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[[Image:Celt_with_gemstone_turtles-01.jpg|thumb|300px|Carved wooden rattleback]]
A '''rattleback''', also known as a "celt," "Celtic stone," "spin bar," "tates," "wobble stone" or "wobblestone," and by the product names "ARK," "RATTLEBACKS" and "Space Pets," is a semi-ellipsoidal [[top]] which will spin on its axis in a preferred direction. But, if spun in the opposite direction, it becomes unstable, "rattles," stops and reverses its spin to the preferred direction.
:''Behold the mysterious celt,''
:''with a property that amuses.''
:''One way it will spin,''
:''the other way it refuses.''
This spin-reversal motion seems, at first sight, to violate the [[angular momentum|angular-momentum]] conservation law of physics. Moreover, for most rattlebacks, the motion will happen when the rattleback is spun in one direction, but not when spun in the other. These two peculiarities make the rattleback a physical curiosity that has excited human imagination since prehistorical times.
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==Size==
While rattleback [[Artifact (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 length x 0.75-inches width x 0.4375-inches height. Carved wooden rattlebacks are described with a measurement of 5.5-inches to 6-inches length. One plastic rattleback made and sold by Charles W. Sherburne is described with a measurement of 12-inches length. Glass rattlebacks, and those made of spoons, are described as being tested with unreported measurements. Larger rattlebacks, and those of other materials, aren't yet reported.
Two rattleback-design types exist. The first enjoys an asymmetrical base where its rolling axis is skewed. The second enjoys a symmetrical base with off-set weighting at the ends of the rattleback.
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*Influenced by the [[Coriolis effect]]
*A "Tates" compass ("He who has a Tates is lost.")
==References==
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Crane [[Doctor of Philosophy|Ph.D.]], H. Richard. "How things work: The rattleback revisited." ''The Physics Teacher'', vol. 29(5), pp. 278-9. American Association of Physics Teachers. College Park, Md. 1991.
Dammermann, W. "Celtic Wackelsteine." Physics in our time, vol. 12, pp. 178-80. 1981.
Edge [[Doctor of Philosophy|Ph.D.]], Ronald D. and Richard Lee Childers [[Doctor of Philosophy|Ph.D.]]. "String and sticky tape: Curious celts and riotous rattlebacks." ''The Physics Teacher'', vol. 37(2), p. 80. American Association of Physics Teachers. College Park, Md. 1999.
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Gray, Andrew. ''Treatise of gyrostatics and rotational motion''. Macmillan Publishers Ltd. London. 1918.
Holzhey, C. and H. Puschmann. "The Celtic Wackelstein: A remarkable gyroscope." Recent Science, vol 1, no. 2, pp. 6-15. 1986.
Magnus, Karl. ''The stability of rotations of a non-symmetrical body on a horizontal surface''. Festschrift Szabo, pp. 19-23, Berlin. 1971.
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[[Jearl Walker|Walker Ph.D., Jearl]]. "Rattlebacks and tippe tops; Roundabout: The physics of rotation in the everyday world." ''Scientific American'', pp. 33-8, 66. Scientific American Inc. New York. 1985.
[[Jearl Walker|Walker Ph.D., Jearl]]. "Puzzling gyroscopes." Spektrum der Wissenschaft, part 1, December 1979, pp. 109-13; part 2, May 1981, pp. 151-7.
[[Gilbert Walker|Walker FRS, Sir Gilbert Thomas]]. "On a curious dynamical property of celts." ''Proceedings of the Cambridge Philosophical Society'', vol. 8, pp. 305-6. Cambridge, England. 1892/5.
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*Brown University: [http://www.physics.brown.edu/physics/demopages/Demo/solids/demos/1q6016.html ''To demonstrate a puzzling mechanical device with unidirectional rotational behavior''.] physics demonstration.
*Flinn Scientific Inc. [http://www.flinnsci.com/Documents/demoPDFs/PhysicalSci/PS10440.pdf "Celt Spoon."]
*Grand Illusions: [http://www.grand-illusions.com/acatalog/info_63.html ''Russian rattleback''.]
*Keath, Ed. [http://www.123too.com/ ''Turning a celt''.]
*Keltischer Wackelstein [http://www.wundersamessammelsurium.de/Mechanisches/KeltischerWackelstein "Celtic Wacklestein."]
*Krasnoukhov, Dr. Vladimir and Anatoli Kalinin. [http://www.jyuta.net/cosmo/vladimir/vladimir.html ''Stubborn Turtles''.]
*Pippard, A.B. [http://www.iop.org/EJ/abstract/0143-0807/11/1/112 "How to make a celt or rattleback."] ''European Journal of Physics'', vol. 11, pp. 63-4. Institute of Physics. 1990.
*Sanderson, Jonathan. Activity of the Week: [http://www.scienceyear.com/about_sy/news/ps_176-200/ps_issue182.html#4 Rattleback].
*Simon Fraser University: [http://www.sfu.ca/~closari/projects/ensc100/index.htm ''Rattleback''.] Engineering Science 100 Tutorial Group Nu. Burnaby, British Columbia, Canada.
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*Singmaster, David. [http://www.g4g4.com/MyCD5/SOURCES/SOURCE4.DOC ''Celts -- Rattlebacks''.] South Bank University. London. 2004.
*Toys From Times Past [http://www.toysfromtimespast.com/toys/stone.htm "Wobble Stone."]
*University of Cambridge Millennium Mathematics Project [http://motivate.maths.org/conferences/conf14/c14_talk1.shtml "Boomerangs and Gyroscopes."]
[[de:Keltischer Wackelstein]]
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