THE WESTMINSTER SCHOOL, DUBAI
1
INDEX
UNIT
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
3
3.1
3.2
3.3
3.4
3.5
3.6
TOPIC
MEASUREMENTS
Introduction to measurements
Number and units
System of units
Measuring length
Measuring time
Measuring mass
Measuring volume
Measuring density
Scalars and vectors
ELECTRICITY
Electric charge
Charging
Earthing and induced charges
Electric field
Conductors and insulators
EARTH AND SPACE
Structure of the Earth
Tectonic plates
Earthquakes
The solar system
Living in space
The life cycle of a star
2
PAGE NO.
3
4-6
7-9
10-15
16-19
20-22
23-25
26-30
31-36
37-43
44
45-47
48-50
51-54
55-58
59-61
62
63-66
67-71
72-78
79-88
89-98
99-105
UNIT 1
MEASUREMENTS
3
1.1
Introduction to Measurements
Introduction to Units and Measurements
Physics explains the law of nature in a special way. This explanation includes a
quantitative description, comparison, and measurement of certain physical
quantities.
The range of objects and phenomena studied in physics is immense. From the
incredibly short lifetime of a nucleus to the age of the Earth, from the tiny sizes
of sub-nuclear particles to the vast distance to the edges of the known universe,
from the force exerted by a jumping flea to the force between Earth and the Sun.
Figure 1.1 Size of the sub nuclear particles
Figure 1.2 The distance from Earth to the Moon
may seem immense, but it is just a tiny fraction
of the distances from Earth to other celestial
bodies. (credit: NASA)
A physical quantity is a property of a material or system that can
be quantified by measurement. A physical quantity can be expressed as the
combination of a numerical value and a unit.
To measure or compare a physical quantity we need to fix some standard unit of
the quantity. The weight of lion is heavier than a goat. But how many times? Robin
is taller than Mark, but how tall? To answer such questions we need to fix some
unit. Suppose mass is the unit, then we can conclude that weight of the lion is 200
times to that of a goat. Similarly, if we use length as a unit, we can easily
determine that Robin is 2 times unit taller to that of Prashant. Thus the physical
quantities are described in terms of a unit of that quantity.
There are a large number of physical quantities to measure and they are classified
basically into two categories: Fundamental and Derived Quantities.
4
Fundamental Quantities:
The quantities that do not depend on other physical quantities of measurement
are called Fundamental Quantities. They are also known as Base Quantities. The
units determined for fundamental quantities are called Fundamental Units.
Quantity
Unit
Symbol
Mass
Kilogram
kg
Time
Second
s
Temperature
Kelvin
K
Electric Current
Ampere
A
Luminous Intensity
Candela
cd
Length
Meter
m
Amount of
Substance
Mole
mol
Derived Quantities:
There are only 7 fundamental quantities, rest physical quantities are known
as Derived Quantities. The physical quantities that depend on other quantities
for their measurements are called Derived Quantities. They are many in number
and are obtained by mathematical calculations of fundamental quantities. The
units that determine derived quantities are called Derived Units.
Few examples:
Quantity
Unit
Symbol
Acceleration
Meter/second2
m/s2
Area
Meter2
m2
Volume
Meter3
m3
Velocity
Meter/second
m/s
Force
Kilogram-meter
second2
N
(newton)
Density
Kilogram/meter3
Kg/m3
5
Exercise:
1. Fill in the S.I. units for the following quantities:
Quantity
Unit
Symbol
Length
Mass
Time
Temperature
Force
Density
2. Complete the table below on the measurement of come common physical
quantities using some laboratory instruments.
3. The diagram below shows a rectangle.
Use your ruler to measure the length and breadth of the rectangle.
Record your reading in centimetres (cm) below.
Length = _______________ Breadth = _______________
6
1.2 Numbers and units
When you make a measurement, you might get a result like the one above: a
distance of 12 m. The complete measurement is called a physical quantity. It is
made up of two parts: a number and a unit.
12 m really means 12 x m (twelve times metre), just as in algebra, 12x means 12
X x (twelve times x). You can treat the m just like a symbol in an algebraic
equation. This is important when combining units.
Combining units
In the diagram above, the girl cycles 10 metres in 2 s. So she travels 5 metres
every second. Her speed is 5 metres per second. To work out the speed, you
divide the distance travelled by the time taken, like this:
speed=
10 𝑚
2𝑠
(s is the symbol for second)
As m and s can be treated as algebraic symbols:
speed =
10 𝑚
2
.
𝑠
To save space, 5
=5
𝑚
𝑠
𝑚
𝑠
is usually written as 5m/s.
So m/s is the unit of speed.
Rights and wrongs
This equation is correct: speed=
10 𝑚
2𝑠
=5 m/s
7
Advanced units
1/s can also be written
as s-1. So the speed can
be written as 4 m s-1.
This method of
showing units is more
common in advanced
work.
This equation is incorrect: speed=
10
2
= 5 m/s
It is incorrect because the m and s have been left out. 10 divided by 2 equals 5
and not 5 m/s.
Strictly speaking, units should be included at all stages of a calculation, not just at
the end. However, in this book, the 'incorrect' type of equation will sometimes be
used so that you can follow the arithmetic without units which make the
calculation look more complicated.
Bigger and smaller
You can make a unit bigger or smaller by putting an extra symbol. called a prefix,
in front. (Below, W stands for watt, a unit of power.)
Prefix
Symbol
Scientific
notation
Value
Example
giga
G
109
1 000 000 000
9 GW (gigawatt)
mega
M
106
1 000 000
5 MW (megawatt)
kilo
k
103
1 000
53 km (kilometre)
Base unit
100
1
12 m (metre)
deci
d
10-1
1/10 or 0.1
8 dm (decimetre)
centi
c
10-2
1/100 or 0.01
15 cm (centimetre)
milli
m
10-3
1/1000 or 0.001
0.5 mg (milligram)
micro
µ
10-6
nano
n
10-9
1/1 000 000 or
0.000001
1/1 000 000 000 or
0.000000001
60 µA
(microampere)
72.5 ns
(nanosecond)
Scientific notation
An atlas says that the population of Iceland is this: 320000
There are two problems with giving the number in this form. Writing lots of zeros
isn't very convenient. Also, you don't know which zeros are accurate. Most are
only there to show you that it is a six-figure number.
8
These problems are avoided if the number is written using powers of ten:
3.2 x 105 (105 = 10 x 10 x 10 x 10 x 10 = 100000)
‘3.2X 105’ tells you that the figures 3 and 2 are important. The number is being
given to two significant figures. If the population were known more accurately,
to three significant figures, it might be written like this:
3.20 x 105
Numbers written using powers of ten are in scientific notation or standard
form. The examples on the right are to one significant figure.
Exercise:
1. How many grams are there in 1 kilogram?
2. How many millimetres are there in 1 metre?
3. How many microseconds are there in 1 second?
4. This equation is used to work out the area of a rectangle: area= length X width.
If a rectangle measures 3 m by 2 m, calculate its area, and include the units in
your calculation.
5. Write down the following in km:
2000 m
200 m
2 x 104 m
6. Write down the following in s:
5000 ms
5 x 107 µs
7. Using scientific notation, write down the following to two significant figures:
1500 m
1500 000 m
0.15 m
0.015m
9
1.3 System of units
Unit
To measure any quantity or compar
acquired standard called Unit. The
expressed in terms of a number/qu
Measurement = Quantity × Unit
Example:
 John studies for 3 hours, then “3” is the number or quantity and “hour” is the
unit of time.
 Sam weighs 81 kilograms or kg then “81” is the number or quantity and “kg” is
the unit of weight.
 Steve is 20 cm taller than Jane, here “20” presents number or quantity and
“cm” represents unit of length.
Need for a system of units
Every quantity in physical world requires a unit to explain or define it. It is because
of units only; the physical world is classified so well. Imagine what the condition
of Earth would be if there is no unit. To be precise, we won’t be able to calculate
things which will deteriorate the business markets. Adding further we won’t be
able to define quantities, which would end up creating a lot of daily problems to
all of us. To avoid so many confusions and problems physicist defined unit.
10
The System of Unit is defined as a set of units involved in arithmetic operations
of various physical quantities with the help of conversion factors. It further helps
in conveying information from one region to another in terms of units which
makes business and relations much easier.
Example: A farmer supplies food grain in America, through a transportation
system. The weight of 1 sack of grain is around 60 kg and there are around 1000
sacks. How much money will the farmer get from America, if the rate of food grain
in America is 4$ per pound?
Solution: The problem is simple. The physical quantity involved here is weight. In
UAE, the standard unit of weight is kilograms so the total weight of sacks will be
60,000 kilograms. In America, the unit of weight is pound so we will convert
kilograms into pounds and calculate the overall rate of food grain as the cost of
1000 pounds grain is 4$.
1 kilogram = 2.20 pounds
Then the weight of 60,000 kg in pounds will be = 2.20 × 60,000 = 1, 32,000 pounds
Cost of 1000 pounds food grain = 4$
Cost of 1, 32,000 pounds food grain will be = 4/1000 × 1, 32,000 = 528$
Thus, the total amount farmer will make will be 528 dollars.
How are units decided?
How do we choose a standard unit for a physical quantity? There are two points
to consider while choosing a unit.
 The unit should be internationally accepted; otherwise, everyone will come
with their own unit and create a hoax. This would abrupt communication
between two countries and end up degrading their economy. The right to
decide and mention unit is authorized by a body known as “General
Conference on Weight and Measures”. The organization held meetings and
addresses the changes in measurement through its publications.
 The unit should hold good with other international units.
Types of System of Units
There are three types of System of Units, which we put into use for physical world
to make measurements easier and reliable. The types of system of units are:



