagnet in the toaster
switches off, the toast pops up.
An electric bell uses an electromagnet to make the hammer move.
When the electromagnet is on, the hammer is pulled onto the
bell. The movement breaks the circuit and the hammer moves
away from the bell. The circuit becomes complete again and the
hammer is pulled back to the bell. This continues until the power
supply is turned off. Electric bells are used in schools, as fire
alarms and as door bells.
The cover has been removed to show the
electromagnet inside t his electric bell. There
are two coils of wire in this electromagnet.
Electric motors use electromagnets to change electrical energy
into kinetic energy.
This is the electromagnet from inside a small
electric motor.
307 )
_ _ _ _ _ _9__
M_a_g_n_e_t_is_m_ _ _ _ _ _ _ _ _ _ ___,)
Questions
1
Which of h, 0 of these metals can be magnetised?
1
copper
iron
aluminium
steel
silver
t in
2 Explain the difference between 'magnetic' and 'magnetised'.
3
State the main difference between an electromagnet and a
permanent magnet.
4
Draw a diagram to show how an electromagnet could be made from:
•
a cell
•
•
a switch
a coil of wire
•
an iron nail.
Use circuit symbols for the cell and the switch.
5
a
List three applications of electromagnets.
b For one of your applications, explain why a permanent magnet
would not be suitable.
308 )
9.3 Electromagnets
Activity 9.3.1
Making an electromagnet
Work in groups of two or three.
You will need:
• a cell
• a cell holder or adhesive tape
• about 1 m of plastic-coated wire with about 1 cm of insulation removed at each end
• leads for use in circuits
• a switch
• a large iron nail
• paperclips
Method
6
Wrap the insulated wire around the iron nail to form a coil, as
shown in the picture. Wrap the turns tightly around the nail and
use as much of the length of the nail as you can.
Leave enough wire at each end to connect to the cell. Make sure
only the plastic coating of the wire is in contact with the nail.
7
Connect the coil into a circuit as shown in the diagram.
8
Test your electromagnet to see if the end of the
nail will pick up paperclips. Use the pointed end
of the nail.
Only switch on your electromagnet for the
shortest possible time, otherwise the ce ll wi ll
not last long.
iron nail
coil of
insulated wire
Questions
1
Suggest why it is important that only the p lastic coating of the
wire makes contact with the nail.
2
In this activity, the whole length of the nail becomes magnetised.
Suggest why you test the electromagnet by attaching paperclips
to the end of the nail and not the middle of the nail.
3
a
Describe how you could find out whether the pointed end of
the nail was the north pole or south pole of the electromagnet.
b
State what wou ld happen to this pole if the cell in the circuit
were reversed so current flowed in the opposite direction.
Self-assessment
Answer these questions after completing the activity.
•
Could you make an electromagnet by yourse lf?
•
If not, what would you need help with?
309)
_ _ _ _ _ _9__
M_a_g_n_e_t_is_m
______________)
Summary checklist
D I can understand the difference between an electromagnet and a permanent magnet.
D I know how to make an electromagnet.
D I know some applications of electromagnets.
9.4 Investigating electromagnets
>9.4 Investigating electromagnets
In this topic you wil l:
•
discover which factors (or variables) affect the strength of an
electromagnet
•
investigate how these variables affect the strength of an
electromagnet
Getting started
Key words
Work in groups to discuss these questions.
factors
What are some differences between the e lectromagnets used for
soft iron
•
sorting scrap metal and for working a toaster
•
keeping a fire door open and for working an electric bell
311)
_ _ _ _ _ _9__
M_a_g_n_e_t_is_m
_ _ _ _ _ _ _ _ _ _ _ ___,)
Strength of electromagnets
Topic 9.3 listed the three things that are needed to make an electromagnet:
•
•
•
a coil of wire
a magnetic core inside the coil
an electric current flowing in the coil.
These three things are the factors that will affect the strength of an
electromagnet.
•
•
•
The number of turns in the coil. The more turns in the coil, the
stronger the electromagnet.
The material of the core. Iron and some types of steel in the core
make the strongest electromagnets.
The current in the coil. The greater the current, the stronger the
electromagnet.
A factor is another word for a variable that will affect something.
The diagrams show the three ways to increase the strength of an
electromagnet.
Increase the number of
turns on the coil.
1
Increase the number of turns on the coil. Keep the current and core the same.
15 turns of wire
Use more cells to
increase the current.
