Rattleback: Difference between revisions

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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 [[Angularangular momentum#Conservation of angular momentum|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.<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 |dead-url=yes |archive-date=2004-03-06 |publisher=[[University of Cambridge]] |accessdate=2013-10-19 }}</ref>

This makes the rattleback a physical curiosity that has excited human imagination since prehistorical times.<ref>"celt, n.2". OED Online. September 2012. Oxford University Press. 1 October 2012 <http://www.oed.com/view/Entry/29533?isAdvanced=false&result=2&rskey=EPfrjA&></ref>

A rattleback may also be known as a "anagyre", "[[Celtcelt (tool)|celt]]", "Celtic stone", "rebellious celt", "rattlerock", "spin bar", "Robinson Reverser", "wobble stone" (or "wobblestone") and by the product names "ARK", "Bizzaro Swirl", "RATTLEBACK", "Space Pet" and "Space Toy".

==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]] [[Archaeologyarchaeology|sites]] in the 19th century found celts which exhibited the spin-reversal motion. The [[antiquarian]] word "[[Celtcelt (tool)|celt]]" (the "c" is pronounced as "s") describes [[adze]]-, [[axe]]-, [[chisel]]- and [[Hoehoe (tool)|hoe]]-shaped [[Lithiclithic analysis|lithic]] tools and weapons.

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, MassMassachusetts, 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.

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==Size and materials==

[[File:Celt with weights of gemstone turtles-01.jpg|thumb|200px|Carved wooden rattleback]]

While rattleback [[Artifactartifact (archaeology)|artifact]]s 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, [<ref>http://www.exo.net/~pauld/TomTits2000/europetrip/technorama%20lecture/technoramalecture.html],</ref> 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 [.<ref>http://boisselier.ca/en/products-page/curiosities/].</ref>

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.

==Physics==

[[Image:Rolling-pitching.png|thumb|200px|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/ | title=Keith Moffatt, Cambridge Univ. & KITP, Rattleback Reversals: A Prototype of Chiral Dynamics}}</ref>

[[File:Spoon_Celt.webm|thumb|Rattleback made with spoon exhibiting multiple spin reversals. Original video and idea by Prof. Christian Ucke.]]