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Can spin result in an increase of velocity?

by d1v1n1ty nb
Tags: increase, result, spin, velocity
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d1v1n1ty nb
Oct17-06, 10:10 AM
P: 5
If a spinning ball hits the floor is it possible for it to increase in velocity in the direction it is travelling? If so could you please explain with an example? And what Equations would you use? Thanx.
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Oct17-06, 11:57 AM
P: 22,239
Absolutely - you can do all sorts of crazy things with a rubber ball. If you bounce it from the ground to a wall at a low angle (throw it near the corner), you can even get it to bounce back and forth as its direction of spin and direction of motion both reverse every time it hits the ground.

It may be difficult to caluclate (or rather, difficult to get proper data/assumptions), but you could use angular momentum converted to linear momentum.
Meir Achuz
Oct17-06, 02:13 PM
Sci Advisor
HW Helper
PF Gold
P: 1,991
Draw a FBD of the ball in contact with the surface, including friction.
Then just apply f=ma and T=I alpha.
It is called a slam in ping pong.

Oct17-06, 03:38 PM
P: 22,239
Can spin result in an increase of velocity?

That would be difficult because the force varies and you don't know things like time of contact. It is very dependent on many specific properties of the objects. I was thinking that given a certain elastic modulous, a specific fraction of the angular momentum would be converted to linear momentum.
Oct17-06, 06:31 PM
Sci Advisor
PF Gold
P: 39,345
But you can argue "conservation of energy". If the impact reduces the spin, then the energy due to rotation is reduced and can go into linear kinetic energy.

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