2
20 turns of wire
Increase the current. Keep the number of turns on the coil and the core t he same.
r-----------4
15 turns of wire
Use a soft iron core in
place of a steel core.
3
-------.
15 turns of wire
Change the core to soft iron. Keep the number of turns on the coil and the current the same.
15 turns of wire
312 )
~
15 turns of wire
9.4 Investigating electromagnets
Soft iron is not soft in the same way as modelling clay is soft. Soft
iron is the term used for iron that is easily magnetised and also easily
demagnetised. Demagnetised means it has lost its magnetism.
In 2019, scientists broke the world record for the strongest electromagnet.
They made an electromagnet 4500 times stronger than a school bar
magnet. It uses more electricity than three million electric lamps!
The strength of an electromagnet can be measured by the force that the
electromagnet exerts on a magnetic material. The easiest way to do this is
to see how many magnetic objects that the electromagnet can lift and hold.
Questions
1
Explain why an electromagnet for sorting scrap metal needs to
be stronger than the electromagnet that holds the handle of a
toaster down.
2
State the three factors that affect the strength of an electromagnet.
3
The diagrams show circuit diagrams for four electromagnets.
Each has the same current and the same number of turns in the
coils. The material of the core is shown on each diagram.
rubber
wood
A
B
nickel
aluminium
C
D
Which of the circuit diagrams will make the strongest electromagnet?
Write one letter.
4
A science laboratory called CERN in Switzerland uses many very
strong electromagnets. The electricity used by CERN is the same as
that of a small city. Suggest why CERN uses so much electricity.
313 )
______
9_M_ag_n_e_t_is_m_ _ _ _ _ _ _ _ _ _ __,)
Think like a scientist
Investigating electromagnet strength
In this activity, you will carry out investigations and plan further investigations
on the strength of electromagnets.
Work in groups of two or three.
You will need:
• three 1.5 V cells or an adjustable d.c. power supply with safety cut-out
• leads and connectors
• switch
• an ammeter
• iron nail
• paperclips of different sizes
• plastic-coated wire at least 1 m long with about 1 cm of plastic removed from
each end
• selection of similar-sized cores to the iron nail, such as a wooden pencil,
roll of paper, plastic pen and at least one other metal
Safety
u
Only keep you r electromagnet switched on for the shortest possible time,
otherwise your cel ls wi ll not last long.
0
Check that the wire in the coil is not becoming hot. If the wire becomes hot,
switch off immediately and tell your teacher.
Method: Part 1 - changing the number of turns in the coil
1
Make an electromagnet. Use the number of ce lls or the power supply
setting that your teacher advises. (You should recall how to make an
electromagnet from Topic 9.3.)
C
Use the iron nail for the core.
Wrap the wire around the core to make five turns.
2
Switch on the electromagnet and see how many paperclips it will hold.
Record this resu lt.
3
Switch the electromagnet off and increase the number of turns on the
coil by five.
4
Switch on the electromagnet and see how many paperclips it will hold.
Record this resu lt.
5
Repeat steps 3-4 until you can't fit any more turns on the core.
6
Repeat the entire investigation. If any of your results are different, you may
need to repeat them a third time.
314 )
E
0
9.4 Investigating electromagnets
Continued
Questions
1
Record your results in a table.
2
Calculate the average number of paperclips for each number of turns
in the coil.
3
Draw a line graph of your results. Put number of turns in the coil on the
horizontal axis.
4
Describe the trend in your results.
Method: Part 2 - changing material in the core
1
Make an electromagnet. Use the iron nail as the core. Wrap the maximum
number of turns in the coil that will fit on the core. Use the number of cel ls
or the power supply setting that your teacher advises.
2
Switch on the electromagnet and see how many paperclips it will hold.
3
Repeat this with other core materials. The other cores should be about the
same diameter, so you should not have to unwind the coi l each time.
4
As in Method: Part 1, repeat each of your measurements.
Que stions
5
Record your results in a table.
6
For each core material, calculate the average number of paperclips
for each number of turns in the coil.
7
Draw a bar chart of your results. Put the materials of the core on the
horizontal axis.
8
Describe any trends in your resu lts.
9
Explain why a line graph was used in Part 1 and why a line graph
would not be suitab le in Part 2.
Method Part 3 - changing the current in the coil
In this part, you wi ll plan the investigation yourself.
The aim of this part is to investigate how the current in the coil affects the
strength of the electromagnet.
