# Query on physics of a tennis ball

1. Dec 16, 2008

### Confuzzled

In my As physics class today the topic of this arrived, which has been annoying me ever since, i am hoping you may be able to help, as hours of searching the internet i have failed. :(

I understand that when a ball is held at a certain height that it has stored energy, GPE. And when this ball is dropped this energy turns into Kinetic Energy, my query is on what is the energy, at the point it hits the ground? I would assume elastic energy, but am unclear.

Also if this said ball was to be heated, I it would bounce a higher distance due to temperature being proportional to pressure? And pressure being the answer to how much something would bounce? But why is this? What does pressure do to the insides of that tennis ball?

Thanks Confuzzled

2. Feb 10, 2009

### greg136

As the ball is falling, the gPE 'turns' into Kinetic, Heat and Sound energies (albeit, the last two are slight in comparison).

Similarly, when the ball hits the ground, it 'loses' Kinetic energy to more heat and sound, and indeed as you said ePE.

Conservation of energy means that the ball will not bounce higher than the height you dropped it from, unless you some how superheated it during it's fall.

3. Feb 10, 2009

### Nabeshin

The question about pressure is interesting; think about it in your every day life. A poorly inflated basketball does not bounce nearly as well as a well inflated one, why?

The answer relates to your first question, I think. We can easily analyze the fall of the tennis ball as a straight conversion between gravitational potential energy and kinetic energy. However, when the ball hits the ground KE is zero and PE is zero, so how can it bounce back? The ball behaves (roughly) like a spring in that it is compressed and stores energy, which it releases and bounces back up. However, a tennis ball is by no means a perfect spring so the more the compression, the greater the loss of energy due to heat, sound, and other external factors.

So, when you have a tennis ball with high internal pressure, as it hits the ground it has a much higher "spring constant", i.e it will compress far less and thus suffers less loss due to external factors and will bounce back with a height closer to that of the original.

Hope this makes sense!
Cheers