M-EngMom19: Conservation of angular momentum: The rattleback
 
PIRA: 1M40.90 

Equipment: rattleback found in Set 10, Cabinet 3. The rattleback is also called a Celt or a wobblestone.

Procedure: "Angular momentum conservation appears to be violated by an oddly shaped stick that reverses its direction of spin only when spun in one direction, an effect that is due to coupled oscillations.

"Giving the rattleback a rocking motion will cause it to begin to rotate in one direction, because of the peculiar shape of its bottom. Conversely, a rotation in this direction contributes to a rocking motion, but in a cumulative manner only when the periods of rocking and rotation match. This two-way coupling between rocking and rotation is the reason the rattleback begins to rock once its spin rate slows sufficiently, and the reason the rocking in turn gives rise to a small spin in the opposite direction. No such peculiar behavior occurs if the rattleback is spun in the opposite direction, since the asymmetrical shape of its bottom causes the rocking motion to be coupled to a rotation in only one direction."-from "Turning the World Inside Out" by Robert Ehrlich

References:

(1) Jearl Walker, "The amateur scientist," Scientific American 241: 172-184 (1979).

(2) Thomas R. Kane and David A. Levinson, "Realistic mathematical modeling of the rattleback," International Journal of Non Linear Mechanics 17: 175 (1982).