1
Decide which variable to change and how you wi ll change it. Your teacher can help
with this.
2
Decide which variables you will control.
3
Draw a circuit diagram for your electromagnet.
4
Make a prediction for your investigation.
5
Decide whether large or small paperclips will give better results.
Explain your choice.
Continued
315 )
_ _ _ _ _ _9__
M_a_g_n_e_t_is_m_ _ _ _ _ _ _ _ _ _ ___,)
Continued
6
If you have time, carry out your investigation and record your resu lts in
a suitable table.
Questions
10 Explain whether a line graph or a bar chart is more suitable to display
your results.
11 Display your resu lts in the type of graph you have chosen.
12 Explain whether your prediction was accurate.
Self-assessment
Rate your confidence in each of these statements.
•
I can recall the three factors that affect electromagnet strength.
•
I could plan an investigation to test the effect of changing one of
these factors.
•
I can understand whether a line graph or bar chart is more suitable
for presenting results.
Summary checklist
D I can recall the factors that affect the strength of an electromagnet.
D I can predict how a change in any one of these factors will affect the strength
of the electromagnet.
(U
Check your progress
9 .1 What is a magnetic field?
Write one letter.
[1]
A
An area where you can use a magnet.
B
An area where magnetism can be detected.
C
An area to store magnets.
D
An area where all magnets are not allowed.
[1]
9 .2 What direction do magnetic field lines point?
5 ➔ N
9 .3 a
N ➔ N
Copy the diagram of a horseshoe magnet.
N
s
Draw the magnetic field pattern of the horseshoe magnet on
your diagram.
b
Copy the diagram of two south poles from different magnets.
s
s
Draw the magnetic field pattern between these two south poles
on your diagram.
9
Magnetism
9 .4 Copy this diagram of the Earth on its axis.
N
s
The letters N and S on the diagram show the geographic poles.
Draw the pattern of the Earth's magnetic field on your diagram.
[3]
9 .5 A soft iron cylinder produces no change in the reading of a magnetic compass.
A coil of wire is wrapped around the soft iron cylinder. Electric current is
passed through the coil.
What change happens in the soft iron cylinder?
Write one letter.
A
It starts to become magnetic.
B
It starts to become a permanent magnet.
C
It starts to become magnetised.
D
It starts to become demagnetised.
9 .6 a
b
[11
State the name given to a magnet that can be switched on and off.
[1]
Draw a labelled diagram to show how this type of magnet could be made.
[4]
9 .7 Arnn makes an electromagnet using:
•
one l.5 V cell
•
an iron nail 15cm in length
•
10 turns of wire around the nail.
a
State the effect on the strength of this electromagnet if Arnn increases
the number of turns of wire around the nail to 20.
[11
b
Arun uses an ammeter to measure the current in the electromagnet circuit.
Arnn then varies the current. For each current, Arun measures the number
of paperclips that the electromagnet will hold.
State the independent variable in this investigation.
[11
ii
State the dependent variable in this investigation.
[11
iii
Copy these graph axes and sketch the shape of graph you would
predict for the results.
[2]
Assume both axes start at zero.
Number of
paperclips held
Current in electromagnet
c
Arnn wants to investigate the effect of changing the material in the core
of her electromagnet.
List two factors that Arun will need to keep constant when changing
the material in the core.
ii
Which of these materials in the core will make the strongest
electromagnet?
Choose one material.
paper
copper
plastic
cobalt
_ _ _ _ _ _9__
M_a_g_n_e_t_is_m_ _ _ _ _ _ _ _ _ _ ___,)
Project: Investigating magnetism
Background
Magnetism is all around us in our daily lives. Fridge magnets, computer hard
disc drives, electric motors and headphones all use magnetism.
Topic 9.2 gave some information about the discovery of magnetism, and a little
information about how some animals use the Earth's magnetic field.
Your task
Work in groups of three or four.
Your group can find out about some of these different aspects of magnetism:
•
more about the early discoveries in magnetism
•
more about how animals use magnetism
•
how the Earth's magnetic field protects us
•
magnetic fields around other planets in the Solar System
•
the strongest known natural magnets in the universe
•
the many and varied uses of magnets
You do not have to include all of these, or you could find out about other aspects
of magnetism.
Connect the information you find to tell a story.
Present this story in any way you choose, for example:
•
a picture story board
•
•
a poem
•
a song.
a stage play
A ll members of the group should have a role in presenting the story.