page_title: Rattleback
section_title: Size and materials
hierarchical_section_title: Rattleback / Size and materials
caption_attribution_description: Celt are asymmetrical tops which have a preferred direction of spin. If spun in the opposite direction they become unstable and reverse their spin to the preferred direction.
context_page_description: A rattleback is a semi-ellipsoidal top which will rotate on its axis in a preferred direction. If spun in the opposite direction, it becomes unstable, "rattles" to a stop and reverses its spin to the preferred direction.
  This spin-reversal appears to violate the law of the conservation of angular momentum. Moreover, for most rattlebacks the motion will happen when the rattleback is spun in one direction, but not when spun in the other. Some exceptional rattlebacks will reverse when spun in either direction.
  This makes the rattleback a physical curiosity that has excited human imagination since prehistorical times.
context_section_description: While rattleback artifacts are described as stone with various measurements, most which are sold currently as novelty puzzles and toys are described as plastic with measurements of 3.75 inches long x 0.75 inches wide x 0.4375 inches high. Carved wooden rattlebacks are described with a measurement of 5.5 to 6 inches in length. One plastic rattleback made and sold by Charles W. Sherburne is described as 12 inches in length. Glass rattlebacks, and those made of spoons,  are described as being tested with unreported measurements. Larger rattlebacks (up to 8 feet long and 16 inches wide) are made on request by Emmanuel Peluchon for science museums.
  Two rattleback design types exist. They have either an asymmetrical base with a skewed rolling axis, or a symmetrical base with offset weighting at the ends.
caption: Carved wooden rattleback
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