International System of Units or M.K.S
F.P.S system
C.G.S system
11
SI Units or International System of Units:
Most scientists use SI units (full name: Le Systeme International d'Unités). The
basic SI units for measuring mass, time, and length are the kilogram, the second,
and the metre. From these base units come a whole range of units for measuring
volume, speed, force, energy, and other quantities.
Other SI base units include the ampere (for measuring electric current) and the
kelvin (for measuring temperature).
Quantity
SI Unit
Symbol
Mass
kilogram
kg
Time
second
s
Temperature
Kelvin
K
Electric Current
Ampere
A
Luminous Intensity
Candela
cd
Length
metre
m
Amount of Substance
mole
mol
Units of Time, Length, and Mass: The Second, Meter, and Kilogram:
Length: The Metre
The SI unit for length is the metre (abbreviated m); its definition has also changed
over time to become more accurate and precise. The metre was first defined in
1791 as 1/10,000,000 of the distance from the equator to the North Pole. This
measurement was improved in 1889 by redefining the metre to be the distance
between two engraved lines on a platinum-iridium bar now kept near Paris.
In 1983, the metre was given its present definition as the distance light travels in
a vacuum in 1/299,792,458 of a second. This change defines the speed of light to
be exactly 299,792,458 metres per second. The length of the metre will change if
the speed of light is someday measured with greater accuracy.
12
Length
1 kilometre (km)
1 metre (m)
1 centimeter (cm)
1 millimetre (mm)
1 micrometre (µm)
1 nanometre (nm)
Comparison with base unit
Scientific notation
1000 m
103 m
1m
-
_1_ m
100
_1_ m
1000
___1____ m
1 000 000
_____1_____ m
1 000 000 000
10-2 m
10-3 m
10-6 m
10-9 m
Time: The Second
The SI unit for time, the second (abbreviated s), has a long history. For many years
it was defined as 1/86,400 of a mean solar day. More recently, a new standard
was adopted to gain greater accuracy and to define the second in terms of a nonvarying, or constant, physical phenomenon (because the solar day is getting
longer due to very gradual slowing of the Earth’s rotation). Cesium atoms can be
made to vibrate in a very steady way, and these vibrations can be readily observed
and counted. In 1967 the second was redefined as the time required for
9,192,631,770 of these vibrations.
Time
1 second (s)
1 millisecond (ms)
1 microsecond (µs)
1 nanosecond (ns)
Comparison with base unit
Scientific notation
1s
-
_1_ s
1000
___1___ s
1 000 000
_____1_____ s
1 000 000 000
10-3 s
10-6 s
10-9 s
Mass: The Kilogram
The SI unit for mass is the kilogram (abbreviated kg); it is defined to be the mass
of a platinum-iridium cylinder kept with the old meter standard at the
International Bureau of Weights and Measures near Paris. Exact replicas of the
standard kilogram are also kept at other locations around the world.
13
Mass
Comparison with base unit
Scientific notation
1000 kg
103 kg
1 kg
-
__1_ kg
1000
_1_ g & ___1____ kg
1000
1 000 000
10-3 kg
1 tonne (t)
1 kilogram (kg)
1 gram (g)
1 milligram (mg)
10-6 kg
Exercise:
1. What is the SI unit of length, mass & time?
2. What do the following symbols stand for?
g __________
mg __________
µm __________
t __________
ms __________
km __________
3. Write down the value of
a. 1364 mm in m
b. 2650 g in kg
c. 16 t in kg
d. 52 µs in s
e. 3.65 x 104 g in kg
f. 81.6 X 10-7 mm in m
4. The 500 pages of a book have a mass of 2.70 kg. What is the mass of each
page a) in kg b) in mg?
5.
km
s
µg
mg
µm
ns
t
g
nm
mm
kg
µs
m
ms
Arrange the units from the box in the columns as below. The units in each
column should be in order, with the largest at the top.
14
mass
length
time
6. For each of the following commonly used measurements, indicate its
symbol. Use the symbols to complete the following sentences with the
most appropriate unit. Units may be used more than once or not at all.
_____ millilitre
_____ milligram
_____ litre
_____ kilogram
_____ millimetre
_____ kilometre
_____ metre
_____ millisecond
_____ microgram
_____ centimetre
_____ gram
_____ second
a. Colas may be purchased in two or three _____ bottles.
b. The mass of a bowling ball is 7.25 _____.
c. The length of the common housefly is about 1 _____.
d. The mass of a paperclip is about 1 _____.
e. One teaspoon of cough syrup has a volume of 5 _____.
f. Stand with your arms raised out to your side. The distance from your
nose to your outstretched fingers is about 1 _____.
g. The body mass of a flea is about 0.5 _____.
h. On a statistical basis, smoking a single cigarette lowers your life
expectancy by 642,000 _____, or 10.7 minutes.
15
1.4 Measuring length
Length
Length is defined as the measurement or extent of something from one end to
the other end. We find it in almost every fundamental phenomenon in the
physical world.
All the external physical measurements rely on length. As an example, take your
height. How will you measure your height? What is your height? Height is simply
the distance between your feet and head. To measure the height you can use
either a scale or a measure stick. When using a ruler, be careful to
avoid parallax error.
The standard unit of Length is a metre, but being a small unit we refer to big units
to make measurements simple. Some examples of the unit are:



Height is measured in “foot” and “inches”, 1 feet contains 12 inches, and 1
inch means 0.0254 metres
Distance is measured in kilometres, 1 kilometre or km equals to 1000 metre.
While performing experiments in Physics lab we prefer small units like
millimetre and centimetre, 1 metre = 100 centimetres, and 1 centimetre = 10
millimetres.
Measurement of Length
We know some direct methods of measuring length using different kinds of
instruments. For example, we use centimeter scale to draw lines and measure the
length of small objects. When the nature of measuring objects change, we switch
to new instruments.
Some examples include:
 Lengths of several metres can be measured using a tape with a scale on it.
 With small objects, more accurate length measurements can be made using
the methods shown below.
16
1. Micrometer (below left): This has a revolving barrel with an extra scale on
it. The barrel is connected to a screw thread and, in the example shown,
each turn of the barrel closes (or opens) the gap by half a millimetre. First,
the gap is opened wide. Then it is closed up until the object being measured
just fits in it (a 'clicking' sound is heard). The diagram shows you how to take
the reading.
2. Vernier calipers (below right): This is an extra sliding scale fitted to some
length-measuring instruments. Its divisions are set slightly closer together
than normal so that one of them coincides with a division on the fixed scale.
The diagram shows you how to take the reading. (The vernier shown is part
of a set of calipers used for making external measurements. A second type
of caliper has jaws for making internal measurements.)
Zero error
You have to allow for this on many measuring instruments. For
example, bathroom scales might give a reading of 46.2 kg when
someone stands on them, but 0.1 kg when they step off and the
expected reading is zero. In this case, the zero error is 0.1 kg and the
corrected measurement is 46.1 kg.
To find the zero error on a micrometer or vernier calipers, you take a
reading when the gap is fully closed.
17
Exercise:
1. A student wants to find the thickness of one page of this book. Explain how
she might do this accurately.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
2. A micrometer is used to measure the diameter of a length of copper wire.
The zero error and scale reading are
as shown.
a. What is the zero error of the
micrometer?
_______________________________
b. What is the correct diameter of the wire?
_______________________________
3. Name two units of length which are bigger than a metre. How are they
related to the metre?
_______________________________________________________________
_______________________________________________________________
4. Five ball bearings are arranged by the side of the ruler, with two set squares
at either ends of the ball bearings.
The radius of one ball bearing is about.
A. 0.3 cm
B 1.8 cm
C 0.9 cm
18
D 3.3 cm
5. Rules that are 30 cm long are often made of wood or plastic that is thicker in
the middle, and thinner along the edges where the scale is printed. Explain why
the user is less likely to make an error if the rule is thinner at the edge, and
suggest reasons why the rule is thicker in the middle.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
6. Joko uses a plastic ruler to measure the length of the pencil, as shown in the
diagram below.
What is the length of the pencil?
A 2.1 cm
B 11.1 cm
C 2.2 cm
19
D 11.2 cm
1.5 Measuring time
Time
Time is defined as the period in which a process, action or an event takes
place. Time is an integral part of Physics and every single quantity in the physical
world relies on it. If time had not existed, there would be many irregularities in
schedule and timing of people. It is quite difficult to think of life when there is no
time.
Measurement of Time
To measure a time interval we need a clock. Modern clocks work on the atomic
standard of time, which is based on the periodic vibrations produced in a Cesium
atom. That’s why atomic clocks are also called Cesium Clock. The standard unit of
time is second.
Second is the universally accepted unit of time. 1 second is defined as the time
taken for 9,192,631,770 vibrations of the radiation relative to the transition
between two levels of ground state of Cesium-133 atom. The vibrations in atomic
or cesium clock are same as those in quartz clock which is mostly used in wrist
watches. The Cesium atomic clocks are very accurate and long lasting.
Time intervals of many seconds or minutes can be measured using a stopclock or
a stopwatch. Some instruments have an analogue display, with a needle ('hand')
moving round a circular scale. Others have a digital display, which shows a
20
number. There are buttons for starting the timing, stopping it, and resetting the
instrument to zero.
With a hand-operated stop clock or stopwatch, making accurate measurements
of short time intervals (a few seconds or less) can be difficult. This is because of
the time it takes you to react when you have to press the button. Fortunately, in
some experiments, there is an simple way of overcoming the problem. Here is an
example:
Simple Pendulum
A simple pendulum consists of a small mass like a metal bob suspended by a string
of negligible mass from a fixed support. A pendulum can be set up to investigate
the time taken for a single swing.
The pendulum above takes about two seconds to make one complete swing
Provided the swings are small, every swing takes the same time. This time is called
its period. You can find it accurately by measuring the time for 25 swings, and
then dividing the result by 25.
For example:
Time for 25 swings = 58 seconds
So: time for 1 swing = 58/25 seconds = 2.32 seconds
21
Exercise:
1. A student measures the time taken for 20 swings of a pendulum. He finds
that the time taken is 46 seconds,
a. What time does the pendulum take for one swing?
_______________________________________________________________
b. How could the student have found the time for one swing more accurately?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
2. A student tries to measure the period of a pendulum that is already swinging
left and right. At the moment when the pendulum is fully to the left, she
counts 'One' and starts a stopwatch. She counts successive swings each time
that the pendulum returns to the left. When she counts ‘Ten' she stops the
stopwatch, and sees that it reads 12.0 s.
a. What was her mistake?
______________________________________________________________
b. What is the period of swing of this pendulum?
______________________________________________________________
c. In this particular experiment, explain the likely effect of her reaction time
on her answer.
______________________________________________________________
______________________________________________________________
3. Group A and group B carry out an experiment to measure the period of a
simple pendulum and the results are shown in the table. State which group's
measurements are more consistent and explain why.
______________________________
______________________________
______________________________
______________________________
______________________________
22
1.6 Measuring mass
Mass
In physics, we define mass as a physical property of a body. Mass is a measure
which helps in analyzing how strong is a mutual attraction between two bodies
(Gravitation Concept). It is generally a wrong belief that mass is same as weight,
as mass is a constant quantity, whereas weight is a variable quantity.
Suppose you go to the moon and weigh yourself you will find your weight
measure to be different from that of earth, and as usual, your mass on both
planets will be same. The reason behind difference of weight between earth and
the moon is the gravitational acceleration.
Measuring Mass
Mass is a basic characteristic of matter. It is independent
of temperature, pressure or position of an object in space. Mass is expressed in
different measures, but its standard unit is kilogram or kg. Bureau of Weights and
Measures (BIPM) issue the SI or standard unit. Its prototype is available in many
laboratories across the world.
The unit of measuring mass is always chosen convenience wise, It means if we
want to weigh a large animal, we would prefer kilogram as the unit and if we want
to weigh small size animal, we may switch to another convenient unit.
We measure mass in different forms and with different methods. Consider the
following example:
23

Common objects, humans or other products can be weighed using weighing
machine and common balance, as used in grocery shops

We use gravitational formula, to determine masses of large celestial bodies like
earth, stars, sun and the moon

