Force and motion for grade 7 IGCSE Cambridge

1. 30/10/2022
30/10/2022
Forces and
Motion
EdExcel iGCSE 9-1 Physics topic 1
W Richards
Education Using
PowerPoint

2. Movement and Position
30/10/2022

3. 30/10/2022
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Distance, Speed
and Time
Speed = distance (in metres)
time (in seconds)
s
t
v
1) Will walks 200 metres in 40 seconds. What is his
speed?
2) Ruby covers 2km in 1,000 seconds. What is her speed?
3) How long would it take Sophie to run 100 metres if she
runs at 10m/s?
4) Aaron runs to the shop to buy Fifa 19 and travels at
50m/s for 20s. How far does he go?
5) Taylor drives her car at 85mph (about 40m/s). How
long does it take her to drive 20km?
5m/s
2m/s
10s
1000m
500s
You are expected to learn this equation!!!

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Distance, Speed
and Time (harder)
Speed = distance (in metres)
time (in seconds)
s
t
v
1) Eliza walks 2000m in 50 minutes. What is her speed in
m/s?
2) Archie tries to walk the same distance at a speed of
5m/s. How long does he take?
3) David drives at 60mph (about 100km/h) for 3 hours. How
far has he gone?
4) The speed of sound in air is 330m/s. Isobel shouts at a
mountain and hears the echo 3 seconds later. How far
away is the mountain? (Careful!)
0.67m/s
400s
300km
495m

5. Speed
30/10/2022
What are the typical speeds for when you walk, run and ride a
bike?
Walking ≈ 1.5m/s
Running ≈ 3m/s
Cycling ≈ 6m/s
What about cars? Aeroplanes?

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Distance-time graphs
40
30
20
10
0
20 40 60 80 100
4) Diagonal line
downwards =
3) Steeper diagonal line =
1) Diagonal line =
2) Horizontal line =
Distance
(metres)
Time/s

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40
30
20
10
0
20 40 60 80 100
1) What is the speed during the first 20 seconds?
2) How far is the object from the start after 60 seconds?
3) What is the speed during the last 40 seconds?
4) When was the object travelling the fastest?
Distance
(metres)
Time/s
0.5m/s
40m
1m/s
40-60s

8. 30/10/2022
40
30
20
10
0
20 40 60 80 100
1) Who was travelling the fastest?
2) Who was travelling the slowest (but still moving)?
3) Who didn’t move?
Distance
(metres)
Time/s
G B
N
Y

9. 30/10/2022
Distance-Time graphs
Task: Produce a distance-time graph for the following
journey:
1) Christina walks 50m in 20 seconds.
2) She then stands still for 10 seconds
3) She then runs away from Luke and covers 100m in 30
seconds.
4) She then stands still and catches her breath for 20
seconds.
5) She then walks back to the start and covers the total 150m
in 50 seconds.

10. 30/10/2022
40
30
20
10
0
20 40 60 80 100
1) What was the velocity in the first 20 seconds?
2) What was the velocity between 20 and 40 seconds?
3) When was this person travelling the fastest?
4) What was the average speed for the first 40 seconds?
Distance
(metres)
Time/s
1.5m/s
0.5m/s
80-100s
1m/s

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30/10/2022
40
30
20
10
0
20 40 60 80 100
1) What is the speed during the first 20 seconds?
2) How far is the object from the start after 50 seconds?
3) What is the speed during the last 40 seconds?
4) When was the object standing still?
Distance
(metres)
Time/s
2m/s
35m
0.25m/s
20-40s

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Acceleration
V-U
T
A
Acceleration = change in speed (in m/s)
(in m/s2) time taken (in s)
1) A cyclist accelerates from 0 to 10m/s in 5 seconds.
What is her acceleration?
2) A ball is dropped and accelerates downwards at a rate of
10m/s2 for 5 seconds. How fast will it be going?
3) A car accelerates from 0 to 20m/s with an acceleration
of 2m/s2. How long did this take?
4) A rocket accelerates from 0m/s to 5,000m/s in 2
seconds. What is its acceleration?
2m/s2
50m/s
10s
2500m/s2
You need to learn this equation!!

