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Forces : Terminal velocity and stopping distance

Forces : Terminal velocity and stopping distance. 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.

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Forces : Terminal velocity and stopping distance

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  1. 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. Terminal Velocity W RichardsWorthing High School 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. KEY Weight (constant value and always present) Air resistance (proportional to the speed) Resultant force (the bigger the unbalanced force the greater the acceleration) How the forces change with time.

  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 Speed increases… Terminal velocity reached… On the Moon New, lower terminal velocity reached Diver hits the ground Velocity 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! Thinking distance • 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 Too many drugs

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

  10. 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 Typical Stopping Distances

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