For measuring sub-atomic and atomic elements, we use mass spectrograph, in
which radius of path of atomic particle is directly proportional to mass of
charged particle moving under the influence of strong electric and magnetic
field.
Digital Balance
Beam Balance
The device on the right is called a beam balance. It is the simplest and probably
the oldest, way of finding the mass of something. You put the object in one pan,
then add standard masses to the other pan until the beam balances in a level
position.
A more modern type of balance is shown on the left. It detects the gravitational
pull on the object on the pan, but gives its reading in units of mass.
The beam balance is really comparing weights rather than masses. Weight is the
downward pull of gravity. The beam balances when the downward pull on one
pan.is equal to the downward pull on the other. However, masses can be
compared because of the way gravity acts on them. If the objects in the two pans
have the same weight, they must also have the same mass.
When using a balance like the one above, you might say that you were 'weighing'
something. However, what you measure in kg is the mass of the object, not its
weight. Weight is a force, measured in force units called newtons.
24
Exercise:
1.
What is 0.0455 kg expressed in standard form?
A 0.455 x 10-1 kg
B 4.55 x 10-2 kg
C 45.5 x 10-3 kg
D 455 x 10-4 kg
2.
Which one of the following measurements is the smallest?
A 1.5 x102 kg
B 1.5 x 107 g
C 1.5 x1012 µg
D 2.3 x109 mg
3.
The Body Mass Index (BMI) of a person is measured by taking the mass of
the person divided by the square of his/her height. Use the information
provided to work out the derived SI unit for BMI.
____________________________________________________________
____________________________________________________________
4.
Which of the following statements is/are correct?
a. One milligram equals one million grams.
b. One thousand milligrams equals one gram.
c. One million milligrams equals one gram,
d. One million milligrams equals one kilogram.
5.
On the Moon, the force of gravity on an object is only about one sixth of its
value on Earth. Decide whether each of the following would give an
accurate measurement of mass if used on the Moon.
a. A beam balance like the one in the photograph above.
____________________________________________________________
____________________________________________________________
b. A digital balance like the one in the photograph above.
____________________________________________________________
____________________________________________________________
25
1.7 Measuring volume
Volume
Volume is the amount of space occupied by an object or substance. It is one of
the derived quantities defined by the International system of Units. The unit of
volume is the cubic metre (m3).
For a number of basic three-dimensional shapes, we can find the volume of an
object quite easily simply by measuring its dimensions and then applying the
correct formula to those measurements to determine its volume.
Volume Formulae for Common 3d Shapes
Shape
Cube
Rectangular prism
(cuboid)
Prism
Pyramid
Cylinder
Cone
Sphere
Formula
Dimension(s) measured
3
l
l = length of each edge
l × w × h l = length, w = width, h = height
B × h
B × h
3
π r 2h
πr2h
3
4
πr3
3
B = area of base, h = height
B = area of base, h = height
r = base radius, h = height
r = base radius, h = height
r = radius of sphere
26
However, not all of the things for which we want to find a volume are regular
three-dimensional shapes, and not all of them are solids. We might want to find
the volume of a gas or a liquid.
In such a case, it is usually not possible to attempt to find the volume of such an
object by taking its measurements. Fortunately, there are a number of techniques
that can be used to find the volume of things that are not regularly shaped solids.
Measuring volume
Liquid The liquid can be poured into a graduated measuring cylinder (as shown
below to the left), and its volume can then be seen by looking at the graduations
on the side of the measuring cylinder. Although the SI unit of volume is the cubic
metre (m3), the volume of a liquid is usually expressed in terms of litres. A litre
has the same volume as a cubic decimeter (a decimeter is one tenth of a metre).
A cubic metre of a liquid is thus equivalent to one thousand litres (1000 L).
How to read the measuring cylinder? When poured into the cylinder, the liquid
forms a meniscus at the top. The meniscus is the curve seen at the top of a liquid
in response to its container. It can be either concave or convex, depending on
the surface tension of the liquid and its adhesion to the wall of the cylinder (as
shown in the picture on the right).
A concave meniscus (or lower meniscus) occurs when the molecules of the liquid
are more strongly attracted to the cylinder than to each other. The liquid appears
27
to "stick" to the edge of the cylinder. Most liquids, including water, present a
concave meniscus.
A convex meniscus (or upper meniscus) is produced when the molecules of the
liquid are more strongly attracted to each other than to the cylinder. A good
example of this shape of meniscus can be seen with mercury in a glass cylinder.
When you read a scale on the side of a graduated cylinder with a meniscus, it's
important that you measure such that the line you are reading is even with the
center of the meniscus. The eye or your line of sight should be in level with the
surface of the liquid.
Regular solid If an object has a simple 3D shape, its volume can be calculated
using the formulae as mentioned in the table before.
For example,
Suppose a cereal box is 10 centimeters long, 4 centimeters wide, and 20
centimeters high. What would be the volume of the box?
Solution:
Volume = Length x Width x Height
Volume = 10 cm x 4 cm x 20 cm
Volume = 800 cm3
Irregular solid Finding the volume of irregularly-shaped solid objects using
measurements is often impractical. We can find the exact volume of an irregularly
shaped solid object relatively easily however, using a method known
as displacement.
28
There are several possible ways to use displacement to find the volume of an
irregularly shaped solid, providing the object is small enough to fit into a
graduated cylinder.
In the first method, we will fill the cylinder about two-thirds full with water. We
will lower the irregularly shaped solid whose volume is to be found, into the
cylinder until it sinks (as shown below left). The first thing to do is to read the
volume of the water in the measuring cylinder and record the value, before and
after immersing the solid into the cylinder. Subtracting the first reading from the
second will give you the volume of the irregularly shaped solid.
In the second method, If the solid is too big for a measuring cylinder, its volume
can be found using a displacement can shown below right. First, the can is filled
up to the level of the spout (this is done by overfilling it and then waiting for the
surplus water to run out). Then the solid is slowly lowered into the water. The
solid is now taking up space once occupied by the water - in other words, it has
displaced its own volume of water. The displaced water is collected in a beaker
and emptied into a measuring cylinder. The volume of the irregular solid is then
recorded.
Method 1
Method 2 (Displacement can)
29
Exercise:
1.
How many cm3 are there in 1m3?
2.
How many cm3 are there in 1 litre?
3.
How many ml are there in 1m3?
4.
A tankful of liquid has a volume of 0.2 m3 . What is the volume in
a. litres
b. cm3
c. ml?
5. The volume of a rectangular block can be calculated using this equation:
volume = length X width X height
Using this information, complete the table below.
Length/cm
Width/cm
Height/cm
Volume of rectangular
block/cm3
2
3
4
?
5
5
?
100
6
7
5
300
?
10
10
50
6. A plastic measuring cylinder is filled with water to the 100 cm3 mark, and a
student measures the column of water in the cylinder and finds that it is 20
cm high.
a. The student pours 10 cm3 of the water out of the cylinder. How high
will the column of water be now?
b. The student then refills the cylinder back to the 100 cm3 mark by
holding it under a dripping tap. She finds that it takes 180 drops of water.
What is the volume of one of these drops?
c. What is the cross-sectional area of the cylinder? Hint: The volume of a
cylinder is given by the equation: volume = cross-sectional area x length.
d. So from answer (c) what is the internal diameter of the tube used to
make the measuring cylinder?
30
1.8 Measuring density
Density
All matter has mass and volume. Mass is a measure of the amount of matter an
object has. Its measure is usually given in grams (g) or kilograms (kg). Volume is
the amount of space an object occupies. There are numerous units for volume
including liters (l), cubic metres (m3).
Mass and volume are physical properties of matter and may vary with different
objects. For example, it is possible for two pieces of metal to be made out of the
same material yet for one piece to be bigger than the other. If the first piece of
metal is twice as large as the second, then you would expect that this piece is also
twice as heavy (or have twice the mass) as the first. If both pieces of metal are
made of the same material the ratio of the mass and volume will be the same.
We define density (ρ) as the ratio of the mass of an object to the volume it
occupies. Density is a measure of how compact a material is - it indicates how
much space or volume a given mass occupies.
The equation is given by: ρ = M / V
(here the symbol M stands for the mass of the object, and V the volume.)
Density has the units of mass divided by volume such as grams per cubic
centimetre (g/cm3) or kilograms per cubic metre (kg/ m3).
The greater the mass of material in a given volume, the greater the density of the
material. The density of a material depends on what it is made up of (atoms and
31
their arrangement) and its physical state. The more spread out the particles, the
lower the material's density - which is why gases have a very low density. The
more closely the particles are packed together, the greater the density - which is
why solids have the highest density.
Example: Using density data from the table above, calculate the mass of steel
having the same volume as 5400 kg of aluminium.
First, calculate the volume of 5400 kg of aluminium.
In this case, ρ is 2700 kg/m3, m is 5400 kg, and V is to be found. So:
ρ=m/V,
V=m/ρ
= 5400 kg / 2700 kg/m3
= 2 m3
This is also the volume of the steel. Therefore, for the steel, ρ is 7800 kg / m3, V is
2 m3, and m is to be found. So:
m = V x ρ = 7800 kg/m3 x 2 m³ = 15 600 kg
So the mass of steel is 15 600 kg.
32
Measuring density:
Density of a liquid To calculate density, we need to know the mass and volume
of the liquid.
Step 1: First, measure mass of the measuring cylinder that is going to hold the
liquid on an electric balance.
Step 2: Then add the liquid to the cylinder and measure and record the mass of
the cylinder + liquid using an electronic balance.
Step 3: To find the mass ‘m’ of the liquid, we subtract the mass of the empty
measuring cylinder from the mass of the liquid and the measuring cylinder.
Step 4: The volume V can be read directly from the measuring cylinder.
Step 5: Then use the equation to calculate density, ρ = m / V.
Density of a regularly shaped solid To calculate density of ‘regularly shaped’
solids, you need to know the formulae volume of the solid.
Step 1: First we calculate the volume ‘V’ of the regularly shaped solid using the
formulae.
Step 2: Then find and record its mass ‘m’ by weighing it on an electric balance.
Step 3: Calculate its density using the formula ρ = m / V.
Density of an irregularly shaped solid It’s difficult to determine the density of an
irregular solid because of its irregular shape. So we use a slightly different method
to calculate the volume of an irregular solid – the displacement method.
33
Step 1: Measure the mass ‘m’ of the irregularly shaped object, like a stone, using
an electronic balance.
Step 2: Partially fill a measuring cylinder with a known volume X of water.
Step 3: Lower the stone gently into the water until its completely immersed,
taking care not to lose water due to splashing. Measure the new volume Y.
Step 4: The volume of the stone is ‘V’ = Y − X.
Step 5: Use the equation to calculate the density ρ = m / V.
Exercise:
1. Aluminium has a density of 2700 kg/m3,
a. What is the density in g/cm3?
b. What is the mass of 20 cm3 of aluminium?
c. What is the volume of 27 g of aluminium?
2. Which block is made of the densest material?
Block
Mass/g
Length/cm
Breadth/cm
Height/cm
A
480
5
4
4
B
360
10
4
3
C
800
10
5
2
D
600
5
4
3
34
3. Use the information in the table of densities at the top of the page to answer
the following:
a. What material, of mass 39 g, has a volume of 5 cm3?
b. What is the mass of air in a room measuring 5m x 2m x 3m?
c. What is the volume of a storage tank which will hold 3200 kg of petrol?
d. What mass of lead has the same volume as 1600 kg of petrol?
4. The mass of a measuring cylinder and its contents are measured
before and after putting a stone in it.
Which of the following could you
calculate using measurements taken
from the apparatus on the right?
a. the density of the liquid only
b.
the density of the stone only
c.
the densities of the liquid and
the stone.
5. A plastic bag filled with air has a volume of 0.008 m3. When air in the bag is
squeezed into a rigid container, the mass of the container (with air) increases
from 0.02 kg to 0.03 kg. Calculate the density of the air in the bag.
6. A golden-colored cube is handed to you. The person wants you to buy it for
400 dirhams, saying that is a gold nugget. You pull out your Physics text and
look up gold in the density table, and read that its density is 19.3 g/cm3. You
measure the cube and find that it is 2 cm on each side, and weighs 40 g. What
is its density? Is it gold? Should you buy it?
7. Activity (To determine the density of a gas): A gas can be compressed so the
density of a gas can change
35
1. Place a beaker inside a bath filled with water so that the beaker is about ½
filled with water and the other ½ air. (you might have to let some air out by
tilting the beaker.)
2. Add water to the bath.
a.
What
happens
to
the
water
level
inside
the
beaker?
___________________
b. Has any air escaped the beaker? Has the amount of air inside the beaker
changed? __________________________________________________
c. What happens to the density of the air inside the beaker when you add
water? ____________________________________________________
36
1.9
Scalars and Vectors
Introduction
Mathematics and Science were invented by humans to understand and describe
the world around us. A lot of mathematical quantities are used in Physics to
explain the concepts clearly. A few examples of these include force, speed,
velocity, and work. These quantities are often described as being a scalar or a
vector quantity. Scalars and vectors are differentiated depending on their
definition.
Consider a car that is travelling from city A to city B. The distance travelled by the
car can be calculated by multiplying the average speed of the car and the time
taken. However, we cannot find out how far the car is from its starting point
unless we are told the direction of travel. Therefore, direction must be specified
for some quantity.
What Is Scalar Quantity?
Scalar quantity is defined as the physical quantity with magnitude and no
direction.
Some physical quantities can be described just by their numerical value (with their
respective units) without directions (they don’t have any direction). The addition
of these physical quantities follows the simple rules of the algebra. That is only
their magnitudes are added.
37
Examples of Scalar quantity:
There are plenty of scalar quantity examples, some of the common examples
are:








Mass
Speed
Distance
Time
Area
Volume
Density
Temperature
What Is Vector Quantity?
A vector quantity is defined as the physical quantity that has both direction as well
as magnitude.
The direction of a vector can be given in a written description:
For example,

Force, eg 20 newtons (N) to the left.