13. 30/10/2022
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Acceleration (harder)
V-U
T
A
Acceleration = change in velocity (in m/s)
(in m/s2) time taken (in s)
1) A cyclist slows down from 10 to 0m/s in 5 seconds.
What is her acceleration?
2) A ball is dropped and accelerates downwards at a rate of
10m/s2 for 12 seconds. How much will the ball’s velocity
change by?
3) A car accelerates from 10 to 20m/s with an acceleration
of 2m/s2. How long did this take?
4) A rocket accelerates from 1,000m/s to 5,000m/s in 2
seconds. What is its acceleration?
-2m/s2
120m/s
5s
2000m/s2

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Velocity-time graphs
80
60
40
20
0
10 20 30 40 50
Velocity
m/s
T/s
1) Upwards line =
2) Horizontal line = 3) Upwards line =
4) Downward line =

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80
60
40
20
0
1) How fast was the object going after 10 seconds?
2) What is the acceleration from 20 to 30 seconds?
3) What was the deceleration from 30 to 50s?
4) How far did the object travel altogether?
10 20 30 40 50
Velocity
m/s
T/s
40m/s
2m/s2
3m/s2
1700m

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30/10/2022
80
60
40
20
0
1) How fast was the object going after 10 seconds?
2) What is the acceleration from 20 to 30 seconds?
3) What was the deceleration from 40 to 50s?
4) How far did the object travel altogether?
10 20 30 40 50
Velocity
m/s
T/s
10m/s
4m/s2
6m/s2
1500m

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80
60
40
20
0
10 20 30 40 50
Velocity
m/s
T/s
David runs home to tell someone about his commendation.
This velocity-time graph shows David’s journey to home.
How far away does he live?
2500m

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Acceleration (recap) V-U
T
A
Acceleration = change in velocity (in m/s)
(in m/s2) time taken (in s)
1) Eliza accelerates from standstill to 50m/s in 25 seconds.
What is her acceleration?
2) Hayden accelerates at 5m/s2 for 5 seconds. He started at
10m/s. What is his new speed?
3) Luke is in trouble with the police. He is driving up the A29
and sees a police car and brakes from 50m/s to a standstill.
His deceleration was 10m/s2. How long did he brake for?
4) Archie brakes at the same deceleration but only for 3
seconds. What speed did he slow down to?
2m/s2
35m/s
5s
20m/s

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80
60
40
20
0
10 20 30 40 50
Velocity
m/s
T/s
This velocity-time graph shows Sonny’s journey to school.
How far away does he live?
2200m

20. Another equation of motion
30/10/2022
For a constantly-accelerating body, we can also use this
equation:
v2 = u2 + 2as
You DON’T need to learn this
equation!!
1) An object starts from rest and accelerates at
a rate of 2m/s2 over a distance of 20m. What
is its final velocity?
2) Aaron drives up the M1 and covers 30km. He
started at 2m/s and constantly accelerated
during the whole journey at a rate of
0.001m/s2. What was his final speed?
3) (Harder!) Rachael decelerates from 30 to
10m/s over a distance of 5m. What is her
acceleration?
8.9m/s
8m/s
-80m/s2

21. 30/10/2022
Calculating acceleration using Ticker Tape
1) Find the first “distinct” dot and draw a line through it:
2) Count 5 gaps (=5/50ths or 1/10th of a second) and draw another line:
3) Repeat for every tenth of a second:
4) Cut the strips out and stick them next
to each other onto graph paper:

22. 30/10/2022
Calculating acceleration using Ticker Tape
Your graphs will look like this:
Speed down a 10cm slope
0.1 0.2 0.3 0.4 0.5
0
1
2
3
4
5
Time/s
Speed/
cm/0.1s
To calculate the acceleration
you need to follow 3 easy steps:
1) Work out the START and END
speeds:
Start speed = 1cm/0.1s = 10cm/s
End speed = 5cm/0.1s = 50cm/s
2) Work out the time taken:
Time taken = 0.5 - 0.1 = 0.4s
3) Calculate the acceleration:
A = (50 – 10) / 0.4 = 100cm/s2
V-U
T
A

23. Forces, Movement, Shape
and Momentum
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24. The Effect of Forces
30/10/2022
What are forces doing in each of the following situations?

