Physics Module Form 4
2.1
Chapter 2 – Forces & Motion
GCKL 2011
LINEAR MOTIONs
Physical Quantity
Definition, Quantity, Symbol and unit
Distance, s
Distance is the ……
Quantity: …
Displacement, s
SI unit : ..
(a) The distance in .. ….
(b) the distance between ….
….direction.
(c) The distance of its final …..
specified ….
Quantity:
SI unit:
Speed is the
Speed,v
Speed =
Quantity:
SI unit:
Velocity is the
Velocity, v
Velocity =
Direction of velocity is
Quantity :
Average speed
Average velocity
SI unit:
v=
Example: A car moves at an average
speed / velocity of 20 ms -1
On average, the car moves a distance/
displacement of
v
Displacement
TotalTime
2-1
Physics Module Form 4
Chapter 2 – Forces & Motion
Uniform speed
Speed that remains the same in
Uniform velocity
Velocity that remains
An object has a nonuniform velocity if
(a) The direction of motion changes or the motion is not linear.
Acceleration, a
When the velocity of an object
v u
t
Acceleration is defined as the
a
GCKL 2011
(b) The magnitude of its velocity changes.
Change in velocity
Time taken
Final velocity,v - Initial velocity,u
=
Time taken,t
Acceleration=
Unit: ms-2
Acceleration is positive
The velocity of an object increases from an initial velocity, u, to a higher final
velocity, v
Deceleration
acceleration is negative.
The rate of decrease in speed in a specified direction.
Zero acceleration
An object moving at a constants velocity, that is,
Constant acceleration
Velocity increases at a uniform rate.
When a car moves at a constant or uniform acceleration of 5 ms -2, its velocity
1. Constant =
2. increasing velocity =
3. decreasing velocity =
4. zero velocity =
5. negative velocity = object moves at opposite direction
6. zero acceleration =
7. negative acceleration = deceleration
2-2
Physics Module Form 4
Chapter 2 – Forces & Motion
Comparisons between distance and displacement
Distance
Total path length
travelled from
one location to
another
Displacement
The distance between
two locations
measured along the
shortest path
connecting them in
specific direction
GCKL 2011
Comparisons between speed and velocity
Speed
The rate of change of
distance
Scalar quantity
Velocity
The rate of change of
displacement
Vector quantity
Scalar quantity
It has magnitude but no
direction
SI unit
SI unit :
Fill in the blanks:
1. A steady speed of 10 ms -1 = A distance of __________________________________________
2. A steady velocity of -10 ms -1 = A displacement of _________________________________
3. A steady acceleration of 4 ms -2 = Speed _____________________________________________
4. A steady deceleration of 4 ms -2 = ____________________________________________________________
5. A steady velocity of 10 ms -1 = A displacement of 10 m is travelled every 1 second to the right.
2-3
Physics Module Form 4
Chapter 2 – Forces & Motion
Example 1
Every day Rahim walks from his house to the junction
which is 1.5km from his house.
Then he turns back and stops at warung Pak Din which is
0.5 km from his house.
GCKL 2011
Example 2
Every morning Amirul walks to Ahmad’s house
which is situated 80 m to the east of Amirul’s house.
They then walk towards their school which is 60 m
to the south of Ahmad’s house.
(a) What is the distance travelled by Amirul and his
displacement from his house?
(b) If the total time taken by Amirul to travel from
his house to Ahmad’s house and then to school
is 15 minutes, what is his speed and velocity?
Speed =
(a) What is Rahim’s displacement from his house,
• when he reaches the junction.
Velocity =
•
when he is at warung Pak Din.
(b) After, Rahim walks back to his house. breakfast
When he reaches home,
(i) What is the total distance travelled by
Rahim?
(ii) What is Rahim’s total displacement from
his house?
Example 3
Salim running in a race covers 60 m in 12 s.
(a) What is his speed in ms-1
Example 4
An aeroplane flies towards the north with a
velocity 300 km hr -1 in one hour. Then, the plane
moves to the east with the velocity 400 km hr -1 in
one hour.
(b) If he takes 40 s to complete the race, what is his
distance covered?
(a) What is the average speed of the plane?
(b) What is the average velocity of the plane?
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Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
(c) What is the difference between average speed
and average velocity of the plane?
Example 5
The speedometer reading for a car travelling due north
shows 80 km hr -1. Another car travelling at 80 km hr -1
towards south. Is the speed of both cars same? Is the
velocity of both cars same?
