Rattleback - Breaking the Laws of Physics? (Walter Lewin rotation experiment) Lately i have been watching the MIT Physics Lectures from Dr. Walter Lewin. I find his passion while teaching very fascinating and inspiring. Any way, in the end of the lecture about Torque he showed a weird phenomenon which ,he admitted, baffled himself for a while. 
He place a piece of plastic onto the projector's glass surface and he spined it counter clockwise and the result was as expected. The body spined till the friction (however small) stopped it. However when he spinned it clockwise the friction brought it to a halt and then its direction of rotation is reversed.
For your convenience if you haven't seen the lecture. Click here (and go to 46th minute)
I asked my physics teacher and he assumed that there is either some kind of liquid in the plastic and the body when spinned changes it's moment of inertia and that's how the motion is affected or there is some monkey business. However that doesn't seem likely to me.
So my question is how is this motion possible?
And could you share with me the mathematical approach of the motion?
 A: This quite special top is called a rattleback, or celt. See Wikipedia : http://en.wikipedia.org/wiki/Rattleback
I quote : "The spin-reversal motion follows from the growth of instabilities on the other rotation axes, that are rolling (on the main axis) and pitching (on the crosswise axis). (...) The amplified mode will differ depending on the spin direction, which explains the rattleback's asymmetrical behavior. Depending on whether it is rather a pitching or rolling instability that dominates, the growth rate will be very high or quite low."
You can find some for sale or even build your own : http://www.iop.org/EJ/abstract/0143-0807/11/1/112
A: I suspect this is possible in the same way as when you strike a billiard ball below its center of mass: the  ball moves forward, stops, and moves back because when it stops, it still has rotation energy and tries to keep rotating, but friction opposes this rotation and causes the ball's motion back. So the plastic piece probably still has some rotation energy when it stops. Why the results depend on the sense of rotation? Probably, because of some "chiral" mass distribution. 