Displacement, eg 50 kilometres (km) east.

Acceleration, eg 9.8 metres per second squared (m/s²) downwards.
Or else direction of a vector can be drawn as an arrow. The length of an arrow
represents the magnitude of the quantity:
The diagrams show three examples of vectors, drawn to different scales.
38
Examples of vector quantities:
Vector quantity examples are many, some of them are given below:








Force
Acceleration
Displacement
Momentum
Velocity
Weight
Electric field
Magnetic field
Scalar & Vector addition
Adding Scalars:
Scalar quantities are added by ordinary algebraic methods.
Examples:
• 5 cm³ + 10 cm³ = 15 cm³
• 25 m + 46 m = 71 m
• 213 m² + 236 m² = 449 m²
Similarly scalar quantities can be subtracted by subtracting one value from
another.
Example:
A room is heated from 12°C to 21°C using a radiator. Calculate the increase in
temperature.
21°C - 12°C = 9°C
Point to remember: You must make sure that the scalar quantities are all
in the same units before adding or subtracting. It may involve converting
quantities into SI units before completing the calculation.
39
Adding Vectors:
Vectors can be added together to produce a resultant vector. The rules for doing
this, however, are slightly different to scalars:

If two vectors point in the same direction, the resultant vector will also have
the same directions and its value will be the result of adding the magnitudes
of the two original vectors together.
 If two vectors point in opposite directions then subtract the magnitude of one
of the vectors from the other one. The direction of the resultant will be the
same as the larger of the two original vectors.
Diagram showing the result of adding two aligned vectors (forces) together
If the two vectors point in completely different directions, then the value of the
resultant vector can be found graphically using two methods:
1. Tip to tail vector addition



Draw an arrow representing the first vector.
Now starting at the head of the first arrow, draw a second arrow representing
the second vector.
The resultant vector can be found by drawing an arrow going from the tail of
the first vector to the tip of the second vector.
Diagram showing an example of the “tip-to-tail” addition of two vectors
40
2. Parallelogram rule of vector addition
If two vectors act at an angle to one another and act from a common point,
parallelogram method is used to find the resultant of the two vectors. In a
parallelogram method, the two vectors are represented by the adjacent sides
of the parallelogram while the diagonal represent the resultant vector.
A ship being pulled forward by the resultant force from the tugs
The parallelogram rule is a method of finding the resultant in situations like the
one above, where the vectors are not in line. It works like this:
To find the resultant of two vectors (for example, forces of 30 N and 40 N acting
at a point O, as in the diagram below):
i. On paper, draw two lines from O to represent the vectors. The directions must
be accurate, and the length of each line must be in proportion to the magnitude
of each vector.
ii. Draw in two more lines to complete a parallelogram.
iii. Draw in the diagonal from O and measure its length. The diagonal represents
the resultant in both magnitude and direction. (Below, for example, the resultant
is a force of 60 N at 26° to the horizontal.)
41
Exercise:
1. Given below is a list of quantities. Categorize each quantity as being either a
vector or a scalar.
20 degrees Celsius
5 mi., North
256 bytes
5m
30 m/sec, East
4000 Calories
2. How is a vector different from a scalar? Give an example of each.
_________________________________________________________________
_________________________________________________________________
3. Forces of 12 N and 5 N both act at the same point, but their directions can be
varied.
a) What is their greatest possible resultant?
_________________________________________________________________
b) What is their least possible resultant?
_________________________________________________________________
c) If the two forces are at right angles, find by scale drawing or otherwise the size
and direction of their resultant.
42
4. At lift-off, a space rocket has an engine force of 45000N. The weight of the
rocket is 38 000 N. The resultant force on the rocket is ________
A.
B.
C.
D.
83,000 N upwards
7,000 N upwards
7,000 N downwards
83,000 N downwards
5. Two tugboats are towing a cargo ship as shown below. Tugboat A exerts a force
of 15,000 N at a 30° angle while tugboat B exerts a force of 20,000 N at a 50°
angle. Determine the magnitude and direction of the resultant force acting on the
cargo ship.
43
UNIT 2
ELECTRICITY
44
2.1
Electric Charge
Structure of atom
Matter is made up of atoms. Atoms consist of three basic particles: protons,
electrons, and neutrons. The nucleus (center) of the atom contains the protons
(positively charged) and the neutrons (no charge). Electrons (negatively charged)
are found in the outermost regions of the atom. Electrons are charged particles
that are transferred from one object to another when they are rubbed together.
Electric charge is the property of the particles that make up atoms.
What is electricity?
Electricity is a form of energy. Electricity is the flow of electrons. Electric charge,
or electricity', can come from batteries and generators. But some materials
become charged when they are rubbed. Their charge is sometimes called
electrostatic charge or 'static electricity. It causes sparks and crackles when you
take off a pullover, and if you slide out of a car seat and touch the door, it may
even give you a shock.
Unit of Charge
The S.I or Standard unit of electric charge is Coulomb. Its symbol is C and 1 C is
defined as the charge flowing through a wire in 1 sec if the current flowing in the
wire is 1 A.
Q = I.t
(where Q is charge, I is current and t is time)
45
Types of electric charges
There are two types of electric charge: Positive charge & Negative charge
Since all materials on earth are made up of atoms, which contain the positively
charged protons and negatively charged electrons, any imbalance in the number
of protons and electrons, will cause the material to be charged or ionised. A loss
of electrons will make it positively charged and a gain of electrons will make
it negatively charged.
For example, Polythene and Perspex can be charged by rubbing them with a dry,
woolen cloth. When two charged polythene rods are brought close together, they
repel (try to push each other apart). The same thing happens with two charged
Perspex rods. However, a charged polythene rod and a charged Perspex rod
attract each other.
When you rub the balloon, for example on the carpet, electrons (with a negative
charge) build up on the surface of the balloon (they are transferred from the
carpet to the balloon).
Properties of electrical Charge
When two charged objects are brought close together, there will be a force
between those objects.
Like charges repel each other. Unlike charges, attract.
The closer the charges, the greater the force between them.
Where do charge come from?
Normally, atoms have equal numbers of electrons and protons, so the net
(overall) charge on a material is zero. However, when two materials are rubbed
together, electrons may be transferred from one to the other. One material ends
up with more electrons than normal and the other with less. So one has a net
negative charge, while the other is left with a net positive charge. Rubbing
materials together does not make electric charge. It just separates charges that
are already there.
46
Exercise:
1. Time for fun activity
STEP
Observation
Balloon rubbed with dry hair is
brought closer to a suspended balloon
Balloon rubbed with dry hair is
brought closer to a suspended balloon
which is also rubbed with dry hair
Balloon rubbed with dry hair is
brought closer to small pieces of paper
2. Give an example of where electrostatic charge might be a hazard.
_________________________________________________________________
_________________________________________________________________
3. How can the build up of electrostatic charge be prevented?
_________________________________________________________________
_________________________________________________________________
4. Does the weather affect static electricity?
_________________________________________________________________
_________________________________________________________________
5. How does lightning occur?
_________________________________________________________________
_________________________________________________________________
47
2.2
Charging
Charging by friction
Objects can be given a charge by rubbing them with another object. This is
called charging by friction.
When an object gets charged it is either positively charged or negatively
charged.
Most object are neutral (they are not charged) this is because they have an equal
amount of protons and neutrons. An object would be positively charged if it has
less electrons than protons and an object would be negatively charged if it has
more electrons than protons.
When insulating materials rub against each other, they may become
electrically charged. Electrons, which are negatively charged, may be ‘rubbed off’
one material and on to the other. The material that gains electrons becomes
negatively charged. The material that loses electrons is left with a positive charge.
For example, when a polythene rod is rubbed with a duster, the friction causes
electrons to gain energy. Electrons gain enough energy to leave the atom and ‘rub
off’ onto the polythene rod.
 The
polythene rod has gained electrons, giving it a negative charge.
 The
duster has lost electrons, giving it a positive charge.
48
Thinking time
Why do you get shock when you touch a
metal door knob after rubbing your feet
against carpet?
Exercise:
Let us check what we have learnt:
1) The negatively charged particles in an atom are called _____.
2) Electric charges that are alike _______ each other (attract/ repel).
3) If a substance has a higher number of electrons than protons on its surface,
what type of charge does it have?
4) Like charges repel each other and unlike charges attract.
The girl's hair and the comb have _______
5) A polythene rod is rubbed using a woolen cloth. The
rod gains a negative charge.
a) what can you say about the charge gained by the cloth?
b) Will the rod and the cloth attract or repel each other?
6) Draw appropriate charges on each material and show the transfer of charges
after rubbing.
Balloon
Balloon
Cloth
Balloon and cloth before rubbing
Cloth
Balloon and cloth after rubbing
49
7) What happens if the balloon in stage 2 of Question 6 is in contact with a
metal strip? Explain.
8) Why a PC monitor is covered with dust?
.................................................................................................................................
.................................................................................................................................
9) Figure shows a copper rod and a piece of cloth. What happens when you rub
the rod with the cloth? Explain your answer.
50
2.3
Earthing and Induced charges
In the previous lesson, we discussed the process of charging an object by friction
or rubbing. Friction charging is a very common method of charging an object.
However, it is not the only process by which objects become charged. We have
charging by induction and conduction. Charging by conduction involves the
contact of a charged object to a neutral object. In this chapter, the charging by
induction method will be discussed.
Induction charging is a method used to charge an object without actually touching
the object to any other charged object. An understanding of charging by induction
requires an understanding of the nature of a conductor.
Charging by induction
In the induction process, a charged object is brought near but not touched to a
neutral conducting object.
A sphere is mounted on an insulating material. The sphere has both positive and
negative charge and as the negatively charged rod is brought near to the sphere,
the negative charge in sphere are repelled by the rod (due to same charge) and
move to the other side of sphere. The overall object is neutral (i.e., has the same