A ticker timer
 Use:
 1 tick = time interval
 The time taken to make 50 ticks on the ticker tape is 1 second. Hence, the time interval between 2
consecutive dots is
 1 tick =
2-5
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Relating displacement, velocity, acceleration and time using ticker tape.
VELOCITY
FORMULA
Time, t = 10 dicks x 0.02 s
= 0.2 s
displacement, s = x cm
velocity =
ACCELERATION
Initial velocity, u =
final velocity, v =
acceleration, a =
Elapsed time, t = (5 – 1) x 0.2 s = 0.8 s or
t = (50 – 10) ticks x 0.02 s = 0.8 s
TICKER TAPE AND CHARTS
TYPE OF MOTION
 Distance between the dots increases uniformly

2-6
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
- Distance between the dots decrease uniformly
Example 6
The diagram above shows a ticker tape chart for a
moving trolley. The frequency of the ticker-timer
used is 50 Hz. Each section has 10 dots-spacing.
(a) What is the time between two dots?
(b) What is the time for one strips?
(c) What is the initial velocity?
(d) What is the final velocity?
(e) What is the time interval to change from initial
velocity to final velocity?
(f) What is the acceleration of the object?
a=
vu
t
2
THE EQUATIONS OF MOTION
v  u  at
1
s  ut  at 2
2
2
2
v  u  2as
u=
v=
t=
s=
a=
2-7
Physics Module Form 4
2.2
Chapter 2 – Forces & Motion
GCKL 2011
MOTION GRAPHS
DISPLACEMENT – TIME GRAPH
Velocity is obtained from
A – B : gradient of the graph is
B – C : gradient of the graph =
object is
C – D : gradient of the graph
The object
VELOCITY-TIME GRAPH
Area below graph
Positive gradient
Negative gradient
Zero gradient
GRAPH
s versus t
v versus t
Zero
velocity
Negative
constant
velocity
Positive
Constant
velocity
2-8
a versus t
Physics Module Form 4
GRAPH
Chapter 2 – Forces & Motion
s versus t
GCKL 2011
v versus t
a versus t
Constant
acceleration
Constant
deceleration
Example 1:
Example 2:
velocity/ m s-1
20
10
0
10
20
30
40
time/
s
Based on the s-t graph above:
(a) Calculate the velocity at
(i) AB
(ii) BC
(iii) CD
(a) Calculate the acceleration at:
(ii) JK
(ii) KL
(iii) LM
(b) Describe the motion of the object at:
(i) AB
(ii) BC
(iii) CD
(b) Describe the motion of the object at:
(ii) JK
(ii) KL
(iii) LM
(c) Find
(i) total distance
(c) Calculate
(iii) The total displacement
(ii) total displacement
(iv) The average velocity
(d) Calculate
(i) The average speed
(ii) The average velocity of the
moving particle
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Physics Module Form 4
2.3
Chapter 2 – Forces & Motion
GCKL 2011
INERTIA
Inertia
The inertia of an object is the tendency of the object
Newton’s first law
Every object
Relation between inertia
and mass
The larger the mass,
SITUATIONS INVOLVING INERTIA
SITUATION
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EXPLANATION
EEEEEEEEJNVJLKN
When the cardboard is pulled away quickly, the coin drops straight into
DNFLJKVNDFLKJNB
the glass.
VJKL;DFN BLK;XC
NB[F
NDPnDSFJ[POJDE]OJBD]AOP[FKBOP[DF
LMB NOPGFMB
LKFGNKLB
FGNMNKL’ MCVL
Chilli sauce in the bottle can be BNM’CXLB
easily poured out if the bottle is moved
down fast with a suddenNFGNKEPLANATION
stop. The sauce inside the bottle moves
together with the bottle.
When the bottle stops suddenly,
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Body moves forward when the car stops suddenly The passengers were in a
state of motion when the car was moving.
When the car stopped suddenly,
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A boy runs away from a cow in a zig zag motion. The cow has a large inertia
2-10
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
 The head of hammer is secured tightly to its handle by
knocking one end of the handle, held vertically, on a hard
surface.
This causes the hammer head to continue on its
downward motion
when the handle has been stopped, so that the top
end of the handle is slotted deeper into the hammer
head.
• The drop of water on a wet umbrella will fall when the
boy rotates the umbrella.
