Why do hard things still bounce when dropped?


A ball bounces because it changes shape on impact and the momentum from changing the shape back to normal makes it go up again. Then why rock solid stuff also bounce when dropped? Ive seen pebbles bounce when dropped. My phone bounces like 1 or 2 times when i drop it. Why?

In: 2

Same reason. Either they (and/or the ground beneath them) flex and rebound in the exact same way. It just happens a lot quicker and it’s so subtle that you can’t see it.

Look up slow motion footage of a golf ball being teed off, for example. I would normally consider a golf ball to be a rigid object, but in the instant of impact, it will deform just like a rubber bouncy ball does.

You’ve got it kind of backwards. If everything were perfectly rigid and never deformed, then everything would bounce back to the spot it was dropped from. That is called an “elastic collision”. A bouncy ball is able to get close to a truly elastic collision by not permanently deforming, like you said.

But relatively rigid things can bounce even better than the bouncy ball, like a steel ball bearing, it bounces incredibly well on a steel plate, because there’s no where else for the energy to go.

What causes stuff to *not* bounce is that the energy goes somewhere else. Either it cracks the screen in your phone’s case, deforms the ground in the case of a padded floor, or a bunch of other things.

But the default state of something hitting the ground is for it to bounce back. The energy has to specifically go somewhere else in order for it not to bounce.

I object that would not deform at all would be a perfect [https://en.wikipedia.org/wiki/Elastic_collision](https://en.wikipedia.org/wiki/Elastic_collision) where all kinetic energy and momentum are preserved. In vaccume bouncing like that would continue forever. Individual atoms will bounce like that but objects on the human scale will flex to some degree.

Steel ball bounces very well if you bounce them on somting equally hard, it most situation the will be the harder object and the ground before so there is not a lot of bouncing but look at what happens whe [Ball bearing bounces on a anvil](https://www.youtube.com/watch?v=KuX5s5r9i74)

Here you have metal and other hard balls like glass boing for a long time on a special metal object https://www.youtube.com/watch?v=QpuCtzdvix4

First, not everything goes back to the original shape. It can deform permanently. This is why snowballs and play-doh (plasticine) do not bounce.

For things that do spring back to the original shape, it still takes energy to deform it, and it does not spring back with the same force. Memory foam is a good example of something that absorbs most of the energy – it does go back to the original shape but does not give back most of the energy it receives. Generally, the harder the object, the less energy it absorbs.

There is no such thing as a true solid, look at slow motion videos of a “solid” object getting hit.