1. OCR Additional Science
22/04/2017
OCR Additional Science
P3 Forces for Transport
AGAC

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

3. Distance, Speed and Time
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Distance, Speed and Time d t S
Speed = distance (in m)
time (in s)
(in m/s)
Dave walks 20 metres in 4 seconds. What is his speed?
Laura covers 12m in 3 seconds. What is her speed?
How long would it take to run 100 metres if you run at 10m/s
Steve travels at 50m/s for 20s. How far does he go?
Susan drives her car at 40m/s. How long does it take her to drive 200m? 5
m/s 4
m/s 10 s
1000 m 5 s

4. Distance-time graphs 2) Horizontal line = 40 30 20 10
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2) Horizontal line = 40 30 20 10
4) Diagonal line downwards =
Not moving
Constant speed…
back to start
Distance
(metres)
3) Steeper diagonal line =
Time/s
Diagonal line =
Constant speed
Faster constant speed

5. 40 30 20 10
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s x t
Distance
(metres)
Time/s
10/2=
5m/s
What is the speed during the first 2 seconds?
How far is the object from the start after 6 seconds?
What is the speed during the last 4 seconds?
When was the object travelling the fastest?
40m
40/4=
10m/s
4 to 6 seconds

6. Distance-time graph for non-uniform motion
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Object is accelerating up to here 40 30 20 10
Object is now decelerating
Distance
(metres)
Time/s

7. Acceleration v-u t a Acceleration = change in velocity (in m/s)
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Acceleration
v-u t a
Acceleration = change in velocity (in m/s)
(in m/s2) time taken (in s)
A cyclist accelerates from 0 to 10m/s in 5 seconds. What is her acceleration?
A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by?
A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take?
A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration?
10/5=
2m/s2
10x12=
120m/s
10/2= 5s
4000/2=
2000m/s2

8. Velocity-time graphs 1) Upwards line = 80 60 40 20
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1) Upwards line = 80 60 40 20
constant acceleration
4) Downward line =
constant deceleration
Velocity
m/s
3) Upwards line =
2) Horizontal line =
T/s
constant velocity
constant acceleration

9. 80 60 40 20 v a x t ½ x 10 x 20= clue: it’s the area under the graph!
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a x t
½ x 10 x 20=
clue: it’s the area
under the graph!
Velocity
m/s
10 x 40=
½ x 20 x 60=
½ x 10x40 =
T/s
10 x 40=
40m/s
How fast was the object going after 10 seconds?
What is the acceleration from 20 to 30 seconds?
What was the deceleration from 30 to 50s?
How far did the object travel altogether?
2m/s2
-3m/s2
200m +
400m +
400m +
100m +
600m =
1700m

10. Speed-time graph for non-uniform motion
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Object’s acceleration is increasing 40 30 20 10
Object’s acceleration is decreasing
Distance
(metres)
Time/s

11. What is a force?
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A force is a “push” or a “pull”. Some common examples:
___ ________ (drag) – acts against anything moving through air
________ – pulls things downwards
_____ – acts against anything moving
______ – keeps things afloat
Words –
upthrust
Air resistance
friction
weight

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

13. Balanced and unbalanced forces
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Reaction
What would happen if we took the road away?
Weight

14. Balanced and unbalanced forces
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What would happen if we took the road away?
The camel’s weight is no longer balanced by anything, so the camel falls downwards…

15. The bigger the arrow, the bigger the force
Air Resistance
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Air resistance is a force that opposes motion through air. The quicker you travel, the bigger the air resistance:
The bigger the arrow, the bigger the force
The same applies to a body falling through a liquid (called “drag” or “upthrust”).

16. Examples of Air Resistance
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Examples of Air Resistance

17. Balanced and unbalanced forces 1
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In each of these
situations the
car is not moving
before each force is
applied
car accelerates
car accelerates
car does not move
car accelerates

18. Balanced and unbalanced forces 2
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Stage 1
car accelerates
Car starting off
Stage 2…
continuing
from stage 1
(moving)
car still
accelerates
but not as
much as in
Stage 1
Next slide for stage 3

19. Balanced and unbalanced forces 2
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Stage 3…
continuing from
Stage 2 (moving)
Car moves at a
steady speed
Now see the next slide
To see how this can be
Put into a graph …..
Stage 4…
continuing from
Stage 3 (moving)
Car
decelerates

20. Balanced and unbalanced forces
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Velocity
constant
speed
accelerating
decelerating
accelerating
Stage 1
Stage 2
Stage 3
Stage 4
Time

21. Balanced and unbalanced forces
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1) This animal is either ________ or moving with _____ _____…
2) This animal is getting _________…
stationary
faster
constant speed
3) This animal is getting _______….
4) This animal is…
slower
stationary

22. Force and acceleration
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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

23. Force, mass and acceleration
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A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate?
A force of 3000N acts on a car to make it accelerate by 1.5m/s2. What mass has the car?
A car accelerates at a rate of 5m/s2. If it has a mass of 500kg how much driving force is the engine applying?
A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by?
1000 =
500
2m/s2 F A M
3000=
1.5
2000Kg
500 x 5 =
2500N
10 = 20
0.5 m/s2

24. Stopping a car… = + Tiredness Too much alcohol Thinking distance
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The following factors
INCREASE distances
Tiredness
Too much alcohol
Thinking distance
Too many drugs
Poor visibility = +
Stopping distance
Thinking distance
Braking distance
Wet roads
Icy roads
Braking distance
Tyres/brakes worn out
Driving too fast