• This is because the drop of water on the surface of the
umbrella moves simultaneously as the umbrella is rotated.
•
Ways to reduce the negative
effects of inertia
When the umbrella stops rotating, the inertia of
the drop of water will continue to maintain its
motion.
1. Safety in a car:
(a)Safety belt secure the driver to their seats.
When the car stops suddenly, the seat belt provides
the external force that prevents the driver from
being thrown forward.
(b)Headrest to prevent injuries to the neck during rearend collisions. The inertia of the head tends to
keep in its state of rest when
the body is moved suddenly.
(c)An air bag is fitted inside the steering wheel.
It provides a cushion to prevent the driver from
hitting the steering wheel or dashboard during a
collision.
2. Furniture carried by a lorry normally are tied up together by
string.
When the lorry starts to move suddenly, the furniture are
more difficult to fall off due to their inertia because
their combined mass has increased.
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Physics Module Form 4
Chapter 2 – Forces & Motion
•
Relationship between mass
and inertia
•
•
•
GCKL 2011
Two empty buckets which are hung with rope from the
ceiling.
One bucket is filled with sand while the other bucket is
empty.
Then, both pails are pushed.
It is found that
Push and compared to the bucket with sand.
• The bucket filled with sand offers more resistance to
movement.
• When both buckets are oscillating and an attempt is made
to stop them, the bucket filled with sand offers

2-12
Physics Module Form 4
2.4
Chapter 2 – Forces & Motion
GCKL 2011
MOMENTUM
Definition
Momentum =
SI unit:
Principle of
Conservation of
Momentum
In the absence of an external force,
Elastic Collision
Inelastic collision
ƒ
Both objects move
ƒ The two objects
ƒ
ƒ
Momentum
Kinetic energy
Total energy
ƒ
ƒ
ƒ
Momentum
Kinetic energy.
Total energy
Total Momentum Before =
Total Momentum Before =
m1 u1 + m2 u2 = ( m1 + m2 ) v
m1u1 + m2u2 = m1 v1 + m2 v2
Explosion
Before explosion both object
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Total Momentum
before collision is
zero
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Total Momentum after
collision :
m1v1 + m2v2
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
From the law of conservation of momentum:
Total Momentum = Total Momentum
Before collision
after collision
0 = m1v1 + m2v2
m1v1 = - m2v2
Negative sign means
EXAMPLES OF EXPLOSION (Principle Of Conservation Of Momentum)
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When a rifle is fired, the bullet of mass m,
moves with a high velocity, v. This creates a
momentum in the forward direction.
From the principle of conservation of
momentum,
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Application in the jet engine:
The launching of rocket
Mixture of hydrogen and oxygen fuels
These high speed hot gases produce
By conservation of momentum,
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Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Paste a picture
In a swamp area, a fan boat is used.
The fan produces a high speed movement of air
backward. This produces a large momentum
backward.
By conservation of momentum, an equal but opposite
momentum is produced and acted on the boat. So the
boat will move forward.
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A squid propels by expelling water at high velocity.
Water enters through a large opening and exits
through a small tube. The water is forced out at a
high speed backward.
Total Mom. before= Total Mom. after
0 =Mom water + Mom squid
0 = mwvw + msvs
-mwvw = msvs
The magnitude of the momentum of water and
squid are equal but opposite direction.
This causes the quid to jet forward.
Example
Example
Before collision
MA = 4 kg
MB = 2 kg
UA = 10 ms -1 r i g h t
UB = 8 ms -1 l e f t
Car A of mass 1000 kg moving at 20 ms -1
collides with a car B of mass 1200 kg moving at
10 m s -1 in same direction. If the car B is
shunted forwards at 15 m s -1 by the impact,
what is the velocity, v, of the car A immediately
after the crash?
Calculate the value of VA .
2-15
After collision
VB 4 ms-1 right
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Example
Example
A truck of mass 1200 kg moving at
30 ms-1 collides with a car of mass
1000 kg which is travelling in the opposite
direction at 20 ms-1. After the collision, the two
vehicles move together. What is the velocity of
both vehicles immediately after collision?
A man fires a pistol which has a mass of 1.5 kg.
If the mass of the bullet is 10 g and it reaches a
velocity of 300 ms -1 after shooting, what is the
recoil velocity of the pistol?
