1. P2 Higher Revision
- The harder bits

2. speed = distance / time taken
acceleration = change in speed / time taken
force = mass × acceleration
work done = force × distance
power = work done / time
kinetic energy = ½ mv2
Gravitational potential energy = mgh
weight = mass × gravitational field strength
Momentum = mass x velocity
Force = change in momentum / time
Force on a spring = spring constant x extension
Energy = 0.5 x spring constant x extension2
Turning Moment = Force x distance from pivot
Mechanical advantage = Load / Effort
Pressure = Force/Area
Change in Pressure = Change in depth x density of liquid x gfs

3. Speed, distance and time.
A dog runs 75 metres in 15 seconds.
1: What would we use to measure the time and the distance accurately?
2: Which equation would you use to work out the speed?
3: What is the speed of the dog?
We have worked out that the speed of the dog is 5 m/s
If the speed of the dog increased to 10 m/s, how long would it now take to run the 75 metres?

4. Speed and distance / time graphs
Distance (meters) A 40 30 B 20 C 10
Time (secs)
What does the steepness (gradient) of a distance / time graph tell us?
What is the speed of C?
Which is going fastest, A,B, or C?

5. Draw a distance / time graph for: A: an object that is speeding up
Higher
Draw a distance / time graph for:
A: an object that is speeding up
B: an object that is slowing down
m/s2
Acceleration is measured in …………………………..
Higher: - Acceleration is a change in what?

6. Acceleration and speed / time graphs
Speed (m/s) A 10 8 6 B 4 C 2
Time (secs)
What does the steepness (gradient) of a speed / time graph tell us?
What is the acceleration of A?
How far has C moved in the first 10 seconds?

7. Draw a speed / time graph for:
Higher
Draw a speed / time graph for:
A: an object that has increasing acceleration
B: an object that has decreasing acceleration
THIS DOES NOT MEAN SPEEDING UP AND SLOWING DOWN!

8. Speed combined with direction
Velocity is …………………………..
Positive, eg 6 m/s
Negative, eg - 6 m/s
What is the relative velocity in the above?

9. The relative velocity is ……… m/s
Relative Velocities
6 m/s
2 m/s
The relative velocity is ……… m/s

10. 15/11/2018
Vector quantities have a magnitude and units, but also have a specific direction.

11. Forces as vectors Lots of forces! Reaction (Normal) 10000N 300N 1000N
Air
Resistance
Thrust
Weight
10000N
Lots of forces!
Free body force diagram

12. If a car’s speed changes from 5 m/s to 15 m/s in 2 seconds,
what is the car’s acceleration?
Change in speed = 10 m/s and it took 2 seconds, so
acceleration = 10/2 = 5 m/s2

13. Force = mass x acceleration,
so the force on the person will be less if acceleration is a smaller number
Or we could say
Force = change in momentum / time
so the force on the person will be less if the time to stop is longer

14. Force
What force is required to accelerate a
cannonball at 3 m/s/s if the mass of the
ball is 8 Kgs?
Force = mass x acceleration
So force = 8 x 3 = 24 Newtons

15. How are mass and weight related?
What is mass measured in?
What is weight measured in?
Which one would be different on the moon?

16. Kinetic energy = ½ m v2 Kinetic Energy What is kinetic energy?
What 2 things does the amount of kinetic energy depend on?
Kinetic energy = ½ m v2
IF YOU ARE DOING HIGHER, REMEMBER:
Doubling the speed will quadruple the amount of kinetic energy
so the braking distance will also quadruple.
What will tripling the speed do?

17. Gravitational Potential Energy
What type of energy do objects have if they are high up?
What does the amount of GPE depend on?
GPE = m g h where g is the gravitational field strength
What happens to the GPE of an object when it falls?
If an object has reached terminal velocity, what happens to the
GPE lost when it falls further?

19. Newton’s Third Law
Every action has an equal and opposite reaction

20. Falling objects Why do things accelerate as they fall?
What force acts upwards as an object falls?
If these 2 forces are equal, what happens to the speed of the object?
What happens if the air resistance is increased?

22. Higher:
Larger area  more air resistance (drag)  lower terminal velocity
How does the gravitational field strength vary at different places on the Earth

23. More on air resistance
Lots of air resistance so lower top
speed
Less air resistance so higher top
speed

24. Hurts a lot! Not too bad! Momentum
What does the amount of momentum depend on?
Momentum = mass x velocity
Also, force = change in momentum / time
This equation is important in car safety because it means
that if the time taken to stop is longer, then the force on
the body will be less.
Hurts a lot!
Not too bad!

25. Conservation of momentum
Momentum is always conserved in any event or interaction:
initial momentum
final momentum =
When a snooker ball collides with another, what happens to the momentum of each ball?
Momentum is not created or lost, but transferred from one object to the other.

26. If a gun fires a bullet at 300 m/s, what is the recoil velocity of the gun?
Mass of gun + man = 100 kgs and mass of bullet = 20 grams.
Momentum before gun is fired = 0
After gun is fired:
momentum to the right = 0.02 x 300 = + 6 kg m/s
momentum to the left = x V, where V is the recoil velocity of the gun.
Therefore 6 – 100V = 0
V = 0.06 m/s
6 = 100V

27. Work Done and Power
Which equation do we use to work out the amount of work done?
What work is done when a man pushes a
donkey 10 metres along a road using a force of 50 Newtons?
Work done = Force x distance
So work done = 10 x 50 = 500 Joules
Why is no work being done by the man?
If it took the man 100 seconds to push the donkey,
what is the power in the man’s arms?
Power = work done / time
So power = 500 / 100 = 5 Watts

28. Work Done and Power The man does 600 joules of work when
higher
Work Done and Power
The man does 600 joules of work when
he pushes the donkey 10 metres. What
force does he use?
Work done = Force x distance
So 600 = F x 10
F = 60 Newtons
If the power in the man’s arms is 30 Watts, how long
would it take to push the donkey?
Power = work done / time
So 30 = 600 / t
So t = 20 seconds

29. If we look at the power of different cars, what difference is
it likely to make if a car is more powerful?
….Uses more fuel and produce more pollution
Higher:
Work done = force x distance
Power = work done / time
So power = force x distance / time
Since distance / time = speed, we can say
Power =force x speed
You need to understand the derivation of this equation and be able to use it.

30. SPRING CONSTANT Energy = 0.5 x spring constant x extension2 E= 0.5kx2
Force = spring constant x extension
(N) (N/m) (m)
F = kx
Energy = 0.5 x spring constant x extension2
E= 0.5kx2
15/11/2018

34. Plenary force transferred here force applied here
Pressure inside all parts of the
hydraulic system is the same.
Calculate the pressure exerted on the liquid if a force of 5N is applied to a small area of 1cm2.
Calculate the force the pressure of the liquid exerts on a larger area of 10cm2.
P = 5N ÷ 1cm2 = 5 N/cm2
F = 5 N/cm2 x 10cm2 = 50N