The Rattleback is a long and thin half elliptical shape formed in plastic so that it has a slightly offset center of gravity. This offset gravity causes the Rattleback to spin in directional rotation of choice, usually counterclockwise. If you attempt to spin the Rattleback in the clockwise direction, strong preference will cause the Rattleback to "rattle" back and forth after few rotations, stopping and then reversing the rotation back to the preferred clockwise direction. The directional preference is so strong that if the Rattleback is at a stand still and you push down on one end it will begin turning. Color may vary. Comes with a Teacher's Guide and reproducible Student Handout.