2-16
Physics Module Form 4
2.5
Chapter 2 – Forces & Motion
GCKL 2011
FORCE
Balanced Force
When the forces acting on an object are
balanced,
Example:
Effect : the object
[velocity
]
or
moves
[a= ]
Unbalanced Force/ Resultant Force
When the forces acting on an object are not balanced,
there must be
The net force is known as
Weight, W = Lift, U
Thrust, F = drag, G
Effect : Can cause a body to
-
Newton’s Second Law of Motion
The acceleration produced by a force on an object is
Force = Mass x Acceleration
F = ma
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Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Experiment to Find The Relationship between Force, Mass & Acceleration
a& F
Relationship
between
Situation
a&
m
Both men are pushing the same mass
but man A puts greater effort. So he
moves faster.
Inference
The acceleration produced by an
object depends on the net force
applied to it.
Hypothesis
The acceleration of the object
increases when the force applied
increases
Variables:
Manipulated :
Responding :
Constant :
Apparatus and
Material
Both men exerted the same strength.
But man B moves faster than man A.
Force
Acceleration
Mass
Ticker tape and elastic cords, ticker timer, trolleys, power supply and friction
compensated runway and meter ruler.
2-18
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Procedure :
- Controlling
manipulated
variables.
An elastic cord is hooked over the
trolley. The elastic cord is stretched
until the end of the trolley. The
trolley is pulled down the runway
with the elastic cord being kept
stretched by the same amount of
force
An elastic cord is hooked over a
trolley.
-Controlling
responding
variables.
Determine the acceleration by
analyzing the ticker tape.
Acceleration
Determine the acceleration by analyzing
the ticker tape.
Acceleration
Repeating
experiment.
Tabulation of
data
v u
a
t
Repeat the experiment by using two
, three, four and five elastic cords
Force, F/No of
elastic cord
1
2
3
4
5
Acceleration a 
Repeat the experiment by
Acceleration, a/ ms-2 Mass, m/
no of
trolleys
1
2
3
4
5
Analysing
Result
2-19
v u
t
Mass,
m/g
1/m,
g-1
Acceleration/
ms-2
Physics Module Form 4
Chapter 2 – Forces & Motion
1. What force is required to move
2 a 2 kg object
with an acceleration of 3 m s- , if
(a) the object is on a smooth surface?
(b) The object is on a surface where the
average force of friction acting on the
object is 2 N?
3. A car of mass 1200 kg travelling at 20 ms -1
is brought to rest over a distance of 30 m.
Find
(a) the average deceleration,
(b) the average braking force.
2-20
GCKL 2011
2. Ali applies a force of 50 N to move a 10 kg
table at a constant velocity. What is the
frictional force acting on the table?
4. Which of the following systems will
produce maximum acceleration?
Physics Module Form 4
2.6
Chapter 2 – Forces & Motion
GCKL 2011
IMPULSE AND IMPULSIVE FORCE
Impulse
The change of
Unit :
Impulsive Force
m=
u =
v =
t=
The rate of change
change of momentum mv  mu

time
t
Unit =
Impulsive force
is
Effect of time
Longer period of time →Impulsive force
Shorter period of time →
Situations for Reducing Impulsive Force in Sports
Situations
Explanation
Thick mattress with soft surfaces are used in events such as high jump
so that
Goal keepers will wear gloves to
A high jumper will bend his legs upon landing. This is to
so as to
A baseball player must catch the ball in the direction of the motion of
the ball. Moving his hand backwards when catching the ball prolongs
the time for the momentum to change so as to reduce the impulsive
force.
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Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Situation of Increasing Impulsive Force
Situations
Explanation
A karate expert can break a thick wooden slab with his bare hand
that moves at a very fast speed. The short impact time results in
A massive hammer head moving at a fast speed is brought to rest
upon hitting the nail within a short time interval.
A football must have enough air pressure in it so
Pestle and mortar are made of stone. When a pestle is used to pound
chillies the hard surfaces of both the pestle and mortar cause the pestle
to be stopped in a very short time. A large impulsive force is resulted
and thus causes these spices to be crushed easily.
Example 1
A 60 kg resident jumps from the first floor of a burning house.
His velocity just before landing on the ground is 6 ms-1.
(a) Calculate the impulse when his legs hit the ground.
(b) What is the impulsive force on the resident’s legs if he
bends upon landing and takes 0.5s to stop?
