# Velocity dependent forces problem

1. Apr 16, 2004

### retupmoc

I know of velocity dependent forces and the like but have a problem in grasping a problem ive been thinking over for the past few days although i know the answer is really simple. For exampe when a ball hits a wall at speed V, say how do i work out the force. Is it just by using the change of momentum and time of contact?

2. Apr 16, 2004

### arildno

The time-averaged force acting upon the ball can be found in the manner you described.
Notice that this force will be practically infinite, since the contact time is practically zero!

What do you know of collision theory/impact analysis?

3. Apr 17, 2004

### AntiMagicMan

When collisions happen very quickly we tend to talk of an impulse. Defined as a force multiplied by a time, an impulse is equal to the change of momentum (simply N2 rearranged).

If however you know the change of momentum and the time of contact you can work out the force, as force is dp/dt so just divide the two and you have the force.