number of electrons as protons), there is an excess of positive charge on one side
of the object and an excess of negative charge on the opposite side of the object.
Earthing
The negative charge flows into the ground when we connect the metal sphere
to the ground by a conducting wire.
51
The sphere acquires a positive charge as we disconnect the ground. The positive
charge is uniformly distributed in sphere as the negatively charge rod is removed.
A ground is simply a large object that serves as an almost infinite source of
electrons or sink for electrons.
Now let us make the metal sphere negative
Which rod will you use?
52
Exercise:
Let us check what we have learnt:
1) In the fig, S is a metal sphere on an insulating base. R is a negatively charged
rod placed close to S.
(i)
Name the particle in S that move when R is brought close to S.
--------------------------------------------------------------------------------------
(ii)
On Fig add + sign and - sign to suggest the result of this movement.
(iii)
Describe the actions which now need to take place so that S become
positively charged with the charge distributed evenly over its surface. A
positively charged object is not available.
2) Spheres 1, 2, 3 and 4 are electrically charged. The charge on sphere 1 is
positive and the charge on sphere 4 is negative. We do not know the type of
charge on sphere 2 or on sphere 3. When spheres 1 and 2 are brought near each
other, they attract each other. When spheres 3 and 4 are brought near each
other, they repel each other.
53
+
1
2
3
4
What type of charge is on sphere 2 and on sphere 3?
A The charge on sphere 2 is positive and the charge on sphere 3 is positive.
B The charge on sphere 2 is negative and the charge on sphere 3 is negative.
C The charge on sphere 2 is positive and the charge on sphere 3 is negative.
D The charge on sphere 2 is negative and the charge on sphere 3 is positive.
3) We are given four spheres, A, B C and D. Sphere A is positively charged and
the charges on spheres B, C and D are unknown. The following diagram shows
what happens to these spheres if we suspend them two by two close to each
other.
A
B
B
C
C
D
Given the diagram above, what are the charges on spheres C and D?
A Sphere C is positively charged and sphere D is negatively charged.
B Sphere C is positively charged and sphere D is positively charged.
C Sphere C is negatively charged and sphere D is negatively charged.
D Sphere C is negatively charged and sphere D is positively charged.
4) When an oil tanker car has arrived at its destination, it prepares to empty its
fuel into a reservoir or tank. Part of the preparation involves connecting the
body of the tanker car with a metal wire to the ground. Suggest a reason for
why is this done.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
54
2.4 Electric Field
Electric Field
An electric field is a region where charges experience a force. Electric field around
a charged body exists if electric forces are exerted by it on another charged body
in that region. The direction of electric field at a point is the direction in which a
point charge would experience or move (under the influence of the field) if placed
at that point.
Electric Field lines
Electric field line around positive charge and negative charge is shown in below
figure.
The electric field lines should be drawn perpendicular to the surface of the
charged object. The field lines never intersect.
Electric field strength is greatest at locations closest to the surface of the charge
and least at locations further from the surface of the charge.
When a positively charged object is brought near to another positive charged
object, it experience a force of repulsion.
55
Electric field lines point away from positive charges and towards negative
charges.
 The field lines around a charged conducting sphere are as if the charge was
concentrated at the centre of the sphere.
 The field lines between two charged plates go in straight lines from the
positive plate to the negative plate and are equally spaced apart.
The below figure shows that the magnitude of charge on C is greater than B
which is greater than A
Electric field patterns
i) Radial electric field due to point charge:
The electric field lines radiating from an isolated positively charged conducting
sphere are the field lines emerging at right angles to its surface as shown in the
figure.
56
ii) Electric field line patterns for objects with equal amount of charge:
A positively and a Negatively charged object
Two positively charged objects
iii) Electric field line pattern between two oppositely charged parallel plates:
iv) Electric field line patterns for objects with unequal amount of charge:
57
Exercise:
Let us check what we have learnt:
1) Observe the electric field lines below for various configurations. Rank the
objects according to which have the greatest magnitude of electric charge,
beginning with the smallest charge.
2) Several electric field line patterns are shown in the diagrams below.
a) Which of these patterns are incorrect? _________
b) Explain what is wrong with all incorrect diagrams.
3) Use your understanding of field lines and identify the charges.
58
2.5
Conductors and Insulators
When some materials gain charge, they lose it almost immediately. This is
because electrons flow through them or the surrounding material until the
balance of negative and positive charge is restored. Based on the behavior of the
materials they are classified as conductors and insulators.
Conductors
The materials which allows the electric current or heat to pass through it. The
electrons in a conductor can freely move. Copper, Aluminium, silver, mercury, etc.
are some of the examples of the conductor. Silver is the best conductor of
electricity.
Insulators
The materials which do not allow the electric current, or heat to pass through it
such type of material is called an insulator. The covalent bond between the atoms
of an insulator are very strong. Thus, the electrons or charges do not move
freely. The insulator is mainly used for separating the conductor and for
supporting the electrical equipment. It is also used in an electrical cable. Paper,
wood, porcelain, etc., are some of the examples of an insulator. Graphite is the
only non-metal that can conduct electricity.
59
Semiconductors
The Semiconductors, such as Germanium, Silicon, etc. has electrical property
between that of a conductor and an insulator. Semiconductors have some useful
properties and are being extensively used for the preparation of solid state
devices like the diode, transistor, etc.
Exercise:
Let us check what we have learnt:
1) Why are electric wires coated in plastic?
___________________________________________________________________________________
2) Which is the best conductor of electricity?
___________________________________________________________________________________
3) Why do we wear woolen clothes in winter?
___________________________________________________________________________________
4) What makes copper a better electrical conductor than polythene?
_________________________________________________________________
_________________________________________________________________
5) Why is it easy to charge polythene by rubbing, but not copper?
_________________________________________________________________
_________________________________________________________________
60
6) Complete the word search by finding the words given below.
61
UNIT 3
EARTH & SPACE
62
3.1
Structure of the Earth
Structure of the Earth
Our planet the Earth is the third planet from the sun. The shape of the Earth
although considered to be spherical, is actually oblate spheroid (squashed at the
North and South poles).
Formed billions of years ago, the earth comprises of several layers. A layer is
defined as the thickness of a material that is laid out. In the case of the earth,
these layers are composed of mostly rock and iron. Each layer has its own
characteristics and purpose.
The structure of the earth is divided into four major components: the crust,
the mantle, the outer core, and the inner core. Each layer has a unique chemical
composition, physical state, and can impact life on Earth's surface.
Crust
The crust is the outermost layer of the planet. It is cool, thin and brittle shell made
of rock. This layer makes up only 1% of the entire volume of the Earth. The crust
is very thin, relative to the radius of the planet. There are two very different types
of crust, each with its own distinctive physical and chemical properties.
63
a) Oceanic crust the oceanic crust is composed of dense material such as iron
magnesium silicate igneous rocks (like basalt). Oceanic crust is about 6 km
(4 miles) thick. Sima is a term used to describe oceanic crust rock, which is
short for magnesium silicate.
b) Continental crust is made up of many different types of igneous,
metamorphic, and sedimentary rocks. The average composition is granite,
which is much less dense than the mafic igneous rocks of the oceanic crust.
Because it is thick and has relatively low density, continental at a higher
elevation on the mantle than oceanic crust.
Mantle
The mantle is the mostly-solid bulk of Earth's interior. The mantle lies between
Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is
about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84% of
Earth’s total volume.
The rocks that make up Earth’s mantle are mostly silicates—a wide variety
of compounds that share a silicon and oxygen structure. Common silicates found
in the mantle include olivine, garnet, and pyroxene. The other major type of rock
found in the mantle is magnesium oxide. Other mantle elements include iron,
aluminum, calcium, sodium, and potassium.
Core
Beneath the mantle you'll find the core. Earth's core is the deepest, hottest layer,
and it's made up of two layers itself: the outer core and inner core.
64
Earth’s outer core is fluid layer about 2400km thick and composed of mostly Iron
and Nickel.
The inner core is solid and is 90% iron. The inner core of the Earth has
temperatures and pressures so great that the metals are squeezed together and
are not able to move about like a liquid, but are forced to vibrate in place as a
solid.
Density increases from Crust to core.
Exercise:
Let us check what we have learnt:
1) Compare the structure of Earth with hard boiled Egg.
Name the part of the Earth that is like the yolk of an egg.
_______________________________________________________________
2) The Earth is more like a soft-boiled egg. Explain why the Earth is more like a
soft-boiled egg.
_______________________________________________________________
_______________________________________________________________
3) Which is the most dense layer?
_______________________________________________________________
65
4) Label the four layers of the Earth.
5) Draw lines on the chart to match the layer to its description.
6) Why is the outer core liquid while the inner core is solid?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
66
3.2
Tectonic plates
Tectonic plates
The theory of plate tectonics was put forward in the 1960’s. It coincided with a
time when a large amount of research was being conducted about the ocean
floors. Since then better understanding and technology have refined the theory
to explain how the Earth has been shaped.
The theory states that the Earth’s crust is broken into large and smaller pieces
called plates that glide over the mantle, the rocky inner layer above the core. The
plates act like a hard and rigid shell compared to Earth’s mantle. These massive
slabs of solid rock are made up of both continental and oceanic lithosphere (the
crust and uppermost mantle).
Moving plates
The earth’s lithosphere is composed of seven or eight major plates and many
minor plates. The lithosphere is a rigid outermost shell of earth and is broken up
into tectonic plates. When these plates meet, there is relative motion between
them.
Volcanic activity, earthquakes, mountain-building and oceanic trench formation
occur along these plate boundaries. The sizes of these plates vary greatly from a
few hundred to thousands of kilometres across. The relative movement of the
plates typically ranges from zero to 100 mm annually.
67
Causes of moving plates
It affects humans in several important ways.




