Motion Notes 3

Forces : Terminal velocity

Terminal VelocityTerminal VelocityConsider 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

zero

accelerates

increase

balance

constant

How the forces change with time.

KEYWeight

(constant value and always present)

Air resistance (proportional to the

speed)

Resultant force(the bigger the

unbalanced force the greater the

acceleration)

Terminal VelocityTerminal 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 _______ until it balances his _________. The skydiver has now reached a new, lower ________ _______.

increasesslowing down

decreaseweight

terminal velocity

Velocity-time graph for the sky Velocity-time graph for the sky diverdiver

Velocity

Time

Speed increases…

Terminal velocity reached…

Parachute opens – diver slows down

New, lower terminal velocity reached

Diver hits the ground

On the Moon

Stopping = thinking + Stopping = thinking + braking braking distance distance distancedistance 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

Answers!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 :

Too much alcohol

Thinking distance

Tiredness

Too many drugs

More answers!More answers!

Braking

distance

Wet roads

The speed of the car

Tyres/brakes worn out

Icy roads

• The braking distance is the distance the car moves while the brakes are being depressed.

Typical Stopping Distances

20MPH 6 metres   6 metres ………….. 12 metres

30MPH 9 metres     14 metres …………. 23 metres

40MPH 12 metres 24 metres ……..………. 36 metres

50MPH 15 metres 38 metres ………….... 53 metres

60MPH 18 metres 55 metres ……..……… 73 metres