25. 30/10/2022
What is a force?
Forces are usually gravitational or electrostatic. Some examples:
________ – pulls
things downwards
(gravitational)
___ ________ (drag) – acts against
anything moving through air (electrostatic)
______ – keeps things afloat
(electrostatic)
_____ – acts against anything
moving (electrostatic)
Words – upthrust, air resistance, friction, weight

26. 30/10/2022
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Speed vs. Velocity
Speed is simply how fast you are travelling…
Velocity is “speed in a given direction”…
This car is travelling at a
speed of 20m/s
This car is travelling at a
velocity of 20m/s east

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Circular Motion
1) Is this car travelling at constant speed?
2) Is this car travelling at constant velocity?

28. 30/10/2022
Vector vs. scalar
Scalar quantities have size (“magnitude”) only and no direction.
Vector quantities have both size and direction.
Scalar or vector???
Scalar Vector
1. Mass
2. Distance
4. Speed
5. Velocity
6. Energy
8. Power
7. Time
9. Force
3. Acceleration

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Balanced and unbalanced forces
Consider a camel standing on a road.
What forces are acting on it?
Weight
Reaction
These two forces would be equal –
we say that they are BALANCED.
The camel doesn’t move anywhere.

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Balanced and unbalanced forces
What would happen if we took the
road away?
Weight
Reaction
There is a “resultant force” which
causes the camel to accelerate
downwards (the same direction as
the force).

31. 30/10/2022
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Balanced and unbalanced forces
Predict what these cars will do and explain why:

32. 30/10/2022
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Balanced and unbalanced forces
1) This animal is either
________ or moving
with _______ _____…
4) This animal is also
either _______ or moving
with ________ ______..
2) This animal is getting
________…
3) This animal is getting
_______….
Words - Stationary, faster, slower or constant speed?

33. 30/10/2022
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Summary
If an object is stationary and has NO resultant force on it the object
will…
If an object is stationary and a resultant force acts on it the object will…
If an object is already moving and NO resultant force acts on it the
object will…
If an object is already moving and a resultant force acts on it the object
will…
Complete these sentences…
…continue to stay stationary …accelerate in the direction of the
resultant force
…continue to move at the same
speed and the same direction
…accelerate in the direction of the
resultant force

34. 30/10/2022
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Resultant Force
A “resultant force” is a single force that can replace all of the
other forces acting on something. Calculate and draw the
resultant force of the following:
500N 100N
700N 600N
700N 700N
200N
800N 800N
100N
50N

35. 30/10/2022
30/10/2022
Force and acceleration
If the forces acting on an object
are unbalanced then the object will
accelerate, like these wrestlers:
Force (in N) = Mass (in kg) x Acceleration (in m/s2)
F
A
M
You need to learn this
equation!!

36. 30/10/2022
30/10/2022
Force, mass and acceleration
1) A force of 1000N is applied to push
a mass of 500kg. How quickly does
it accelerate?
2) A force of 3000N acts on a car to
make it accelerate by 1.5m/s2. How
heavy is the car?
3) A car accelerates at a rate of
5m/s2. If it weighs 500kg how
much driving force is the engine
applying?
4) A force of 10N is applied by a boy
while lifting a 20kg mass. How
much does it accelerate by?
F
A
M
2m/s2
2000kg
2500N
0.5m/s2

37. 30/10/2022
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Weight vs. Mass
Earth’s Gravitational Field Strength is 10N/kg. In other
words, a 1kg mass is pulled downwards by a force of 10N.
W
g
M
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
1) What is the weight on Earth of a book with mass 2kg?
2) What is the weight on Earth of an apple with mass 100g?
3) David weighs 700N on the Earth. What is his mass?
4) On the moon the gravitational field strength is 1.6N/kg.
What will David weigh if he stands on the moon?
20N
1N
70kg
112N
You need to learn this equation!!

