# Momentum and Friction

1. Jan 13, 2015

### Scheuerf

If a heavy ball is rolling on a surface, it eventually stops due to the frictional force. Where does the momentum of that ball go? Is it lost to heat, or does it maybe cause the earth to move a very small and unnoticeable amount?

2. Jan 13, 2015

### Matterwave

It causes the Earth to move a very small and unnoticeable amount. But you had to have moved the Earth a small and unnoticeable amount when you started the ball rolling so, this should just cancel that out roughly (the center of mass has shifted by a little bit in the process).

3. Jan 13, 2015

### Scheuerf

So is momentum not lost to friction in the same way that kinetic energy is?

4. Jan 13, 2015

### Matterwave

Friction is a force and as such changes the momentum of the ball. But Newton's 3rd law says every force has an equal and opposite reaction force so that momentum is conserved. You could perhaps lose a little bit of momentum to pieces of the ground chipping or to the surrounding air or something, but you would probably just lump those elements together into "Earth".

5. Jan 14, 2015

### CWatters

No. Momentum is always conserved in any type of collision.