Rattleback
semi-ellipsoidal top which will rotate on its axis in a preferred direction, but which, if spun in the opposite direction, becomes unstable, ‘rattles’ to a stop and reverses its spin to the preferred direction
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.
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 counterintuitive behavior makes the rattleback a physical curiosity that has excited human imagination since prehistoric times.
A rattleback may also be known as a "anagyre", "(rebellious) celt", "Celtic stone", "druid stone", "rattlerock", "Robinson Reverser", "spin bar", "wobble stone" (or "wobblestone") and by product names including "ARK", "Bizzaro Swirl", "Space Pet" and "Space Toy".
History
Archeologists who investigated ancient Celtic and Egyptian sites in the 19th century found celts which exhibited the spin-reversal motion. The antiquarian word celt (the "c" is soft, pronounced as "s") describes lithic tools and weapons shaped like an adze, axe, chisel, or hoe.
The first modern descriptions of these celts were published in the 1890s when Gilbert Walker wrote his "On a curious dynamical property of celts" for the Proceedings of the Cambridge Philosophical Society in Cambridge, England, and "On a dynamical top" for the Quarterly Journal of Pure and Applied Mathematics in Somerville, Massachusetts, US.
Additional examinations of rattlebacks were published in 1909 and 1918, and by the 1950s and 1970s, several more examinations were made. But, the popular fascination with the objects has increased notably since the 1980s when no fewer than 28 examinations were published.
“Rattleback” enters the record as semi-ellipsoidal top which will rotate on its axis in a preferred direction, but which, if spun in the opposite direction, becomes unstable, ‘rattles’ to a stop and reverses its spin to the preferred direction. Crown Archives preserves that source wording while asking what Rattleback, semi-ellipsoidal and will can confirm, complicate or overturn.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 12, 2026. The linked authority identifier is Q1738399. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1909 and 1918.
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This entry incorporates text from “Rattleback” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.