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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 counterintuitive behavior makes the rattleback a physical curiosity that has excited human imagination since prehistoric times.<ref>
A rattleback may also be known as a "anagyre", "(rebellious) [[celt (tool)|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".
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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.{{citation 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.<ref>{{cite journal
| date=1896
| last1=Walker | first1=G. T. | authorlink1=Gilbert Walker (physicist)
| title=On a dynamical top
| journal=[[The Quarterly Journal of Pure and Applied Mathematics|Quarterly Journal of Pure and Applied Mathematics]]
| volume=28
| pages=175–184
| url={{GBurl|1_zxAAAAMAAJ|p=175}} }}</ref><ref>{{cite journal
| date=1895
| last1=Walker | first1=G. T. | authorlink1=Gilbert Walker (physicist)
| title=On a curious dynamical property of celts
| journal=[[Mathematical Proceedings of the Cambridge Philosophical Society]]
| volume=8
| issue=5
| pages=305–306
| url=https://archive.org/details/proceedingsofcam8189295camb/page/304/mode/2up}}</ref>
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.
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==Physics==
[[Image:Rolling-pitching.png|thumb|Rolling and pitching motions|left]]
The spin-reversal motion follows from the growth of [[flight dynamics|instabilities]] on the other rotation axes, that are rolling (on the main axis) and pitching (on the crosswise axis).<ref>{{Cite web | url=http://online.kitp.ucsb.edu/online/dynamo08/moffatt/ |date=2008
[[File:Spoon_Celt.webm|thumb|Rattleback made with spoon exhibiting multiple spin reversals.]]
When there is an asymmetry in the mass distribution with respect to the plane formed by the pitching and the vertical axes, a coupling of these two instabilities arises; one can imagine how the asymmetry in mass will deviate the rattleback when pitching, which will create some rolling.
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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.
For a comprehensive analysis of rattleback's motion, see V.Ph. Zhuravlev and D.M. Klimov (2008).<ref>{{cite journal |first1=V.Ph. |last1=Zhuravlev
Realistic mathematical modelling of a rattleback is presented by G. Kudra and J. Awrejcewicz (2015).<ref>{{Cite journal|title=Application and experimental validation of new computational models of friction forces and rolling resistance|first1=Grzegorz|last1=Kudra|first2=Jan|last2=Awrejcewicz|date=September 1, 2015|journal=Acta Mechanica|volume=226|issue=9|pages=2831–2848|doi=10.1007/s00707-015-1353-z|s2cid=122992413|doi-access=free}}</ref> They focused on modelling of the contact forces and tested different versions of models of friction and rolling resistance, obtaining good agreement with the experimental results.
Numerical simulations predict that a rattleback situated on a harmonically oscillating base can exhibit rich bifurcation dynamics, including different types of periodic, quasi-periodic and chaotic motions.<ref>{{cite journal |first1=J. |last1=Awrejcewicz
==See also==
*[[Spinning top]]
*[[Tesla's Egg of Columbus]]
*[[Tennis racket theorem]]
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==References==
{{reflist|25em}}
{{refbegin}}
*{{cite journal |first=Hermann |last=Bondi |title=The rigid body dynamics of unidirectional spin |journal=Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences |volume=405 |issue=1829 |pages=265–274 |date=1986 |doi=10.1098/rspa.1986.0052 |jstor=2397977 |bibcode=1986RSPSA.405..265B }}
*{{cite journal |first=A.B. |last=Pippard |title=How to make a celt or rattleback |journal=European Journal of Physics |volume=11 |issue=1 |pages=63–64 |date=1990 |doi=10.1088/0143-0807/11/1/112 }}
{{refend}}
==External links==
{{Commons category|Celtic rattlebacks}}
*Doherty, Paul. Scientific Explorations. [http://www.exo.net/~pauld/activities/sweden/spoonrattleback.html ''Spoon Rattleback''.] 2000.
*{{cite web |title=Celt Spoon |date=2002 |publisher=[[Flinn Scientific Inc.]]
*Sanderson, Jonathan. Activity of the Week: [https://web.archive.org/web/20061021205047/http://www.scienceyear.com/about_sy/news/ps_176-200/ps_issue182.html#4 Rattleback].
*Simon Fraser University: [https://web.archive.org/web/20120205181113/http://www.sfu.ca/physics/ugrad/courses/teaching_resources/demoindex/mechanics/mech1q/celt.html ''Celt''.] physics demonstration. Burnaby, British Columbia, Canada.
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