38. 30/10/2022
30/10/2022
Stopping a car…
What two things must the driver of the car do in order to stop
in time?

39. 30/10/2022
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Stopping a car…
Braking
distance
Thinking
distance
(reaction time)

40. 30/10/2022
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Stopping a car…
Braking
distance
Too much
alcohol
Thinking
distance
(reaction time)
Tiredness
Too many
drugs
Wet roads
Driving too
fast
Tyres/brakes
worn out
Icy roads
Poor
visibility
Total Stopping Distance = Thinking Distance + Braking Distance

41. Stopping Distances
30/10/2022

42. 30/10/2022
Terminal Velocity
Some questions to consider:
Consider a ball falling through a liquid:
1) What forces are acting on
the ball?
2) How do those forces
change when the ball gets
faster?
3) Will the ball keep getting
faster? Explain your
answer in terms of forces

43. 30/10/2022
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Terminal Velocity
Consider a skydiver:
1) At the start of his jump the air
resistance is _______ so he
_______ downwards.
2) As his speed increases his air
resistance will _______
3) Eventually the air resistance will be
big enough to _______ the
skydiver’s weight. At this point
the forces are balanced so his
speed becomes ________ - this is
called TERMINAL VELOCITY
Words – increase, small,
constant, balance, accelerates

44. 30/10/2022
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Terminal Velocity
Consider a skydiver:
4) When he opens his parachute the
air resistance suddenly ________,
causing him to start _____ ____.
5) Because he is slowing down his air
resistance will _______ again until
it balances his _________. The
skydiver has now reached a new,
lower ________ _______.
Words – slowing down, decrease,
increases, terminal velocity, weight

45. 30/10/2022
30/10/2022
Velocity-time graph for terminal velocity
Velocity
Time
Speed
increases…
Terminal
velocity
reached…
Parachute opens –
diver slows down
New, lower terminal
velocity reached
Diver hits the ground

46. 30/10/2022
Force and Extension
Consider a mass on a spring:
When a force is applied to
this spring it will change
shape and extend.
What happens when a mass is
added?

47. 30/10/2022
Investigating Force and Extension
Task: Find an expression that
relates extension to the
amount of weight added.
Force is proportional to
extension – “Hooke’s Law”
Weight added
(N)
Extension (cm)
1
2
3
4
5
6

48. 30/10/2022
Force-Extension Graph for a spring
Force/N
Extension/mm
The “limit of
proportionality”.
Force is proportional to extension as long as
you don’t go past the “limit of
proportionality”. There is a linear
relationship up to here – the object has
obeyed Hooke’s Law up to this point.

49. 30/10/2022
Elastic and Inelastic Deformation
Force/N
Extension/mm
If you don’t use too much force
on the spring you can take the
force off and the spring returns
to its original shape – this is
“elastic deformation”.
If you put too much force on the
spring it “stretches” – in other
words, when you remove the
force the spring does not go
back to its original length. This
is “inelastic deformation”.

50. 30/10/2022
Force-Extension Graph for a wire
Force/N
Extension/mm
The “elastic limit”
“Permanent deformation”
The “plastic
region”
The “limit of
proportionality”

51. 30/10/2022
Force-Extension Graph for rubber
Force/N
Extension/mm

52. 30/10/2022
30/10/2022
Momentum
Any object that has both mass and
velocity has MOMENTUM. Momentum
(symbol “p”) is simply given by the formula:
Momentum = Mass x Velocity
(in kgm/s) (in kg) (in m/s)
P
V
M
What is the momentum of the following?
1) Archie (mass 50kg) running at 10m/s
2) A 1000kg car travelling at 30m/s
3) A 0.02kg pen thrown across the room at 5m/s
4) Mr Richards (mass 90kg) bungee jumping and
falling at 40m/s
500kgm/s
30,000kgm/s
0.1kgm/s
3600kgm/s
You need to learn this equation!!