(c) What is the impulsive force on the resident’s legs if
he does not bend and stops in 0.05 s?
(d) What is the advantage of bending his legs upon landing?
Example 2
Rooney kicks a ball with a force of 1500 N. The time of
contact of his boot with the ball is 0.01 s. What is the impulse
delivered to the ball? If the mass of the ball is 0.5 kg, what is
the velocity of the ball?
2-22
Physics Module Form 4
2.7
Chapter 2 – Forces & Motion
GCKL 2011
SAFETY VEHICLE
Safety features in vehicles
Component
Function
Headrest
Air bag
Windscreen
Crumple zone
Front
bumper
ABS
Absorb the shock from the accident. Made from steel, aluminium, plastic or
rubber.
Enables drivers to quickly stop the car without causing the brakes to lock.
Side impact bar
Seat belt
2-23
Physics Module Form 4
2.8
Chapter 2 – Forces & Motion
GCKL 2011
GRAVITY
Gravitational
Force
Objects fall because they are
This force is known as the
The earth’s gravitational force
Free fall

An object is falling freely when it is falling under the force of gravity
only.


An object falls freely only


In vacuum,
They fall with
 Objects dropped
Acceleration due to
gravity, g

Gravitational field
The gravitational field is the region around the earth in which an object
experiences a force towards the centre of the earth. This force is the
gravitational attraction between the object and the earth.
The gravitational field strength is defined as the gravitational force which acts
on a mass of 1 kilogram.
g=
F
m
-1
Its unit is N kg .
2-24
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
-1
Gravitational field strength, g = 10 N kg
-2
Acceleration due to gravity, g = 10 m s
The approximate value of g can therefore be written either as
-1
or as 10 N kg .
Weight
Comparison
between weight
&
mass
10 m s
-2
The gravitational force acting on the object.
Weight = mass x gravitational acceleration
W = mg
SI unit : Newton, N and it is a vector quantity
Mass
The mass of an object is the
amount of matter in the object
Weight
The weight of an object is the force of
gravity acting on the object.
Constant everywhere
Varies with the magnitude of gravitational
field strength, g of the location
A scalar quantity
A base quantity
A vector quantity
A derived quantity
SI unit: kg
SI unit : Newton, N
The difference
between a
fall in air and
a free fall in a vacuum
of a coin and a
feather.
Both the coin and the
feather are released
simultaneously from
the same height.
At vacuum state: There is no air
resistance.
The coin and the feather will fall
freely.
Only gravitational force
acted on the objects. Both will fall
at the same time.
2-25
At normal state: Both coin and feather
will fall because of gravitational force.
Air resistance effected by the surface area of
a fallen object.
The feather that has large area will have
more air resistance.
The coin will fall at first.
Physics Module Form 4
Chapter 2 – Forces & Motion
(a) The two spheres are falling
with an acceleration.
The distance between two
successive images of the sphere
increases showing that the two
spheres are falling with increasing
velocity; falling with an
acceleration.
GCKL 2011
The two spheres are falling down with
the same acceleration
The two spheres are at the same level
at all times. Thus, a heavy object and
a light object fall with the same
gravitational acceleration
Gravitational acceleration is
independent of mass
Two steel spheres
are falling under
gravity. The two
spheres are dropped
at the same time
from the same
height.
Motion graph for free fall object
Free fall object
Object thrown upward
Example 1
A coconut takes 2.0 s to fall to the ground. What
is
(a) its speed when it strikes the ground
(b) ) the height of the coconut tree
2-26
Object thrown upward and fall
Physics Module Form 4
2.9
Chapter 2 – Forces & Motion
GCKL 2011
FORCES IN EQUILIBRIUM
Forces in
Equilibrium
When an object is in equilibrium,
rd
Newton’s 3 Law
Examples( Label the forces acted on the objects)
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Resultant
A single force that
Force
Addition of Forces
Resultant force, F =
+
Resultant force, F =
+
2-27
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Two forces acting at a point at an angle [Parallelogram method]
STEP 1 : Using ruler and protractor, draw
the two forces F1 and F2 from a point.
STEP 3
Draw the diagonal of the parallelogram. The
diagonal represent the resultant force, F in
magnitude and direction.