It causes earthquakes
It causes volcanism
It induces recycling of elements within the biosphere and between the
geosphere and biosphere
It causes mountain-building
How do tectonic plates move?
The main impetus behind plate tectonics is convection in the mantle. Convection
currents are movements of heat within the mantle. Material in the mantle is
heated by the decay of radioactive isotopes in the core. This causes convection
currents in the molten mantle material. Mantle expands, rises and spreads out
beneath the plates. Plates are dragged along and move away from each other.
Subsequently, the hot molten mantle cools slightly and sinks, pulling the plates
along. Hence plates move towards each other. The sinking mantle material heats
up again as it nears the core and the whole process repeats.
68
How many plates are there?
There are nine significant plates, as indicated by World Atlas. These plates are
named according to the landforms found on them. The nine significant plates are
North American, Pacific, Eurasian, African, Indo-Australian, Australian, Indian,
South American and Antarctic.
The biggest plate is the Pacific Plate at 39,768,522 square miles (103,000,000
square kilometers). Its vast majority is situated under the sea. The plate is moving
northwest at a speed of around 2.75 inches (7 cm) every year.
There are likewise numerous smaller plates all through the world.
Exercise:
1. The crust of the Earth is made up of plates. They move and rub against each
other. This can cause earthquakes.
The plates move because of………………………………………………………… currents in
the....................................................................................
2. Uneven heating inside the Earth makes the currents. This can be shown by
heating some water in a beaker.
The water is heated and the polystyrene starts to move. Draw an arrow (→)
on the diagram to show in which direction the polystyrene starts to move.
3. Sections of the Earth’s surface rub against each other. This can cause an
earthquake if the sections suddenly slide past each other. Irfan set up the
apparatus as shown. The block slides over the table when enough weights are
put in the pan.
69
Irfan carefully added weights to the pan.
a. Complete this sentence:
He kept adding weights until
.................................................................................................................................
.................................................................................................................................
b. Give two reasons why he repeated the experiment three times.
1...............................................................................................................................
.................................................................................................................................
2...............................................................................................................................
.................................................................................................................................
c. Complete this sentence:
Each time he repeated the experiment he had to make sure that he placed the
block
.................................................................................................................................
.................................................................................................................................
d. Give two reasons why it is important to use the same block for each
experiment.
70
1...............................................................................................................................
.................................................................................................................................
2...............................................................................................................................
.................................................................................................................................
Next, he placed a piece of cloth on the table. He placed the block on the cloth.
He did the experiment again with the block on the cloth. Then he repeated the
experiment by replacing the cloth with different materials. The table shows his
results.
e. Work out the average value for plastic and complete the table.
f. Irfan wants to find the average value for cardboard. Write down the number he
should not use when he works out the average.
............................... g
g. Name the material that needs the smallest weight to make the block slide
over it.
.................................................................................................................................
.................................................................................................................................
h. Earthquakes cause more damage if the sections of the Earth’s surface do not
slide easily. Name the material used in the experiment over which the block did
not slide easily.
.................................................................................................................................
................................................................................................................................
71
3.3
Earthquakes
Plate boundaries
The plates float on top of the asthenosphere. Convection currents rise in the
asthenosphere and spread out beneath the lithosphere, causing the movement
of Earth’s plates. As the plates move, they produce changes in Earth’s surface,
including volcanoes, mountain ranges, and deep-ocean trenches. The edges of
different pieces of the lithosphere meet at lines called plate boundaries. Faults—
breaks in Earth’s crust where rocks have slipped past each other—form along
these boundaries.
Plate tectonics cause earthquakes and volcanoes. The point where two plates
meet is called a plate boundary. Earthquakes and volcanoes are most likely to
occur either on or near plate boundaries.
Types of plate boundaries
There are three types of plate boundaries: transform boundaries, divergent
boundaries, and convergent boundaries. The plates move at amazingly slow
rates, from about 1 to 24 cm per year. They have been moving for tens of millions
of years.
1. A transform boundary is a place where two plates slip past each other,
moving in opposite directions. Earthquakes occur frequently along these
boundaries.
2. The place where two plates move apart, or diverge, is called a divergent
boundary. Most divergent boundaries occur at the mid-ocean ridge. When a
divergent boundary develops on land, two slabs of Earth’s crust slide apart. A
deep valley called a rift valley forms along the divergent boundary.
72
3. The place where two plates come together, or converge, is a convergent
boundary. When two plates converge, the result is called a collision. When
two plates collide, the density of the plates determines which one comes out
on top. Oceanic crust is more dense than continental crust.
Earthquakes
The movement of the Earth’s plates causes earthquakes. An earthquake is the
result of a sudden release of energy that causes the Earth’s crust to shake,
sometimes violently. Each day, there are at least 8000 earthquakes on the Earth.
In a typical year, about 49 000 earthquakes are actually strong enough to be felt
and noticed by people and an average of 18 of these can cause serious damage
to buildings and possibly injure and kill people.
Most of the world’s earthquakes (90% of them and 81% of the largest) take place
along the Pacific Ring of Fire – a 40 000 km long, horseshoe-shaped zone found
along the edge of the Pacific Ocean. As plates move, the rocks on their edges may
become locked together until, at the weakest point along a plate boundary – a
fault line – they tear apart, or rupture, and this releases the strain.
What causes an earthquake?
An earthquake is the shaking and vibration of the Earth's crust due to movement
of the Earth's plates (plate tectonics). Earthquakes can happen along any type of
plate boundary.
Earthquakes occur when tension is released from inside the crust. Plates do not
always move smoothly alongside each other and sometimes get stuck. When this
happens pressure builds up. When this pressure is eventually released, an
earthquake tends to occur.
73
The point inside the crust where the pressure is released is called the focus. The
point on the Earth's surface above the focus is called the epicentre. Earthquake
energy is released in seismic waves. These waves spread out from the focus. The
waves are felt most strongly at the epicentre, becoming less strong as they travel
further away. The most severe damage caused by an earthquake will happen
close to the epicentre.
Predicting earthquakes
Earthquakes are not as easy to predict as volcanic eruptions. However, there are
still some ways of monitoring the chances of an earthquake:

