1. Terminal velocity and stopping distance
Forces :
Terminal velocity and stopping distance

2. By the end of this presentation, you should be able to:
Describe and explain what is meant by terminal velocity.
Describe and explain how forces change on a falling object.
Recall and explain the meanings of the terms ‘stopping distance’, ‘thinking distance’ and ‘braking distance’ and the factors which affect them.

3. W Richards Worthing High School
Terminal Velocity
Consider a skydiver:
At the start of his jump the air resistance is _______ so he
____ downwards.
zero
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
balance
constant

4. How the forces change with time.
KEY
Weight
(constant value and always present)
Air resistance (proportional to the speed)
Resultant force
(the bigger the unbalanced force the greater the acceleration)

5. Terminal Velocity 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 _______ until it balances his _________. The skydiver has now reached a new, lower ________ _______.
decrease
weight
terminal velocity

6. Velocity-time graph for the sky diver
Parachute opens – diver slows down
Velocity
Speed increases…
Terminal velocity reached…
On the Moon
Diver hits the ground
New, lower terminal velocity reached
Time

7. Stopping = thinking + braking distance distance distance
What is stopping distance?
What is thinking distance? What factors will affect it?
What is braking distance? What factors will affect it ?
How can we work out how fast an object is travelling?
Speed = total distance / time taken

8. Answers!
The stopping distance is the distance the car travels from the time the driver realises that he needs to stop, to the time when the car actually stops moving.
The thinking distance is the distance the car moves between the driver realising that he has to stop and when he steps on the brake.
Factors that will affect thinking distance :
Tiredness
Too much alcohol
Thinking distance
Too many drugs

9. More answers!
The braking distance is the distance the car moves while the brakes are being depressed.
Wet roads
Icy roads
Braking
distance
Tyres/brakes worn out
The speed of the car

10. Typical Stopping Distances
20 MPH 6 metres   6 metres ………….. 12 metres
30 MPH 9 metres     metres …………. 23 metres
40 MPH metres metres ……..………. 36 metres
50 MPH metres metres ………… metres
60 MPH metres metres ……..……… 73 metres
Typical Stopping Distances