53. 30/10/2022
30/10/2022
Conservation of Momentum
In any collision or explosion momentum is conserved (provided that there
are no external forces have an effect). Example question:
Two cars are racing around the M25. Car A collides with the back of car B
and the cars stick together. What speed do they move at after the
collision?
Mass = 1000kg Mass = 800kg
Speed = 50m/s Speed = 20m/s
Momentum before = momentum after…
…so 1000 x 50 + 800 x 20 = 1800 x V…
…V = 36.7m/s
Mass = 1800kg Speed = ??m/s

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Momentum in different directions
What happens if the bodies are moving in opposite directions?
Speed = 50m/s
Mass = 1000kg
Speed = 20m/s
Mass = 800kg
Momentum is a VECTOR quantity, so the momentum of the
second car is negative…
Total momentum = 1000 x 50 – 800 x 20 = 34000 kgm/s
Speed after collision = 34000 kgm/s / 1800 = 18.9m/s

55. 30/10/2022
30/10/2022
More questions…
1. A car of mass 1000kg heading up the M1 at 50m/s collides
with a stationary truck of mass 8000kg and sticks to it.
What velocity does the wreckage move forward at?
2. A defender running away from a goalkeeper at 5m/s is hit
in the back of his head by the goal kick. The ball stops
dead and the player’s speed increases to 5.5m/s. If the
ball had a mass of 500g and the player had a mass of 70kg
how fast was the ball moving?
3. A white snooker ball moving at 5m/s strikes a red ball and
pots it. Both balls have a mass of 1kg. If the white ball
continued in the same direction at 2m/s what was the
velocity of the red ball?
4. A gun has a recoil speed of 2m/s when firing. If the gun
has a mass of 2kg and the bullet has a mass of 10g what
speed does the bullet come out at?
5.6m/s
70m/s
400m/s
3m/s

56. 30/10/2022
30/10/2022
Recap question on momentum
1. Milton and Aaron are racing against each other over 400m
at Sports Day. Milton is running at 8m/s and catches up
with Aaron who is running at 6m/s. After the collision
Milton stops and Aaron moves slightly faster. If Milton’s
mass is 60kg and Aaron’s is 70kg calculate how fast Aaron
moves after the collision.
2. Lilian is driving her 5kg toy car around. It is travelling at
10m/s when it hits the back of Christina’s (stationary) leg
and sticks to it. Assuming Christina’s leg can move freely
and has a mass of 10kg calculate how fast it will move after
the collision.
12.9m/s
3.3m/s

57. 30/10/2022
30/10/2022
An extension question using
standard form
Consider the nuclear decay of Americium-241:
Am
241
95
α
4
2
If the new neptunium atom moves away at
a speed of 5x105 m/s what was the speed
of the alpha particle?
Np
237
93
2.96x107 m/s

58. 30/10/2022
Change in Momentum and Force
Instead of F=ma Newton actually said that the force acting on
an object is that object’s rate of change of momentum. In
other words…
mv-mu
T
F
Force = Change in momentum
Time
(in N)
(in kgm/s)
(in s)
For example, Luke scores from a free kick by kicking a stationary football
with a force of 40N. If the ball has a mass of 0.5kg and his foot is in
contact with the ball for 0.1s calculate:
1) The change in momentum of the ball (its impulse),
2) The speed the ball moves away with
You DON’T need to learn this
equation!!

