Celt, or Rattleback

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Equipment: A Celt or Rattleback.

What it does: When rotated in one direction, the celt will stop and rotate in the opposite direction.

Concepts Demonstrated: Spin reversal; change in direction of rotational energy.

Classroom assembly:

  1. Place the celt on the glass surface of the overhead projector (mylar will interfere with the rotation of the celt).
  2. Flick the celt with your finger to cause it to rotate like a top. In one direction, the celt will rotate normally. In the other direction, the celt will eventually stop rotating and begin to rotate in the opposite direction. Note that as the rotation slows, the celt will oscillate around its long axis.
  3. Push down on one end of the celt to cause it to oscillate like a see-saw. The celt will begin to rotate like a top.

Cautions: None.

Setup Time: Short.

Difficulty: Straightforward.

Visibility: High. This demonstration can be shown on the overhead projector and is appropriate for large lecture halls.

Related demonstrations:

References: PIRA 1Q60.XX

* Indicates copy on file

Original Construction: Purchased.

Disclaimer: All demonstrations are posted for the convenience and benefit of faculty and staff in the Department of Physics at Simon Fraser University and are not intended for outside use. The author(s) assume no responsibility or liability for the use of information contained on this site. Warnings and precautionary measures listed on this site assume normal operation of equipment and are not inclusive. Demonstrations may pose a significant hazard and can, in some instances, result in death; reasonable safety precautions must be taken. Demonstrations should be performed by qualified individuals only.

Prepared by Jeff Rudd, 1999
Revised by Laura Schmidt, 2007

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