Q:

when dropping two objects, with the same size but different weights, from the same height onto a trampoline wich object will bounce back higher? the lighter or heavier object?

- owen empey (age 12)

annapolis,md

- owen empey (age 12)

annapolis,md

A:

If the world were very simple, all the different weights would bounce back to the same height as they started. That’s because at that height all their initial gravitational potential energy is back, and there's no energy left to go any higher.

You know that in the real world the weights won't bounce up as high as they started, so the question is just which one gets closer. The initial energy dribbles away in two main ways, air friction and internal vibrations in the trampoline. If the objects are the same size and shape, their air friction losses are about the same. That lost energy is a bigger fraction of the lighter object's energy, so it wouldn't bounce as high. The way that energy gets lost into the trampoline itself depends in some complicated way on how much it's stretched. The heavy object stretches it more, and I suspect will lose a bigger fraction of its energy in the bounce. So it's hard to say which will bounce higher. If I had to guess, I'd guess that you'll find the highest bounces for some intermediate weight, big enough for air friction not to be too important but small enough so that the trampoline doesn't stretch a huge amount.

You know that in the real world the weights won't bounce up as high as they started, so the question is just which one gets closer. The initial energy dribbles away in two main ways, air friction and internal vibrations in the trampoline. If the objects are the same size and shape, their air friction losses are about the same. That lost energy is a bigger fraction of the lighter object's energy, so it wouldn't bounce as high. The way that energy gets lost into the trampoline itself depends in some complicated way on how much it's stretched. The heavy object stretches it more, and I suspect will lose a bigger fraction of its energy in the bounce. So it's hard to say which will bounce higher. If I had to guess, I'd guess that you'll find the highest bounces for some intermediate weight, big enough for air friction not to be too important but small enough so that the trampoline doesn't stretch a huge amount.

*(published on 10/22/2007)*