Laser beams can be used to detect plate movement.

A seismometer is used to pick up the vibrations in the Earth's crust. An
increase in vibrations may indicate a possible earthquake.

Seismograph is the print out/graph produced by the seismometer.

Richter scale is the scale traditionally used to record the magnitude of an
earthquake.

Movement Magnitude Scale is the scale often used currently to record the
magnitude of earthquakes (it is more accurate for large earthquakes than the
Richter scale.

Radon gas escapes from cracks in the Earth's crust. Levels of radon gas can be
monitored - a sudden increase may suggest an earthquake.
Many of the prediction techniques used to monitor earthquakes are not 100 per
cent reliable. Planning and preparing for an earthquake is therefore very
important.
Exercise:
1. Complete the compare/contrast table to show how plates move at the
different types of plate boundaries.
Plate Movement
Type of Plate Boundary How Plates Move
Divergent boundary
a.
Convergent boundary
b.
Transform boundary
c.
74
2. Fill in the blank to complete each statement.
i.
_______________ is the scale traditionally used to record the magnitude
of an earthquake.
ii.
Breaks in Earth’s crust where rocks have slipped past each other are called
.
The lithosphere is broken into separate sections called ________________.
iv. A(n)
is a deep valley on land that forms along a
divergent boundary.
iii.
v.
The most severe damage caused by an earthquake will happen close to
the _______________________.
3. Irfan drew this graph. It shows the number of earthquakes for each year.
Describe the pattern shown on the graph.
.................................................................................................................................
.................................................................................................................................
4. Irfan draws a pie chart to show the number of earthquakes in spring, summer
autumn and winter in one year.
75
Name the season that has the largest number of earthquakes.
.................................................................................................................................
5. Underline the word in this list which best describes earthquakes.
predictable
tested
unpredictable
untested
6. Waves spread out from the place where an earthquake starts. A scientist at A
can say how far away the earthquake happened. But he cannot tell the direction.
He draws a circle on a map. A scientist at B also draws a circle for the distance
from him.
a. Draw an arrow (→) pointing to where the earthquake could or has happened.
b. Give one reason why it is important to discover where an earthquake has
happened.
.................................................................................................................................
.................................................................................................................................
7. Label each figure by writing the type of plate boundary it shows.
1. _______________
2. ________________
76
3.__________________
8. Answer the following questions in your notebook.
i.
ii.
Describe what happens when a) two plates carrying oceanic crust collide, b)
two plates carrying continental crust collide, and c) a plate carrying oceanic
crust collides with a plate carrying continental crust.
Explain what force caused the movement of the continents from one
supercontinent to their present positions.
9. Designing Experiment- Modeling Mantle Convection Currents
Problem
How might convection in Earth’s mantle affect tectonic plates?
Materials
■
large plastic bottle
■
food coloring
■
small glass jar
aluminum foil
■
rubber band
■
■
■
several pieces of paper about 0.5 cm square
tap water
Procedure
1. Fill the large bottle about half full with cold tap water.
2. Partly fill the small jar with hot tap water and stir in 6 drops of food coloring.
Carefully add enough hot water to fill the jar to the brim.
3. Cover the top of the jar with aluminum foil and secure with a rubber band.
4. Carefully lower the jar into the bottle of ice water.
5. Place the pieces of paper on the surface of the water.
6. Without disturbing the water, use the tip of the pencil to make two small holes
about 2 mm in diameter in the aluminum foil covering the jar.
7. Predict what will happen to the colored water and to the pieces of paper
floating on the surface.
8. Observe the contents of the jar as well as the paper pieces on the surface of the
water.
77
Analyze and Conclude
Write your answers in the spaces provided.
1. Describe what happened to the colored water and to the pieces of paper
after the holes were punched in the material covering the jar.
_____________________________________________________________
_____________________________________________________________
2. How did your prediction compare with what actually happened to the
colored water and pieces of paper?
_____________________________________________________________
_____________________________________________________________
3. What type of heat transfer took place in the bottle? Describe how the
transfer occurred.
_____________________________________________________________
_____________________________________________________________
4. Which part of your model represents a tectonic plate? Which part represents
Earth’s mantle?
_____________________________________________________________
_____________________________________________________________
5. How well do you think this lab modeled the movement of Earth’s plates?
What similarities exist between this model and actual plate movement?
What factors weren’t you able to model in this lab?
_____________________________________________________________
_____________________________________________________________
Extended Work (Class notebook):
Repeat this activity, but develop a plan to measure the temperature of the water
inside the large bottle. Is there a difference in temperature between the water’s
surface and the water near the top of the small jar? Do you observe any change
in the convection currents as the water temperature changes?
78
3.4
The Solar System
Solar System
Solar system is the collection of eight planets and their moons in orbit round the
sun, together with smaller bodies in the form of asteroids, meteoroids, and
comets.
The Sun, Moon, and brightest planets were visible to the naked eyes of ancient
astronomers, and their observations and calculations of the movements of these
bodies gave rise to the science of astronomy. Today the amount of information
on the motions, properties, and compositions of the planets and smaller bodies
has grown to immense proportions, and the range of observational instruments
has extended far beyond the solar system to other galaxies and the edge of the
known universe.
Earth-launched space probes and landers have gathered data on planets, moons,
asteroids, and other bodies, and this data has been added to the measurements
collected with telescopes and other instruments. All this information is
scrutinized in attempts to understand in detail the origin and evolution of the
solar system—a goal toward which astronomers continue to make great strides.
79
The Sun
The Sun is by far the largest object in our solar system, containing 99.8 percent of
the solar system's mass. It sheds most of the heat and light that makes life
possible on Earth and possibly elsewhere. Its gravity holds the solar system
together, keeping everything from the biggest planets to the smallest particles of
debris in its orbit. There are billions of stars like our Sun scattered across the Milky
Way galaxy. The Sun does not have any rings. Its core is about 27 million degrees
Fahrenheit (15 million degrees Celsius).
Planets orbit the sun in oval-shaped paths. The planets are - Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Inner planets
There are four inner planets — Mercury, Venus, Earth and Mars. They are made
up mostly of iron and rock. They are known as terrestrial or earthlike planets
because of their similar size and composition.
Outer Planets
The gas giants of our solar system are Jupiter, Saturn, Uranus and Neptune. These
four large planets, also called Jovian planets. Jupiter and Saturn are substantially
larger than Uranus and Neptune, and each pair of planets has a somewhat
different composition.
Mercury
Mercury is the closest planet to the sun and is also
the smallest planet.
It has no satellites or rings. Due to its close
proximity to the sun, the temperatures are
extremely hot. Mercury has no atmosphere. Since
Mercury is the closest planet to the sun, the
temperature on the surface of Mercury is very
high. The temperature of the surface of Mercury changes from day to night.
80
Before the sunrise, the temperature on the surface of Mercury is as low as -170 °C
and by noon, the temperature on the surface of Mercury rises to about 400 °C.
The change in temperature on the surface of Mercury is due to its rotation and
lack of atmosphere. During the day, the temperature is high and during the night,
the temperature drops well below freezing. Due to the extremely high
temperatures and solar radiation on the surface of mercury during the day, the
surface of the planet is dry and barren.
Venus
Venus orbits our Sun, a star. Venus is the
second closest planet to the sun at a distance
of about 67 million miles (108 million km).
Venus is similar in structure and size to Earth.
One day on Venus lasts 243 Earth days
because Venus spins backwards, with its sun
rising in the west and setting in the east.
Venus has no moons and no rings.
It is made up of a central iron core and a rocky mantle, similar to the composition
of Earth. Its atmosphere is mainly made up of carbon dioxide (96%) and nitrogen
(3%), with small amounts of other gases.
Earth
Earth is the fifth largest planet in the solar
system and is the third planet from the Sun.
Earth is a rocky planet with a solid and
dynamic surface of mountains, canyons,
plains and more. Most of our planet is
covered in water.
Earth's atmosphere is rich in nitrogen and
oxygen. The ozone layer is a natural layer of
gas in the upper atmosphere that protects humans and other living things from
harmful ultraviolet (UV) radiation from the sun.
The Moon is Earth’s only natural satellite. Earth has no rings around it.
81
Mars
Mars is the fourth planet from the Sun and
the second-smallest planet in the Solar
System.
It is called the Red Planet because its iron-rich
dust gives it landscape a rusty-red color. Its
length of year is 687 Earth Days. It has 2
moons namely Phobos and Deimos. Mars has
about one tenth of the mass of Earth.
Jupiter
Fifth in line from the Sun, Jupiter is the largest
planet in the solar system. Jupiter is a gas giant.
It does not have a solid surface being comprised
mostly out of swirling gases and liquids such as
90% hydrogen, 10% helium – very similar to the
sun.
Jupiter rotates once every 10 hours – A Jovian
day – thus it has the shortest day of all the
planets in the solar system. There are 79
known moons of Jupiter.
Jupiter is known to have 4 sets of rings: the
halo ring, the main ring, the Amalthea gossamer ring, and the Thebe
gossamer ring.
Jupiter's Great Red Spot is a gigantic storm that is about twice as wide as Earth. It
is generally reddish in colour and slightly oval.
Saturn
Saturn is the sixth planet from the Sun and the
second-largest in the Solar System, after
Jupiter. Saturn's atmosphere is made up mostly
of hydrogen (H2) and helium (He). Saturn has
the most spectacular ring system, with seven
rings and several gaps and divisions between
them.
82
Saturn is the only planet in our solar system whose average density is less than
water.
Uranus
Uranus is the seventh planet from the Sun. It's
not visible to the naked eye, and became the
first planet discovered with the use of a
telescope. It is the third largest planet in our
Solar System.
Uranus
is
made
of water, methane,
and ammonia fluids above a small rocky
center. Its atmosphere is made of hydrogen
and helium like Jupiter and Saturn, but it also
has methane.
Uranus
has
27
known
moons.
Five
major moons
are Miranda, Ariel, Umbriel, Titania and Oberon. Unlike any other planet, Uranus
rotates on its side.
Neptune
Neptune is the eighth and farthest-known planet from
the Sun in the Solar System. In the Solar System, it is the
fourth-largest planet by diameter, the third-most-massive
planet, and the densest giant planet.
Neptune has 14 moons. A giant planet, Neptune's
atmosphere is made of hydrogen, helium, and methane.
These components, specifically methane, are what give
the planet its blue color.
Dwarf Planets
Dwarf planets are small planetary-mass object that does not dominate its region
of space and is not a satellite. Dwarf planets don’t have a fixed orbit. So far,
there are 5 reported dwarf planets that exist in our solar system.
83
Asteroid and Asteroid Belts
Asteroids are small, rocky objects that orbit the Sun. Although asteroids orbit the
Sun like planets, they are much smaller than planets. There are lots of asteroids
in our solar system. Most of them are found in the main asteroid belt—a region
between the orbits of Mars and Jupiter.
Asteroids can measure anywhere between a few feet to several hundred miles in
diameter.
Comet
Comets are dirty space snowballs of mostly ice and dust that formed during the
birth of the solar system 4.6 billion years ago. Most comets have stable orbits in
the outer reaches of the solar system past the planet Neptune.
Meteoroids, Meteors, Meteorites
Meteoroids are tiny asteroids or the broken-off crumbs of comets. They range in
size from a grain of sand to 1 meter wide. When meteoroids collide with a planet's
atmosphere, they become meteors. If those meteors survive the atmosphere and
hit the planet's surface, their remains are called meteorites.
84
Exercise:
Let us check what we have learnt:
1) The diagram shows a sun, with a planet and a moon in their orbits.
Draw a straight line from each letter to the correct object.
Letter
A
B
C
Object
sun
planet
moon
2) Pluto was discovered in 1930. It was classified as planet. In 2006, scientist
agreed that Pluto is not a Planet. From the diagram of our solar system given
below, explain what support the idea that Pluto is a planet.
85
3) The table shows information about four planets
The diagram below shows the orbits of the Earth, mercury, Venus and Mars and
their position at one particular time. The arrows show the direction in which the
planets moves.
In the diagram above, show the position of each planet after 6months by
drawing letter X on orbit of each planet
4) Answer the following
a) The Planet which is red in colour b) The planet which has same size as Earth c) The planet that has a year almost twice as long as the Earth’sd) The planet which has biggest size e) The planet that rotates on its side 86
5) The table below gives the distance from the Sun of seven planets. The surface
temperature of each planet is also given in Kelvin (K).
a) Name the planet furthest from the Sun.
______________________________________________________________
b) Venus is the nearest planet to the Earth. Give the distance from Venus to
the Earth.
______________________________________________________________
c) Draw the bar on the graph for the distance of Uranus from the Sun.
d) Write down the temperature difference between Venus and Neptune.
______________________________________________________________
87
e) What happens to the temperature of the planets as they become further away
from the Sun?
______________________________________________________________
f) Amir draws a graph showing the temperature of each planet. One label is
missing. Add the missing label to the graph.
g) One of the bars in his graph is the wrong height. Draw a circle around the bar
that is the wrong height.
88
3.5
Living in space
Space exploration
Space exploration is the use of astronomy and space technology to explore outer
space. While the exploration of space is carried out mainly
by astronomers with telescopes, its physical exploration though is conducted
both by unmanned robotic space probes and human spaceflight. Space
exploration, like its classical form astronomy, is one of the main sources for space
science.
Space exploration has benefited many areas of science and technology including
satellites and GPS. It carries significant risks including radiation, extreme
temperatures and high-speed impacts.
Benefits of space exploration
Many areas of science and technology have made advances due to technological
breakthroughs resulting from the manned exploration of space.
To get into orbit, powerful engines are required to provide thrust and
hence velocity. Survival in space requires excellent environment control systems.
NASA has had to patent many applications to accomplish their tasks. Some
examples include: water filters, ear thermometers, scratch resistant lenses,
memory foam, shoe insoles, long distance communication, smoke detectors,
enriched baby food and cordless tools.
89
Other benefits have included the development of satellites and associated
technologies. With satellites we can communicate with anyone at almost any
point on Earth. We can monitor weather systems to help predict the weather and
we can monitor environmental conditions such as temperature and water
content as well as gravitational field strength and the Earth's magnetic field.
We can also navigate ourselves with GPS (global positioning system). This system
uses 3 satellites at any single time to pinpoint your location but there is a system
of about 35 satellites that help us do this.
Satellites
In space terms, a satellite is generally defined as an object which orbits a planet.
The Moon is Earth's one natural satellite, but we also have thousands of artificial
satellites that have been put into space orbiting the planet.
An artificial satellite orbits the Earth by travelling at a high velocity at a set
distance above the planet. The satellite is attracted by the Earth's gravity and the
manner in which it "falls" enables it to orbits the planet.
One of the most common types of satellite is one that travels around the Earth at
the same rate as the Earth rotates on its axis.
This means that the satellite appears to “hover” above the same point (on the
equator) on the Earth’s surface. A receiver can be pointed at this satellite,
allowing for a link for information to pass to be established. These satellites are
known as “geostationary” and have to be placed at a height of 36,000 km and at
a velocity that means the satellite takes 24 hours to complete one revolution of
the Earth.
Hubble space telescope
90
When a satellite is in a lower orbit, such as a weather satellite, it has to travel at
a greater velocity in order to remain in orbit. On a clear night you can see these
satellite pass by with the naked eye.
Conversely, if a satellite is at a higher orbit it needs to travel at a lower velocity in
order to remain there.
Many aspects of our day-to-day life is dependent upon satellites:

