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KS4 Further Forces
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Ticker timers
A ticker timer is used as an accurate timing device
for motion experiments.Ticker timers print dots on
paper at a rate of 50 dots per second.
This means the distance between two dots is
equivalent to 1/50th of a second or 0.02 seconds.
How much time is shown here?
7/50th of a second or
0.14 seconds
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Describe the motion for the ticker tape shown:
Accelerating/decelerating/constant velocity
Accelerating/decelerating/constant velocity
Accelerating/decelerating/constant velocity
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Plastic
Example?
Plasticene
If you put a force on an object making the object change
shape and it stays the same shape after you remove the force
we say the object is plastic.
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Elastic
Example?
A spring
If you put a force on an object making the object change
shape and it returns to its original shape after you
remove the force we say the object is elastic.
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Elastic and plastic
Write down four examples of plastic and elastic materials.
Elastic
Plastic
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Match the force with its definition:
Tension
The force on a material
when it is being
squashed.
Compression
The force on a material
when it is being
stretched.
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Tension or compression?
T – Tension
C - Compression
T
Your triceps muscle when you bend your arm.
C
T
A fishing line holding a fish.
C
T
A football being kicked.
C
T
A string holding a conker.
C
T
Pushing in a syringe.
C
T
An arrow in a bow.
C
T
Your biceps muscle when you bend your arm.
C
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Standing on a plank:
Where is the plank being compressed?
Where is the plank being stretched?
What force pulls down on the man?
Tension
Compression
Gravity
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Stretching springs
What do you predict will happen as masses are attached to a spring?
1.
Attach a spring to a stand.
2. Record the length of the spring using a ruler.
3. Add a 50g mass to the spring.
4. Record the new length of the spring.
5. Continue to add masses to the spring up to
500g in total.
6. Plot a graph of load against extension.
7. What do your results tell you?
Mass
(g)
Load
(N)
Length
(cm)
Extension
(cm)
0
0
2.4
0
50
0.5
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Load and extension for a metal spring
Extension
(cm)
Plastic region
Elastic limit
Load  extension
Load (N)
What do we call the point after which the
The Elastic Limit
spring
Where
Where
will
isthe
load
notgraph
return
proportional
isto
a its
straight
original
to extension?
line.
shape?
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How are mass, force and acceleration
related?
Two masses
of 1 kg and 4
kg are both
subject to the
same force,
which one will
accelerate the
fastest?
The lower the mass, the greater the acceleration for a specific force.
This is why Grand Prix cars get faster as they use up their fuel.
Less fuel, means less mass, less mass means greater acceleration.
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F=ma
We can express the relationship between force, mass
and acceleration using the equation:
Force = mass x acceleration
F =ma
Force measured in Newtons (N)
Mass measured in kilograms (kg)
Acceleration measured in metres per second per second (ms-2)
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Formula triangles
Formula triangles help you to rearrange formula. The
triangle for the f=ma formula is shown below:
Whatever quantity you are trying to find, cover it up
and it will leave you with the calculation required.
…and you are left
with the sum…
So if you were
trying to find mass,
m…..
…you would
cover m up…

F
m
a

m = F
a
x
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Force calculations:
1. What force will make a mass of 4 kg accelerate at 5
ms-2?
Force = 20 N
2. A force of 50N acts on a 2 kg mass. What will be
the acceleration of the mass?
Acceleration = 25 ms-2
3. A force of 2 000N accelerates a car at 2.5 ms-2.
What is the mass of the car?
Mass = 800 kg
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Force questions:
1. Label the forces acting upon a moving bike.
B
A - Thrust
C
B - Reaction
A
D
C – Air resistance
E
D - Friction

E - Gravity
2. Fill in the table:
A > (C+D)
Bike accelerating
Bike at steady speed
Bike decelerating

A
=(C+D)

A<
(C+D)

