# Conservation of energy of released ball

1. Apr 17, 2006

### O.J.

suppose we have a ball held at a certain height above the ground where it has 0 KE and x potential enegy. as its release it fall down with uniform acceleration so its KE starts increasing while its GPE starts decreasing. Now suppose a ball is acted upon by a force (say air resistance) causin it to fall with constant speed where it has constant KE while its GPE is decreasing. Where is this energy missing going to?> heat due to friction with air? doesnt seem really convincing to me that all the lost GPE is converted to heat.

a question in one of my excercises asked: explain how can a sphere falling through a liquid have a constant KE but decreasing GPE/? i assumed this is relevant so im putting it across too.

2. Apr 17, 2006

### Hootenanny

Staff Emeritus
Why isn't it convincing that the energy 'lost' is converted to heat?

As for you exercise question, have you heard of the term 'terminal velocity'?

Regards,
~Hoot

3. Apr 17, 2006

### O.J.

i've heard of it. but question is, how come the sphere loses GPE but maintains a consant KE? is it because it's doin work against viscous drag?

4. Apr 17, 2006

### Hootenanny

Staff Emeritus
You've got it in one. At terminal velocity the gravitational force is equal the the drag force created by the fluid throught which it is travelling. The air resistance does negative work on the ball becuase it is acting in the opposite direction to the velocity.

Regards,
~Hoot