Physics Note! ( Chap. 1&2)

1 ST EXAMINATION

 COVER 2 CHAPTER
 CHAPTER 1& 2

1.2 UNDERSTANDING
BASE QUANTITIES AND
DERIVED QUANTITIES
Physical Quantity

Physical characteristic that can be measured

Base Quantities Derived Quantities

BASE QUANTITY
Quantities that cannot be
defined in terms of other
base quantities (5 only)

DERIVED QUANTITY
Physical quantities derived by combining base
quantities by multiplication, division or both.

1.3 UNDERSTANDING SCALAR
AND VECTOR QUANTITIES
SCALAR QUANTITY VECTOR QUANTITY

Quantities that have Quantities that have
magnitude but no both magnitude and
direction direction

Consistency, Accuracy and
Sensitivity

How to improve accuracy

 Take reading twice or more and the average
value are calculated
 Avoid parallax error
 Avoid zero error
 Use high accuracy measuring instrument

PARALLAX ERROR
It occurs because the position of the eye
is not perpendicular
to the scale of the instrument.

How to avoid parallax error ?

1) To avoid ,position of the eye must be
in line with the reading to be taken
2) To overcome parallax errors in
instruments with a scale and pointer,
e.g. an ammeter it is often useful to
have a mirror behind the pointer.

Vernier Calliper

Main scale

Vernier scale

Vernier Callipers reading
= Main scale + Vernier scale
= 2.7 + 0.06
= 2.76 cm

Read the measurement.
Find the correct reading

Observed Reading = main scale + vernier scale
= (0.4 + 0.09) cm
= 0.49 cm

Corrected reading = observed reading – zero error
= 0.49 – (+ 0.02) cm
= 0.47 cm

Micrometer Screw Gauge

Ratchet Knob =Prevent the user from
exerting too much pressure

Positive zero error

2 divisions below horizontal
reference

Positive Zero error
= + 0.02 mm

Negative zero error

3 divisions above horizontal
reference

Negative Zero
error = - 0.03 mm

PENDULUM EXPERIMENT
Inference The period of a simple pendulum is
depends on its length

Hypothesis The longer is the pendulum
the longer is the period of its
oscillation
Aim To Investigate the relationship
between length and period of a simple
pendulum.
Variable:
Manipulated -Length of the pendulum, l
Responding -Period of the pendulum, T
Fixed -Mass of the pendulum bob, m

List of Retort stand, coin,plasticine
apparatus pendulum bob
and material

coin

Retort stand

pendulum

Procedures 1. Set up the apparatus as shown in the
figure above.
2. Measure the length of the pendulum,l
= 90.0 cm by using a meter rule.
3. The bob of the pendulum was
displaced and released.
4. Time of 20 oscillations is
measured by using a stop watch.
5. Repeat the timing for another 20
oscillations. Calculate the average
time.Period = t oscillations
20
6. Repeat steps 2, 3 and 4 using l =
50.0 cm, 60.0 cm, 70.0 cm and
80.0 cm

IMPORTANT REMINDER
WHEN YOU TABULATE DATA!!

BEWARE WITH…

HOW TO TABULATE DATA

Length of Time taken for 20
pendulum complete Period ,T T2 (s2)
, l(cm) oscillation, t(s) =t /20 (s)
t1 t 2 Mean,t

90.0 1)All data for manipulated and responding
variable must follow the accuracy of the instrument
80.0
70.0 2)mean,t can be calculated using formula
(t1 + t2)/2 .the answer can be 2 or 3 decimal place
60.0
50.0

Responding at second column
(depends on question)
Manipulated at first column

1) Correct symbols and unit !!
Length of Time taken for 20 complete Period , T2 (s2)
pendulum, oscillation, t (s) T
l(cm) =t /20
t1 t2 Average,t
( s)

90.0
80.0
70.0
60.0
50.0

2) Don’t do calculation in the table!
Length of Time taken for 20 complete oscillation, Period ,T=
pendulum t/s (t /20 )s
,l/cm t1 t2 Mean,t
90.0 18.9 19.1 (18.9 + 19.1) 19.0 ÷ 20
2 =0.950
= 19.0
80.0 17.9 17.9 17.9 0.895
70.0 16.8 16.8 16.8 0.840
60.0 15.6 15.6 15.5 0.775
50.0 13.9 14.1 14.0 0.700

3) decimal place must be
consistent column by column!!
Length Time taken for 20 Period , T2 (s2)
of complete oscillation, t/s T
pendulu t1 t2 Mean, =t /20 s
m,L/cm t
90.0 19.1 19 19.0 0.950
80.0 17.9 17.9 17.9 0.895
70.0 16.8 16.8 16.8 0.840
60.0 15.6 15.5 15.5 0.775
50.0 15.6 14.0 14 0.700

Discussion Precautions :
1. Oscillation time is measured
when the pendulum attained a
steady state.
2. Time for 20 oscillations is
repeated twice to increase
accuracy.
Conclusios The period increases when the
length of the pendulum increases.
Therefore, hypothesis accepted.

