in the other direction, it soon starts wobbling or rattling about its short axis and stops spinning, then it starts to rotate in the opposite direction. One who has studied classical mechanics must be amazed by this reversal in spinning, because it apparently seems to violate the angular momentum conservation, and the chirality emerges from a seemingly symmetrical object.

There are three requirements for a rattleback to show this reversal of rotation: (1) the two principal curvatures of the lower surface should be different, (2) the two horizontal principal moments of inertia should also be different, and (3) the principal axes of inertia should be misaligned to the principal directions of curvature. These characteristics induce the coupling between the spinning motion and the two oscillations: the pitching about the short horizontal axis and the rolling about the long horizontal axis. The coupling is asymmetric, i.e., the oscillations cause torque around the spin axis and the signs of the torque are opposite to each other. This also means that either the pitching or the rolling is excited depending on the direction of the spinning. We will see that the spinning couples with the pitching much stronger than that with the rolling; 