Rattleback: Difference between revisions

Revision as of 08:08, 16 April 2024

Revision as of 20:46, 16 April 2024

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{{Short description|Semi-ellipsoidal spinning top}}

[[File:Rattleback in action.ogv|thumb|A rattleback in action]]

A '''rattleback''' is a semi-ellipsoidal [[Spinning top|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 [[angular momentum#Conservation of angular momentum|conservation of angular momentum]].{{citation needed|date=April 2024}} 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.<ref name="motivate">{{cite web|title=Introduction to Hugh's Talk |work=Millennium Mathematics Project |url=http://motivate.maths.org/conferences/conf14/c14_talk1.shtml |archive-url=https://web.archive.org/web/20040306062339/http://www.motivate.maths.org/conferences/conf14/c14_talk1.shtml |url-status=dead |archive-date=2004-03-06 |publisher=[[University of Cambridge]] |access-date=2013-10-19 }}</ref>

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==History==

[[File:RATTLEBACK - ANAGYRE -(GAEL 24 inches) - Emmanuel Peluchon.jpg|thumb|Large rattleback made from different wood densities]]

Archeologists who investigated ancient [[Celt]]ic and [[Ancient Egypt|Egyptian]] [[archaeology|sites]] in the 19th century found [[celt (tool)|celts]] which exhibited the spin-reversal motion.{{cncitation needed|date=November 2022}} The [[antiquarian]] word ''celt'' (the "c" is soft, pronounced as "s") describes [[lithic analysis|lithic]] tools and weapons shaped like an [[adze]], [[axe]], [[chisel]], or [[hoe (tool)|hoe]].

The first modern descriptions of these celts were published in the 1890s when [[Gilbert Walker (physicist)|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.

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The amplified mode will differ depending on the spin direction, which explains the rattleback's asymmetrical behavior. Depending on whether it is rather a pitching or rolling instability that dominates, the growth rate will be very high or quite low.

This explains why, due to friction, most rattlebacks appear to exhibit spin-reversal motion only when spun in the pitching-unstable direction, also known as the strong reversal direction. When the rattleback is spun in the "stable direction", also known as the weak reversal direction, friction and damping often slow the rattleback to a stop before the rolling instability has time to fully build. Some rattlebacks, however, exhibit "unstable behavior" when spun in either direction, and incur several successive spin reversals per spin.<ref>{{cite journal|title=Spin Reversal of the Rattleback: Theory and Experiment|first1=A.|last1=Garcia|first2=M.|last2=Hubbard|date=8 July 1988|journal=Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=418|issue=1854|pages=165–197|doi=10.1098/rspa.1988.0078|bibcode = 1988RSPSA.418..165G|s2cid=122747632}}</ref>

Other ways to add motion to a rattleback include tapping by pressing down momentarily on either of its ends, and rocking by pressing down repeatedly on either of its ends.