or, how cats survive falls from tall buildings Falling Objects or, how cats survive falls from tall buildings

Lesson objectives Know: what ‘terminal velocity’ means Understand: why falling things reach a terminal velocity Be able to: describe and explain the stages in a parachute jump (including the forces involved and whether or not acceleration is happening at each stage)

Terminal velocity extra questions Explain why a falling human reaches a higher terminal velocity than a falling cat. Explain why a falling human without a parachute reaches a higher terminal velocity than a falling human with one. Parachutes on the moon? – Comment on their usefulness. Film of parachute jumpers often makes it look as though they shoot upwards when their parachute opens. They don’t – so why does it look that way? Sketch a graph showing the speed of a skydiver from the moment she jumps to the moment she lands. What possible reasons can you think of for why the exam board decided terminal velocity was important enough to be part of the Physics 2 module?

Terminal velocity extra questions – outline answers The object accelerates until the air resistance matches the weight. A human has a bigger weight, so has to reach a higher speed before the air resistance matches it. A falling human with a parachute has a greater air resistance at a given speed, so does not have to reach as high a speed for air resistance to match weight. Parachutes are useless on the moon, as there is no air, so no air resistance. Everything keeps on accelerating to the end of its fall. The camera operator remains in free fall while he films the parachutist opening his parachute. At this point, the parachutist suddenly slows down relative to the camera operator, who shoots past him. This makes the parachutist appear to move upwards.

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