A spinning cap that reverses direction?

[kyin01]

I was watching a video on where this guy spins a a dial or capsule or a cap (I couldn't really tell, but it was like a long thing cylinder capsule look a like) and well he gave it a quick push and the cap came to a stop and than reverses direction.

What could cause this?


I know that angular momentum is not conserved because of external torque (gravity) and friction causes the thing to come to a halt, but why would it reverse direction. Where does it get the force to reverse direction?

 

[Doc Al]

Rattleback

That's a cool toy called a rattleback. The physics details are non-trivial.

http://en.wikipedia.org/wiki/Rattleback

http://www.4physics.com:8080/phy_demo/rattleback.htm"