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

• *Crane, H. Richard, "How Things Work: The Rattleback Revisited" TPT 29(5), 278-279, (May 1991).
• *Edge, Ronald D. and Richard Childers, "String and Sticky Tape: Curious Celts and Riotous Rattlebacks" TPT 37(2), 80, (Feb 1999)
• *Walker, Jearl , "Rattlebacks and Tippe Tops" in "Roundabout: The Physics Of Rotation in the Everyday World", 33-38 (from the Amateur Scientist, Scientific American Oct 1979, 172)
• *Pippard, AB, "How to make a celt or rattleback", Eur J Phys 11, 63-4, (1990)
• *Bondi, Sir Hermann, "The rigid body dynamics of unidirectional spin", Proc R Soc Lond A 405, 265-74, (1986)
• Walgate, Robert, Tops That Like to Spin One Way, Nature Vol 323, 204, (18 Sept. 1986) - a notice of Bondi's article
• H. Crabtree, An Elementary Treatment of the Spinning Tops and Gyroscopic Motion, Chelsea, NY., (1967) - not seen, Walker refers to this but it isn't at SFU
• Allan J. Boardman, The Mysterious Celt; Fine Woodworking No. 53, 68-69, (July/Aug 1985) - not seen

Original Construction: Purchased.