STEP 2
Complete the parallelogram
scale: 1 cm = ……
Resolution of Forces
A force F can be resolved into components
which are perpendicular to each other:
(a) horizontal component , FX
(b) vertical component, FY
Inclined Plane
Fx = F cos θ
Component of weight parallel to the plane = mg sin θ
Component of weight normal to the plane = mg cos θ
Fy = F sin θ
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Physics Module Form 4
Chapter 2 – Forces & Motion
Find the resultant force
(d)
(e)
2-29
GCKL 2011
Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Lift
Stationary Lift
Lift accelerate upward
Lift accelerate downward
Resultant Force =
Resultant Force =
Resultant Force =
The reading of weighing
scale =
The reading of weighing
scale =
The reading of weighing
scale =
Pulley
1. Find the resultant force, F
2. Find the moving mass, m
3. Find the acceleration, a
4. Find string tension, T
2-30
Physics Module Form 4
2.10
Chapter 2 – Forces & Motion
GCKL 2011
WORK, ENERGY, POWER & EFFICIENCY
Work
Work done is
W = Fs
W=
,F=
s=
The SI unit of work is the joule, J
1 joule of work is done when
The displacement, s of the object is in the direction of the force, F
The displacement , s of the
object is not in the direction of
the force, F
W = Fs
s
F
W= F s
Example 1
A boy pushing his bicycle with a
force of 25 N through a distance
of 3 m.
Calculate the work done by the
boy.
Example 2
A girl is lifting up a 3 kg
flower pot steadily to a height
of 0.4 m.
What is the work done by the
girl?
2-31
Example 3
A man is pulling a crate of fish
along theW
floor
a force
of
= (Fwith
cos θ)
s
40 N through a distance of 6 m.
What is the work done
in pulling the crate?
Physics Module Form 4
Concept
Power
Energy
Chapter 2 – Forces & Motion
D
efwork is
The rate at which
in
done,or
iti
on


Formula & Unit
P=
W
t
p = power, W = work / energy
t = time
Energy is the capacity to do work.
Potential Energy
Gravitational potential energy is
the energy of an object due to
its higher position in the
gravitational field.
Kinetic Energy
GCKL 2011
Kinetic energy is the energy of an
object due to its motion.
m=
h=
g=
E=
m=
v=
E=
No work is done when:
A waiter is carrying a tray of
food. The direction of motion of
the object is perpendicular to
that of the applied force.
A waiter is carrying a tray of
food and2-32
walking
No force is applied on the object
in the direction of displacement
(the object moves because of its
own inertia)
A satellite orbiting in space.
There is no friction in space. No
force is acting in the direction of
movement of the satellite.
Physics Module Form 4
Principle of Conservation of
Energy
Chapter 2 – Forces & Motion
GCKL 2011
Energy can be changed from one form to another, but it cannot
be created or destroyed.
The energy can be transformed from
Example 4
A worker is pulling a wooden block of weight, W, with a force
of P along a frictionless plank at height of h. The distance
travelled by the block is x. Calculate the work done by the
worker to pull the block.
Example 5
A student of mass m is climbing
up a flight of stairs which has
the height of h. He takes t
seconds..
What is the power of the student?
Example 6
A stone is thrown upward with
initial velocity of
-1
20 ms . What is the maximum
height which can be reached by
the stone?
Example 7
A ball is released from point A of height
0.8 m so that it can roll along a curve frictionless track. What is the
velocity of the ball when it reaches point B?
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Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Example 8
A trolley is released from rest at
point X along a frictionless track.
What is the velocity of the trolley at
point Y?
Example 9
A ball moves upwards along a
frictionless track of height 1.5 m
-1
with a velocity of 6 ms . What is
its velocity at point B?
Example 10
A boy of mass 20 kg sits at the top of a concrete slide of height 2.5 m. When he slides down the
slope, he does work to overcome friction of 140 J. What is his velocity at the end of the slope?
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Physics Module Form 4
2.11
Chapter 2 – Forces & Motion
ELASTICITY
Elasticity
A property of matter that enables an object
No external force is applied.
Molecules are at their equilibrium separation.
Intermolecular force is equal zero.
