UIUC Physics
Lecture Demonstration




Demo # 1148

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Rattleback (Spin Toy)

ID # 1148


A half-ellipsoid object carved in such a way that is will only spin in one direction. A Rattleback is an ellipsoid cut in half so that the long axis of the rounded bottom is skewed from the axis of the flat top. This skewing, the shape of the bottom and the distribution of its mass are all responsible for the Rattleback’s stubborn tendencies. When spun in an unstable direction friction causes it to slow and begin to oscillate, or rock up and down; it can also be induced to spin by pressing down on one end. The remaining "spin energy" is converted to "oscillatory energy" and then back to "spin energy" in the opposite direction. Each Rattleback’s particular shape determines whether it will favor a clockwise or counterclockwise rotation.

Picture of Rattleback (Spin Toy)

Physics Concept:

  • Mechanics
  • Rotational Dynamics
  • Rotational Stability

The demonstration takes about 1 minute to perform.

© Dept. of Physics, Univ. of Illinois at Urbana-Champaign, 1996.