The Rattleback is a long, thin, half-elliptical shape formed in plastic. It has a slightly offset center of gravity, which causes the Rattleback to spin in a directional rotation of choice, usually counterclockwise. If you attempt to spin the Rattleback in the clockwise direction, a strong preference will cause the Rattleback to “rattle” back and forth after a few rotations, stopping and then reversing the rotation back to the preferred counterclockwise direction. The directional preference is so strong that if the Rattleback is at a standstill and you push down on 1 end, it will begin turning.
See the Teacher's Guide and Student Handout to learn how to use this to learn about center of mass, angular momentum, and more!
About 4" long.