CRITICAL THINKING

The Eiffel Tower has a mass
of 10,000,000 kg. A 100:1
scale model of the tower
made from the same material
will have a mass of
(A) 100,000 kg
(B) 10,000 kg
(C) 1,000 kg
(D) 100 kg
(E) 10 kg
(F) 1 kg

The paths crossed for three men
-- A, B, and C -- walking through
woods. It was a cold night. They
decided to light a fire and rest by
it for the night. They set out to
bring some firewood. A came
back with 5 logs of wood, B
brought 3 logs, but C came back
empty-handed. C requested that
they let him rest by the fire and
promised to pay them some
money in the morning. In the
morning C paid them $8. How
should A and B split the money
fairly?
(A) A $7; B $1
(B) A $6; B $2
(C) A $5; B $3
(D) A $4; B $4
(E) None of these

An insect is climbing up a 30 ft.
vertical wall. Starting from the
bottom, the insect climbs up 3 ft.
during the day and slips down 2
ft. during the night. In how many
days will the insect reach the top
of the wall?
(A) 31 days
(B) 30 days
(C) 29 days
(D) 28 days
(E) 27 days
(F) Never

Two trains are moving
toward each other with
speeds of 17 mph and 43
mph. How far apart are they 1
minute before they pass each
other?
(A) 60 miles
(B) 30 miles
(C) 6 miles
(D) 3 miles
(E) 2 miles
(F) 1 mile

Weight of the Flies. The
weight of a closed jar is W
while the flies inside it are
flying around. What will be
the weight of the jar if the
flies settle down inside the
jar?
(A) Equal to W
(B) Less than W
(C) Less than W
INTRODUCTION TO
PHYSICS
NCEA LEVEL 2
PHYSICS BASICS
The physics course is
made up of three main
areas of study
Theory-explain
observations.
Models-help
to
understand
the concepts
Applicationsconcepts are
used to help
solve other
problems
PHYSICAL QUANTITIES
The study of Physics requires us
to measure physical quantities
and UNITS are used to denote
what quantities we are measuring.
There are 7 units for
measurement. Devised by
the Systeme International
d’Unites’.
These are specific units
for specific
measurements.
It is important that
after every
measurement we
place a UNIT to state
what we are
measuring otherwise
the quantity measured
is useless.
SI units are based
on 3 fundamental
quantities
-Mass kg. M.
-Length m. L.
-Time s. T.
Area
=L x L = L²
Velocity
= L / T = LT -1
Energy
= ½ mv ²
= M x ( L/T) ²
=ML²/T² = units joules
Physical quantities & their units
Quantity
Name
Symbol(s)
Length
I, x, y d,
Mass
etc
Time
M, m
Electric
T, t
current
Temperature I
T
Luminous
intensity
I
Amount of
substance
N
SI Unit
Name
metre
kilogram
second
ampere
kelvin
candela
Symbol
m
kg
s
A
K
cd
mole
mol
Often the size of the quantity Physicists
measure is very large or very small. To
help make the numbers easier to use
prefix multipliers are used. You know
it as standard form.
These are mulitples of ten.
You must learn these and be
able to convert from one to the
other.
The standard prefix
multipliers are:
Standard Prefix Multipliers
Power
109
106
103
10-3
10-6
10-9
10-12
Prefix
Symbol
Giga
Mega
Kilo
Milli
Micro
Nano
Pico
If positive power, If negative power,
Is the Greek letter
pronounced
move decimal
move
decimal‘mew’
place
place to the right. to the left
G
M
k
m

n
p
EXAMPLE QUESTIONS
1. Change 8 km to
m
2. How many
micrograms are
there in a
kilogram?
3. Write 2.8x1010
watts in
gigawatts
Solutions:
1. 8 km
= 8 x 103m
= 8000m
2. 1 kg
= 1 x 103g
= 1 x 103 x 106g
= 109g
3. 2.8 x 1010W = 2.8 x 10 x 109W
= 28 x 109W
= 28 GW
SIGNIFICANT FIGURES
Certain pieces of measuring
equipment have limits to how
accurately they can measure
quantities.
This is shown by using specific sig.
figs.
A 30 cm ruler can measure up to
1mm only. Therefore 15.7 cm in
SI units must be written as
0.157m. This measurement is to
3 sig. figs. 0.1570 means you can
measure to less than 1mm, which
you can’t.
Multiplication
or Division
• the measurement
should be the least
number of significant
figures of the data
values used.
Addition or
Subtraction
• the measurement
should be rounded to
the least number of
decimal places of the
data values used.
EXAMPLE:
A metal plate has the
following dimensions:
Length 15.4cm.
Width 0.94cm.
Calculate :
Perimeter of the plate
Area of the plate
SOLUTION
a. Perimeter of the plate:
= 15.4 + 0.94 + 15.4 + 0.94
= 32.68
= 32.7 cm (to 1 decimal point)
b. Area of the plate:
= 15.4 x 0.94
= 14.476
= 14 cm2 (to 2 sf)
EXERCISES
Read through pages 4-9
from Rutter.
4: all
5: 1,2,3
6: 1-4
8: all
9: all
DATA ERROR
As Physicists you now have to
question the validity of the
data you collect. Can you
accept it or should you do it
again.
Two terms that should be
employed when looking at
data are PRECISE and
ACCURATE.
When looking at
error we firstly have
to deal with
whether there is an
error in the first
place.
What do these terms mean:
PRECISE :
cluster of data but possibly in the wrong place.