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Turning forces
Two masses on a see-saw.
What force acts on the masses?
Which way will the see-saw go?
gravity
pivot
gravity
The see-saw turns around the pivot.
What factors effect the size of a turning force?
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Moments
The size of the turning force or moment depends
upon:
1. The distance of the force from the pivot.
2. The size of the force.
Moment = Force x perpendicular distance from pivot
Moments measured in Newton metres (Nm)
Force measured in Newtons (N)
Distance measured in metres (m)
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Principle of moments
Anticlockwise moments = Clockwise moments
2m
25N
1m
50N
Where should a force of 50N be
positioned to balance the see-saw?
Anti-clockwise
moments
25NNxxClockwise
m
moments
Clockwise
moments
==50
?2m
50 Nm = 50 N
Nm
x?M
distance
=1m
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Principle of moments
Drag and drop any of the masses onto the “see – saw” and try to get it to
balance. The masses are in kilograms and the distance in metres.
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Moments questions
1. Where should a force of 60N be positioned to balance
the ruler below?
4m
15N
1m
60N
2. What size force should be positioned on the left to
balance the ruler shown?
1m
Force = 60 N
?N
4m
15N
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Pressure
Forces are pushes, pulls and twist.
Pressure is a measure of how spread out a force is.
As you in increase the size of the force you increase the
size of the pressure.
Less
pressure
More
pressure
As you increase the size of the area over which a force
acts, you decrease the pressure.
More
pressure
Less
pressure
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Pressure questions
1. Why do tractors have such large tyres?
The tyres have a large area so that the weight of
the tractor is spread over a large area.
This reduces the pressure the tractor puts on
the ground, so that it doesn’t sink into the mud.
2. Why would a lady in stiletto heels standing on your foot hurt you
more than a elephant standing on your foot?
The elephant has a greater weight than the lady and it would have
a greater pressure if the area the weight acted upon was the
same.
However, the lady’s weight is concentrated into a smaller area
than that of the elephant’s. This means that the stiletto heel exerts
a greater pressure than the foot of the elephant, and might hurt
more.
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P=F/A
We can express the pressure formula using the
equation:
Pressure = Force ÷ Area
P =F/A
Pressure measured in pascals (Pa)
Force measured in newtons (N)
Area measured in metres squared (m2)
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Hydraulics
We can use the fact that the pressure in a liquid is the same at
any point to make a machine that magnifies force.
Comment on the area of the plungers, the relative distance
travelled and the energy input/output.
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Formula triangles
Formula triangles help you to rearrange formula.
The triangle for the pressure formula is shown below:
Whatever quantity you are trying to find, cover it up
and it will leave you with the calculation required.
So if you were
trying to find
pressure, P…..
…you would
cover P
up…
…and you are left
with the sum…

F
P
A

P = F
A
x
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The pressure you put on the ground during
a handstand:
1. Put your hand on a piece of
graph paper.
2. Count the number of 1cm2
squares your hand covers.
3. Multiply this number by two
(you have two hands).
4. Measure your weight in
Newtons on some scales.
5. Use the pressure formula to
calculate the pressure you
put on the ground.
P=F/A
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Pressure calculations:
1. What pressure will a force of 20N acting over an
area of 4 ms-2 put upon the ground?
Pressure = 5 Pa
2. A force of 50N acts on an area and creates a
pressure of 1.0Pa. Over what area is the force
acting?
Area = 50 m2
3. A pressure of 6 000 Pa is created by a force acting
on an area of at 5 m2. What is the size of the
force?
Force = 30 000 N
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Pressure experiment
A fluid is a liquid or a gas. Get a tin can and drill three holes in
the side, then fill it with water.
What do you observe?
What does this tell you about the pressure in fluids?
The water is forced out a greater
distance as you move down the tin
can. This is because the pressure is
greatest at the bottom - pressure in
fluids increases with depth.
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Why are the walls of a dam wider at the
bottom than at the top?
A. It is cheaper to build
B. Gravity increases with depth
C. Pressure increases with depth 
D. Looks nice
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A pressure of 600 Pa acts over an area of 2m2.
What force creates this pressure?
A. 1 200 N

B. 300 N
C. 1 200 Pa
D. 300 Pa
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Why are racing cars able to travel faster as a
race progresses?
A. The engine has cooled down
B. The petrol has warmed up
C. There is less petrol to accelerate 
D. There is more petrol to accelerate
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