1M40.90 Celt (Rattleback)


Spin reversal, change in direction of rotational energy


When rotated in one direction, the celt will stop and rotate in the opposite direction.



  • [1] Celt (also known as a rattleback)


  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.


Additional Resources


  • PIRA 1M40.90
  • 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


  • Don't attempt this at home!

Last revised

  • 2018


  • Original construction: purchased.

Related AV

Related demos


If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.