25. Car Safety Features Seat belts Air bags Rigid cage Paddle controls
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Seat belts
Air bags
Rigid cage
Paddle controls
Crumple zone

26. Work Done
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Each Worker needs to do the same amount of work in lifting these boxes on to the shelves 3 2 A B C A B C 1

27. lifts 4 boxes on to the 1st shelf
Work Done
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Worker A
lifts 4 boxes on to the 1st shelf 2 A B C A B C A A A A 1

28. lifts 2 boxes on to the 2nd shelf
Work Done
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Worker B
lifts 2 boxes on to the 2nd shelf B B 2 A B C A B C A A A A 1

29. lifts 1 box on to the 4th shelf
Work Done
Worker C
lifts 1 box on to the 4th shelf
22/04/2017 C 4 3 B B 2 A B C A B C A A A A 1

30. “height” = distance moved
Work Done
No. of boxes x height
1 x 4 = 4
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“box” = weight or force
“height” = distance moved 3
No. of boxes x height
2 x 2 = 4 B B 2 A B C
No. of boxes x height
4 x 1 = 4 A B C A A A A 1

31. Work done = Force x distance moved
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When any object is moved around work will need to be done on it to get it to move (obviously).
We can work out the amount of work done in moving an object using the formula:
Work done = Force x distance moved
in J in N in m W D F

32. Example questions
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Bori pushes a book 5m along the table with a force of 5N. He gets tired and decides to call it a day. How much work did he do?
Alicia lifts a laptop 2m into the air with a force of 10N. How much work does she do?
Martin does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it?
Chris cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use?
Carl drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do?
25J
20J 4m
50N J

33. In other words, 1 Watt = 1 Joule per second
Work and Power
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The POWER RATING of an appliance is simply how much work it does (i.e. how much energy it transfers) every second.
In other words, 1 Watt = 1 Joule per second W T P
W = Work done (in joules)
P = Power (in watts)
T = Time (in seconds)

34. Some example questions
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What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds?
What is the power of an electric fire that transfers 10,000J of energy in 5 seconds?
Isobel runs up the stairs in 5 seconds. If she transfers 1,000,000J of energy in this time what is his power rating?
60W
2000W W

35. Kinetic energy = ½ x mass x velocity squared
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Any object that moves will have kinetic energy.
The amount of kinetic energy an object has can be found using the formula:
Kinetic energy = ½ x mass x velocity squared
in J in kg in m/s
KE = ½ mv2

36. Example questions KE =1/2mv2
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Emily drives her car at a speed of 2m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy?
2) Max rides his bike at a speed of 10m/s. If the combined mass of Max and his bike is 80kg what is his kinetic energy?
KE =1/2 mv2
KE = 0.5 x 1000 x (2)2
KE = 2000 J
KE =1/2 mv2
KE = 0.5 x 80 x (10)2
KE = 4000 J

37. Terminal Velocity Consider a skydiver:
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Consider a skydiver:
At the start of his jump the air resistance is _______ so he _______ downwards.
small
accelerates
2) As his speed increases his air resistance will _______
increase
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
equal
constant
Words – increase, small, constant, equal, accelerates

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

39. Velocity-time graph for terminal velocity…
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Parachute opens – diver slows down
Velocity
Speed increases…
Terminal velocity reached…
No air resistance !
On the Moon
Diver hits the ground
New, lower terminal velocity reached
Time

40. Gravitational Potential Energy
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To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation…
GPE = Mass x Acceleration of free-fall x Change in height
(Joules) (newtons) (=10N/kg) (metres)

41. Gravitational Potential Energy
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To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation…
GPE = Mass x gravitational field strength x Change in height
On Earth g = 10N/kg. This means that every kilogram on Earth experiences a downwards weight of 10N
(Joules) (kg) (N/kg) (metres)
Now let us
consider
an earlier
problem….
GPE h g m

42. Work Done GPE= mxgxh C 1x10x4=40J In this example the work done
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GPE= mxgxh C
1x10x4=40J
In this example the work done
produces an increase in potential
energy 4 3
GPE= mxgxh B B
2x10x2 = 40J 2
GPE= mxgxh A B C
4x10x1 = 40J A A A A 1
Each box has a mass of 1Kg and the shelves are 1m apart
Each worker has transferred 40J into GPE for the boxes

43. Example questions mxgxh 3. GPE=70x10x50= 35000J 1. GPE = 1x10x10= 100J
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GPE
mxgxh
How much gravitational potential energy have the following objects gained?:
A brick that has a mass of 1kg and is lifted to the top of a house (10m),
A 1,000kg car lifted by a ramp up to a height of 2m,
A 70kg person lifted up 50m by a ski lift.
How much GPE have the following objects lost?:
4. A 0.2kg football dropping out of the air after being kicked up 30m,
5. A 50g egg falling from a nest 10m above the ground
6. A 1,000kg car falling off its 2m ramp.
3. GPE=70x10x50= 35000J
1. GPE = 1x10x10= 100J
2. GPE=1000x10x2= J J
5. 5J J

44. Roller Coasters
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1) Electrical energy is transferred into gravitational potential energy
3) Kinetic energy is transferred back into gravitational potential energy
2) Gravitational potential energy is transferred into kinetic energy