59. 30/10/2022
Example questions
1) Archie likes playing golf. He strikes a golf ball with a
force of 80N. If the ball has a mass of 200g and the
club is in contact with it for 0.2s calculate a) the change
in momentum of the golf ball, b) its speed.
2) Aaron thinks it’s funny to hit tennis balls at David. He
strikes a serve with a force of 30N. If the ball has a
mass of 250g and the racket is in contact with it for
0.15s calculate the ball’s change in momentum and its
speed.
3) Ruby takes a dropkick by kicking a 0.4kg rugby ball away
at 10m/s. If her foot was in contact with the ball for
0.1 seconds calculate the force she applied to the ball.
4) Taylor strikes a 200g golf ball away at 50m/s. If she
applied a force of 50N calculate how long her club was in
contact with the ball for.
16kgm/s,
80m/s
4.5kgm/s,
18m/s
0.2s
40N

60. 30/10/2022
30/10/2022
Safety features
How do air bags and crumple zones work?
Basically:
1) The change in momentum is the same with or without an
airbag
2) But having an airbag increases the time of the collision
3) Therefore the force is reduced

61. 30/10/2022
Newton 1642-1727
Newton’s 1st Law of Motion
Basically, a body will remain at rest or
continue to move with constant velocity as
long as the forces acting on it are balanced.
An unbalanced forwards
force will make me
accelerate…
…and an unbalanced
backwards force will make
me slow down…

62. 30/10/2022
Newton’s 2nd Law of Motion
Newton 1642-1727
The acceleration of a body is proportional to
the resultant force causing its acceleration
and is in the same direction.
In other words…
force = mass x acceleration F
A
M

63. 30/10/2022
Newton’s 3rd Law of Motion
Newton 1642-1727
When body A exerts a force on body B, body
B exerts an equal and opposite force on body
A.
My third law says
that if I push to
the right I will
move backwards
as well.

64. 30/10/2022
Newton’s 3rd Law of Motion
What will happen if I push
this satellite away from me?

65. Newton’s Laws Project
30/10/2022
Task: Create a 2-3 minute presentation on Newton’s 3 Laws, to
include:
1) A clear description of each law
2) A demonstration of it in action

66. 30/10/2022
Balanced or unbalanced?

67. 30/10/2022
Turning Moments
A moment is a “turning force”, e.g. trying to open or close a
door or using a spanner. The size of the moment is given by:
Moment (in Nm) = force (in N) x PERPENDICULAR distance
from pivot (in m)
Calculate the following turning moments:
100 Newtons
5 metres
200 Newtons
2 metres
You need to learn this equation!!

68. 30/10/2022
Turning Moments
100 Newtons
200 Newtons
2 metres 2 metres
Total ANTI-CLOCKWISE
turning moment = 200x2 =
400Nm
Total CLOCKWISE turning
moment = 100x2 = 200Nm
The anti-clockwise moment is bigger so the seesaw will
turn anti-clockwise

69. 30/10/2022
An example question
5 metres
2000 Newtons 800 Newtons
? metres

70. 30/10/2022
Calculate the missing quantity
The following are all balanced:
2N
4m 2m
??N
5N 3N
2m ??m
4m
??m
2m
5N 5N 15N

71. 30/10/2022
1m
A hard question…
Consider a man walking along a plank of wood on a cliff.
3m
Man’s weight =
800N
Plank’s weight =
200N
How far can he walk over the cliff before the plank tips over?
Aaarrgghh

72. 30/10/2022
A recap question
Calculate the mass of man in the example given below:
30kg
1.2m
0.4m

73. Centre of Gravity
30/10/2022
The weight of an object always acts through the object’s
centre of gravity.
Where is the centre of gravity for these objects?

74. 30/10/2022
Driving along a bridge
Consider a car on a suspension bridge:
As the car drives along the bridge, how would the upwards
force on each beam change?
Upwards force =
???
Upwards force =
???

75. 30/10/2022
Extension – calculating the force
To find out what the size of the force is, take moments about
a pivot at the base of the supports:
Weight of bridge
= 500,000N
Weight of car =
10,000N
20m
3m