Global Positioning Systems (GPS) allow us to use a phone or other device, such
as a sat nav, to determine our location to within a few metres.

Television networks rely heavily on satellites to transfer signals from one area
to another eg live reporting from major events.

Our weather forecasts are based upon data taken from satellite systems which
have monitored the area around where we live. We can receive very up-to-date
images of clouds and such which are then shown on our forecasts.

Satellites with various detectors and telescopes can observe distant objects and
allow us to analyse them in order to increase our knowledge of the Universe in
which we live. The Hubble space telescope has increased our knowledge of
space a great amount.
Other benefits
Space exploration stimulates the creation of both tangible and intangible benefits
for humanity. Tangible impacts include all the innovation‐related applications and
benefits resulting from investments in these programmes, such as new devices
and services that spin off into the marketplace. In addition, space exploration
leads to advances in science and technology, and furthers workforce
development and industrial capabilities, thus leading to an overall stimulation of
private companies and industries, all of which contributes significantly to the
economic progress of space‐faring nations. Space exploration is also known to
attract young people into careers in science and technology to the general benefit
of society and the economy.
The fundamental benefits generated by space exploration are grouped as follows:
(i) innovation; (ii) culture and inspiration; and (iii) new means to address global
challenges. The delivery of these benefits to society provides the main rationale
for investment in space exploration.
Space exploration’s capacity to continue delivering significant benefits to
humanity was recognized by high‐level government representatives from around
91
the world when they convened in Lucca, Italy, in November 2011. They concluded
that space exploration provides:
Unprecedented opportunities to deliver benefits to humanity on Earth. These
Benefits Stemming from Space Exploration benefits include fueling future
discoveries; addressing global challenges in space and on Earth through the use
of innovative technology; creating global partnerships by sharing challenging and
peaceful goals; inspiring society and especially the younger generations through
collective and individual efforts; and enabling economic expansion and new
business opportunities.
How Space Exploration Delivers Benefits
The benefits of space can be categorized as either direct or indirect. The direct
benefits of exploration include the generation of scientific knowledge, the
diffusion of innovation and creation of markets, the inspiration of people around
the world, and agreements forged between the countries engaged in
exploration.
Indirect benefits that result over time include tangible enhancements to the
quality of life such as improved economic prosperity, health, environmental
quality, safety, and security. They also include intangible philosophical benefits
such as a deepened understanding and new perspectives on humankind’s
individual and collective place in the Universe.
Possibilities for benefit creation multiply rapidly when the products of space
exploration interact with the imagination and creativity present in other fields of
endeavour. Cultural benefits may depend on exploration mission stories and
images spreading broadly across society. Educational organisations, the media
92
and communications industries play a role in interpreting and amplifying
exploration data, so that citizens may understand and appreciate their
significance. To maximize societal impact, space agencies share space exploration
results and collaborate with research institutions, businesses, universities,
schools, museums, and other organizations.
The figure above represents a model of the links between space activities and
ultimate societal benefits, and it helps space agencies explain and assess the
unique contribution that space exploration makes to producing benefits for
humanity.
Exercise:
Q.1. Research and find out the answers for the following questions:
i. What are the 5 main stages of a space missions in regard to visiting planets:
a) _______________________________________________________________
b) _______________________________________________________________
c) _______________________________________________________________
d) _______________________________________________________________
e) _______________________________________________________________
ii. When humans are in space, there tends to be adverse health effects the longer
you are in that environment. What is the main cause of the deterioration
(specifically bone loss) of the body?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
iii. The _______________ are organisms that are able to survive in space due to
their amazing ability to survive in harsh environments.
iv. Name at least two reasons as to why being a human on the surface of Mars
would be difficult:
a) _______________________________________________________________
b) _______________________________________________________________
93
v. What privatized company created the reusable rocket that would allow for
cheaper missions and a reduction on materials for space missions?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
vi. List 3 benefits that space exploration and space research and development
has given to us in modern society:
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
Q.2. Read this article about NASA’s latest high-tech space telescope. Then, have
fun doing one or both of the word puzzles that use the important words in the
article.
TELESCOPE AS TIME MACHINE
If all goes as planned, the National Aeronautics and Space Administration (NASA) has just
launched a new space telescope that will see back in time 80% of the way to the Big Bang. The
Big Bang is the colossal explosion that gave the universe its start around 12 billion years ago
(give or take a few billion years). The Galaxy Evolution Explorer, or GALEX for short, is an Earthorbiting telescope that is looking back 10 billion years to help scientists understand how
galaxies like our Milky Way came to be and how they have changed over cosmic time. During
its 29-month mission, GALEX will survey nearly the entire sky and gather galactic light that has
been journeying toward us for nearly the entire history of the universe.
GALAXIES 101
Galaxies are clusters of gas, dust, many different types of stars in all different phases of their
life cycles, and various strange objects such as black holes. Our own Milky Way galaxy contains
over 200 billion stars, and the entire universe probably contains over 100 billion galaxies.
Galaxies come in a huge variety of shapes and sizes. Dwarf galaxies may contain as few as 10
million stars, while massive galaxies may have a trillion (that’s a thousand billion) stars. Shapes
of galaxies may be spiral, elliptical, or irregular.
Spiral galaxies have a large concentration of stars at the center, called the “bulge,” and “arms”
that extend outward. Viewed face on, they often look like giant pinwheels. The spiral arms are
rich in gas and dust needed to form new stars. Spiral galaxies that are sending out large
amounts of blue and ultraviolet light (more about this kind of light later) tell scientists that
94
many new stars are forming. Our galaxy, the Milky Way, is an average-sized, spiral-shaped
galaxy and is forming new stars at a rate of one star like our Sun every year.
Elliptical galaxies range from spherical to cigar shaped. These galaxies do not contain much gas,
so are rarely seen to be forming new stars. Their red color tells scientists that they contain
mostly old stars. Irregular galaxies don’t have much structure and are generally smaller than
spiral or elliptical galaxies.
BEYOND IMAGINATION’S LIMITS
So how is looking at far away galaxies like looking back in time? At 300,000 kilometers per
second (186,000 miles per second), nothing travels faster than light. Even at this speed, though,
it still takes time for light to get from one place to another. If you are looking at your girlfriend
just across the classroom, you are seeing her as she was a tiny fraction of a second ago, rather
than as she looks right now. It takes about 8 minutes for light from the Sun to reach Earth. The
Voyager 1 spacecraft, which NASA launched back in 1977, is now the farthest human-made
object from Earth. Even though this spacecraft is still inside our solar system, its signal, traveling
at light speed, takes 12 hours to reach Earth!
So, if Voyager’s signal takes that long to reach us, you can begin to imagine how long it takes
light to reach us from far distant galaxies. What we are seeing of those galaxies is not how they
look today, but how they looked when that now-very-old light left them, thousands or millions
or billions of years ago.
DOES THE LIGHT SHOW ITS AGE?
How will scientists know how old the light is that GALEX is receiving?
Scientists know that the universe is expanding. Like a chocolate chip cake in the oven, space is
the “cake batter” that keeps getting bigger and bigger, while the stars and galaxies are the
“chocolate chips” that keep getting farther and farther apart. Like energy pulsing through the
ocean, light energy travels in waves. As light waves travel through this expanding space, they
get stretched out. The longer they spend traveling through space, the more stretched out they
get. Because red light waves are longer than the light waves of other visible colors, scientists
say that light coming from distant stars and galaxies is “red-shifted.” The more red-shifted the
light waves, the farther (and longer) they have traveled. GALEX is able to detect light that is
extremely old, extremely red-shifted.
Like the Hubble Space Telescope that has given us so many awesome pictures of the universe,
GALEX operates above Earth’s atmosphere, so gathers light that cannot penetrate to telescopes
on Earth’s surface. While the Hubble is used by many astronomers around the world to study
very particular, tiny regions of the sky, GALEX has its very specific mission to look at nearly the
whole sky, a goodly piece at a time.
With the “all-sky survey” GALEX is making, scientists will be able to see how galaxies in the early
universe (far, far away) are different from galaxies of more recent times (relatively nearby).
Because distant galaxies appear to us as they were millions or even billions of years ago, we
can study how they evolve. We see what they looked like when the universe was much younger,
as galaxies were first forming. As we look at closer and closer galaxies we see how they change
95
as they age, just as looking at babies, children, teenagers, and then adults can show how we
humans change as we age.
MORE VIOLET THAN VIOLET?
GALEX is paying particular attention to how the universe looks in ultraviolet (UV) light. UV light
waves are not visible to humans. The shortest light waves that humans can see are blue or
violet. Ultraviolet waves, as their names implies, are shorter than violet waves. These shorter
waves carry more energy than do visible light waves (or the light waves that are longer than
those we can see, like infrared and radio waves). Most of the UV light from the Sun is absorbed
or scattered by Earth’s atmosphere, but what does get through to Earth’s surface is what causes
fair-skinned people to get sunburned. GALEX detects ultraviolet objects in the sky that are more
than a million times fainter than objects we can see in visible light from even the darkest
locations on the ground.
What is so special about UV in studying stars and galaxies? The youngest stars are the brightest
and hottest stars, and they produce a lot of UV light. By precisely measuring the brightness of
the UV light coming from a galaxy, scientists can tell how fast that galaxy is churning out new
stars. GALEX’s UV surveys will help scientists measure not only star formation rates, but many
other characteristics of galaxies, such as luminosity (brightness), shape, gas content, how
galaxies cluster together, and how such properties change over cosmic time. We may not be
able to actually place ourselves into the past, but remember: Space is time and time is space.
So to look far back in time, all you need is a good telescope!
GALACTIC PUZZLES
1. EXPLORING THE GALAXIES (CROSSWORD)
Across
1 All there is
3 Nearby star
6 Common to human, octopus, & some galaxies
7 Viewer into the past
9 The blanket above us
12 Our galactic home
16 Another eye in the sky
17 Light gets under your skin
19 The youngest and the _____
21 Like air out in space
24 Amoeba-like galaxy
26 Pinwheel galaxy
29 From where we stand
30 Our closest celestial family
33 How much it shines
35 Much stranger than that of Alice’s rabbit
36 More than blue
96
Down
2 True nothingness
4 Space agency of the U.S
5 Make longer
8 What started the whole thing
10 Opposite of contracting
11 A red star is this
13 A blue star is this
14 Raw material for new stars
15 Light made longer
18 Change over time
20 Age of the universe, times about 12 yrs
22 Great balls of fire
23 Star student
25 Egg-shaped galaxy
27 The farthest artifact
28 Surveying the galaxies
31 Speediest traveler
32 Pulse of energy
34 Lots made where stars are born,
abbreviation
97
2. WORD SEARCH
The words in the list on the left are hidden in the jumble of letters. Words may
be frontwards, backwards, upside-down, or diagonal. When you find a word,
draw a box around it and cross it off the list.
98
3.6
The life cycle of a star
Introduction - Life cycle of a star
Most scientist believe universe was created by big bang 13 billion years ago.
Universe was a hot glowing ball of radiation in first minutes the nuclei of the
lightest elements formed, as universe expanded over millions of years its
temperature fell, uncharred atoms were formed.
A galaxy is a collection of billions of stars held together by their own gravity.
Before galaxies and stars formed the universe was a dark patchy cloud of
hydrogen and helium, then dust and gas were pulled together by gravitational
attraction to form stars. The resulting intense heat in each star started nuclear
fusion reactions so they began to emit visible light and other radiation. The force
of gravity pulled matter into galaxies and stars.
Gravity and nuclear fusion reactions drive the formation and development of
stars. Stars with different masses grow and change throughout the different
stages of their lives. The life cycle for a particular star depends on its size.
Formation of a star
Stars are formed from massive clouds of dust and gas in space. The time they burn
for and their life cycle depend upon their size. Stars are grouped in galaxies. Many
galaxies make up the Universe. Stars are formed from massive clouds of dust and
gas in space.
Gravity pulls the dust and gas together to form a protostar. As the gases come
together, they get hot. A star forms when it is hot enough for nuclear reactions
to start. This releases energy, and keeps the star hot.
During the main sequence period of its life cycle, a star is stable because
the forces in it are balanced. The force of the star’s gravity balances the outward
99
pressure from the expanding hot gases. Our Sun is halfway through its 10 billion
year stable phase.
Gravity pulls smaller amounts of dust and gas together, which form planets in
orbit around the star.
Example - The Sun
The Solar System was formed around 4.6 billion years ago from a large cloud of
dust and gas, called a nebula. This collapsed under its own gravity,
transferring gravitational potential energy to kinetic energy in its particles. As the
nebula collapsed it became denser, and rotated more rapidly. Collisions between
particles caused kinetic energy to be transferred as internal energy and thermal
energy. The core of the nebula began to form a hot, dense protostar.
When the Sun’s core became hot enough and dense enough, nuclear
fusion reactions began, giving out energy and radiation. A star like the Sun is at
equilibrium - gravity tends to pull it inwards, and radiation pressure from the
nuclear reactions tends to expand it outwards. In other words, the gravitational
collapse is balanced by the expansion due to fusion energy.
The Sun is currently a main sequence star and will remain so for another 4-5
billion years. It will then expand and cool to become a red giant, after which it will
shrink and heat up again to become a white dwarf. The white dwarf star will run
out of nuclear fuel and slowly cool down over many billions of years.
All stars begin life in the same way. A cloud of dust and gas, also known as
a nebula, becomes a protostar, which goes on to become a main sequence star.
Following this, stars develop in different ways depending on their size.
Solar Mass Stars (about the same size as the Sun)


All stars form from a giant cloud of hydrogen gas, called a nebula.
As the mass falls together it gets hot. The force of gravity within a nebula pulls
the gas together until it forms a hot ball of gas, known as a protostar.
100

Once the protostar gets hot enough, nuclear reactions start within its core
and it becomes a main sequence star.
The lifecycle of a solar mass star

Solar mass stars have life spans of the order of billions of years.
(The Sun’s lifespan is anticipated to be around 10 billion years – we’re about
half way through it).
 Eventually the Sun will reach a stage when it starts to run out of hydrogen gas
in its core. Once this happens, the nuclear reactions in the core will start to
die down.
 When this happens the core will start to shrink and heat up, starting a new
series of reactions around the core. These will cause the outer part of the Sun
to swell up and it will become a red giant.
 Once this second stage of reactions have finished, the core will collapse
completely, becoming a white dwarf (the hot remnants of a star) whilst the
outer parts will be ejected, forming a spherical cloud of gas around the white
dwarf – a planetary nebula.
Larger Stars (far greater than the Sun in size)

Stars that are larger than the Sun have much shorter lifespans – perhaps in
the region of hundreds of millions of years (instead of billions).
The lifecycle of a star much larger than the Sun
101






When the nuclear fuel in the core of a large star starts to run out, the star will
swell up once again, but this time it will form a much larger star – a red
supergiant.
Once the reactions inside the red supergiant finally finish, the core of the star
will collapse suddenly causing a gigantic explosion – a supernova.
At the centre of this explosion a dense body, called a neutron star will form.
The outer remnants of the star will be cast off into space, forming a nebula.
In the case of the biggest stars, the neutron star that forms at the centre will
continue to collapse under the force of gravity until it forms a black hole.
The term nebula in astronomy refers to any cloud of gas or dust. The nebula
that form stars are made from hydrogen, whilst the ones that are formed
when stars die are made from much heavier elements, such as helium.
Exercise:
1. Draw and describe the different stages of the life cycle of a star about the same
size of Sun.
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
102
2. Label the diagram with all the words given as well as write down the Letter
that matches each object.
1. Black Hole ____
3. Protostar ____
5. Main sequence star____
6. When a star begins to run
out of fuel and grows larger ____
2. Supernova ____
4. Gravity causes this
to condense into a protostar ____
7. Neutron star ____
3. Words from the text have been scrambled in the circles below. Your job is to
unscramble the letters and write the correct word on the line under each circle.
103
104
4. In the list below you will find the steps in the life cycle of a massive star. The
steps are not in order. Using the information, you have learned about massive
stars, place the steps in the order in which they occur in a star’s life cycle.
i. A supernova occurs.
ii. Nuclear fusion occurs which causes the star to glow.
iii. If it is a massive star, a neutron star forms. If it is a super massive star, a
black hole forms.
iv. Gravity pulls hydrogen gas together to form a cloud.
v. Iron, which acts as an energy sponge, forms within the star.
vi. A red giant forms when the star’s hydrogen level drops.
vii. A main sequence star, which can live for millions or even billions of years,
forms.
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
5. Draw a line to connect each word to the group of words that best describes it.
a. Star
The medium size star in our solar system
b. Sun
To shine brightly
c. Core
A star that does not give off light
d. Glow
A glowing ball of gas
e. Red Giant
A giant explosion that took place in
space a very long time ago
f. Expand
The middle
g. Black Dwarf
A large star that glows red
h. Big Bang
To grow larger
105
106