IMPORTANT REMINDER
WHEN YOU PLOT GRAPH!!

BEWARE WITH…

1)Title of graph must be shown
2) Suitable scale
- scale must start from zero
- cannot skip scale
2) Correct symbols and units
3) Correct plot
4) Smooth line
5)Line passing y-axis (do extrapolation)
6) More than 50% of the graph paper

How to analyze the data
a) determine the relationship between
2 variables

rate of change of rate of change of
distance displacement

ms-1
ms -1

Average of speed = total distance travel,s
(m)
time taken,t (s)
= ms-1

Average of velocity = total displacement,s(m)
time taken,t(s)
= ms-1

Determination of acceleration

u = 3/0.2 = 15.0cms-1
v
v = 8/0.2 = 40.0 cms-1 8

t = (6-1) x 0.2 = 1s 7

6

5
a = v-u 4
u
t 3

= 40.0 – 15.0 2

1
1 0

= 25.0 cms-2

The equation of motion
s : displacement, (m)
u : initial velocity (ms-1)
v : final velocity (ms-1)
a : acceleration(ms-2)
t : time,(s)

5 important formula
(must memorize)
v −u 1 2
a= s = ut + at
t 2

v = u + at v = u + 2as
2 2

1
s = (u + v )t
2

The force acted on the trolley is 120 N. The luggage has a
mass of 20 kg.

(a) What is the weight of the luggage ? [1
mark ]
(b) In the space below draw the components of force 120 N for
[1
mark ]
 (i) Determine the values of the vertical component [ 2 marks ]
 (ii) Calculate the force acted on the ground

EXAMPLES 1:
 An astronaut has a mass of 75 kg.
What is his weight if
 He is on the surface of the Earth
where the gravitational field strength
is 9.8 N kg-1 ?
c) he is on the surface of the Moon
where the gravitational field strength
1
is 6 of that on the surface of the
Earth?

SOLUTION :
a) On the surface of the Earth,
his weight, W = m x g
= 75 x 9.8
= 735 N
 On the surface of the Moon, gravitational field strength, g
= x 9.8 N kg-1
1
his weight, W = 6 x g
m
9 .8
= 75 x
6
= 122.5 N

EXAMPLES 2: (SPM ‘ 03)

The figure shows a marble, a
razor blade and a piece of
paper being released at the
same time in a vacuum
cylinder.
Which object will reach the
base first?

ANSWER 2:
 All three objects will reach the base at
the same time.
( all three objects are falling with the same
gravitational acceleration)

EXAMPLES 3: (SPM ‘ 03)

A stone is dropped from a height of 8 m
above the surface of the Moon. Calculate
the time taken for the stone to reach the
surface of the Moon.
[Moon’s gravitational acceleration = of 1
Earth’s gravitational acceleration] 6
Solution:

1
s = ut + gt2 2

SOLUTION 3:
s = ut +
1 gt2
1 21
8=0+ 2 6X X 9.8 X t2

t = 3.13 s

Answer…
 a) speed is the rate of distance travelled
(1m)
 b)the speed limit is to reduce the
momentum of heavy vehicles to ensure that
they are able to stop within a safe distance
during the accidents

Design toy car
 (ii) Using the suitable physics concepts, you are required to
give some
 suggestions on designing a toy car. Explain
 your suggestions based on the
 following aspects ;
 - density of the toy car parts
 - engine power
 - spring in suspension system
 - size of tyre
 - the designs of the spring

[10 marks]

Modification Explanation
Low density of motorcycle
parts
So that it is lighter
High engine power To produce high
acceleration//
high resultant force
High spring constant // stiffer
spring
So that the spring is stiffer //
motorcycle bounce less // less
vibration
Wide tyre // smooth tyre To increase
stability // to reduce
friction
8
Total

Wish u all,
All the best…
&
Good luck!!!

Physics Note! ( Chap. 1&2)

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Physics Note! ( Chap. 1&2)