ACCURATE :
data which is grouped around the right place.


ACCURATE & PRECISE:
data which is clustered in the right place and close
together.


The dictionary definitions of these two words do not clearly
make the distinction as it is used in the science of
measurement.
Accurate means "capable of providing a correct reading or
measurement." In physical science it means 'correct'. A
measurement is accurate if it correctly reflects the size of the
thing being measured.
Precise means "exact, as in performance, execution, or amount.
"In physical science it means "repeatable, reliable, getting the
same measurement each time."
We can never make a perfect measurement. The best we can do
is to come as close as possible within the limitations of the
measuring instruments.
Let's use a model
to demonstrate
the difference.
Suppose you are
aiming at a
target, trying to
hit the bull's eye
(the center of the
target) with each
of five darts.
Here are some
representative
pattern of darts
in the target.
This is a random
like pattern,
neither precise
nor accurate. The
darts are not
clustered together
and are not near
the bull's eye.
This is a
precise
pattern, but
not accurate.
The darts are
clustered
together but
did not hit
the intended
mark.
This is an
accurate
pattern, but
not precise.
The darts
are not
clustered,
but their
'average'
position is
the center of
the bull's
eye.
This pattern is
both precise
and accurate.
The darts are
tightly
clustered and
their average
position is the
center of the
bull's eye.

There are two types of error
1.
Random error - are statistical fluctuations
(in either direction) in the measured data
due to the precision limitations of the
measurement device. Random errors
usually result from the experimenter's
inability to take the same measurement in
exactly the same way to get exact the same
number.
2.
Systematic error - by contrast, are
reproducible inaccuracies that are
consistently in the same direction.
Systematic errors are often due to a
problem which persists throughout the
entire experiment.
Random
Systematic
-measurement just as
-consistently makes the
measurement either
larger or smaller than the
true value
likely to be larger or
smaller than the true
value
Measuring instrument not being
very sensitive. Having to
estimate to the nearest division
on a scale
Calibration error: Incorrectly
adjusted measuring device. E.g
stopwatch that always runs to
fast.
Lack of perfection of the
Zero error: measuring device that
observer.
doesn’t measure zero for zero
E.g. many people timing an event measurement.
with a stopwatch
Random fluctuations in the
object being measured
E.g Light level may vary when
the voltage across a solar cell is
being measured
Parallax error: Incorrect
measuring procedure from
observer. Reading the scale from
an angle is called parallax error.
HOW DO WE IMPROVE THE ACCURACY OF
OUR MEASUREMENT?
1.
Take repeated readings and average them
2.
Take a multiple measurement of some quantity
and then divide by the number of items being
measured
3.
Adjust the zero reading or subtract value from
the readings when using that instrument
4.
Read directly from in front of the scale
Systematic and random errors refer to problems
associated with making measurements. Mistakes made
in the calculations or in reading the instrument are not
considered in error analysis.
It is assumed that the experimenters are careful and
competent!
GRAPHING SKILLS
CONVERTING RELATIONSHIPS TO
EQUATIONS
In order to produce an equation from data the following
steps should be observed:
1.Tabulate your raw data and sketch this on a graph.
2. Decide what relationship has been produced i.e. y  x; y  1/x; y  x2 e.t.c.
3. Do the function to x i.e. if y  1/x then do x-1 to all the x values.
4. Plot y versus 1/x and this should produce a straight line if you have drawn it
correctly.
5. Calculate the gradient of the straight line using the rise/run
method.
6. This is ‘m’ in the ‘y = mx + c’ equation.
7. In most cases ‘c’ = 0 so can be ignored.
8. Rewrite the equation with the function of ‘x’ and the new gradient.
COMMON GRAPHS

yx

y  1/x

y  x²

y  1/x²
Y is proportional to X
 When X changes by certain factor,
Y changes by the same.

Y is inversely proportional to X
 When X is multiplied by a certain factor, Y is divided
by the same factor

Y is proportional to the square of X
 As X is multiplied by a certain factor,
Y is multiplied by the square of that factor

Y is inversely proportional to the square of X
 As X increases by a certain factor, then Y decreases by
1/ the square of that factor
 E.g. X doubled, Y decreases by 1/4

Using these skills do exercises
from
Page: 10 -20
RUTTER