Compressing a solid causes its molecules
Repulsive intermolecular force
Stretching a solid
Its molecules are
Stretching a wire by an external
force:
When the external force is removed:
 The attractive intermolecular forces
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GCKL 2011
Physics Module Form 4
Hooke’s Law
Chapter 2 – Forces & Motion
The extension of a spring
F= k x
Force extension graph
GCKL 2011
where
F=
x=
k=
Based on the graph:
Relationship between F & x :
The gradient of the graph represent =
Area under the graph
2
= elastic potential energy = ½ F x = ½ k x
The elastic limit of a spring
The maximum force that
If a force stretches a spring beyond its elastic limit, the spring
Force constant of the spring, k
The force required to produce one unit of extension of the
spring.
k is a measurement of the stiffness of the spring
 The spring with a larger force constant is
 A spring with a smaller force constant is
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Physics Module Form 4
Factors that effect elasticity
Factor
Length
Chapter 2 – Forces & Motion
Change in factor
GCKL 2011
How does it affects the elasticity
Shorter spring
Longer spring
Diameter of spring wire
Smaller diameter
Larger diameter
Diameter spring
Smaller diameter
Larger diameter
Type of material
Springs made of different materials
Elasticity changes according to the type of material
Arrangement of the spring
In series
The same load is applied to each spring.
Tension in each spring = W Extension of
each spring = x
Total extension = 2x
If n springs are used: The total
extension = n x
In parallel
The load is shared equally among the springs.
W
Tension in each spring =
2
x
Extension of each spring =
2
If n springs are used:
The total extension =
Example 1
The original length of each
spring is 10 cm.
With a load of 10 g, the extension
of each spring is 2 cm.
What is the length of the spring
system for (a),
(b) and (c)?
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x
n
Physics Module Form 4
Chapter 2 – Forces & Motion
Example 2
GCKL 2011
Using the diagram shown and the
information given about the weight of
the two objects,
Diagram below represent a
50 cent coin and a leaf falling
in a vacuum container.
The coin is heavier than the
leaf.
compare the mass of the coin and the
leaf, the time taken to fall, the position
of the coin and the leaf and
finally deduce the physical quantity
which causes the objects to fall.
coin
leaf
Mass
of the taken
coin to fall in a vacuum
Time
Position of the coin and the leaf
Coin and leaf of different mass reach the bottom of the container at the same time.
Coin and leaf fall down due to gravitational force. The magnitude of gravitational pull is constant.
It does not depend on the mass
Example 3
Diagram 10 shows a student trying to launch a water rocket.
You are required to give suggestion on how to design a water rocket for National
Competition. Based on your knowledge on forces, motion and properties of materials,
explain your suggestion based on the following aspect:
(i)
material used
(ii)
shape of the rocket
(iii)
suitable angle to launch the rocket
(iv)
volume of water in the rocket
(v)
added structure for the motion of the rocket
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Physics Module Form 4
Chapter 2 – Forces & Motion
GCKL 2011
Water Rocket
Aspect
Structure
Acceration of the Rocket
Make from light material
Structure of the Rocket
Aerodynamic
Upthrust force
Fill with erated water or gasy
drink with water
Stability of the rocket during flight
Use plasticine to make the head
of the rocket
Explanation
Add fins at the back portion of
the rocket
Example 4
Diagram 4.1 shows a cradle with a baby in it is oscillating vertically. Diagram 4.2
shows another identical cradle with a heavier baby in it is oscillating vertically. It
is observed that the cradle with a heavier mass baby oscillates at a higher
frequency.
Design an experiment to test the hypothesis using spring, slotted weight and other
suitable apparatus.
4 (a)
Inference : The extension of the spring depends
1
(b)
c (i)
Hypothesis : As the
1
Aim : To investigate the relationship between
1
Variables :
2-59
Physics Module Form 4
c(ii)
Chapter 2 – Forces & Motion
GCKL 2011
1
Manipulated variable :
Responding variable :
c(iii)
Constant variable :
1
Apparatus : Metre rule, retort stand with clamp ,steel spring, slotted weight and
pin.
1
Set-up the apparatus
1
c(iv)
c (v)
Method of controlling the manipulated variables :
1
1. Arrangement the apparatus as shown in the diagram.
2.Mark the initial
Method of measuring the responding variables :
Record
1
Extension of spring :
Measure the
Repeat the
1
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Physics Module Form 4
c ( vi)
Chapter 2 – Forces & Motion
GCKL 2011
1
Tabulate Results
Initial length , l0 =
cm
Mass of the Slotted weight , m / g
40
80
120
160
200
Weight of slotted mass / N
0.4
0.8
1.2
1.6
2.0
Length of the spring ,l / cm
Extension of the spring x = l- l0
(vii)
1
Total
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12