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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", stops and reverses its spin to the preferred direction. This spin-reversal appears to violate the law of the 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. This makes the rattleback a physical curiosity that has excited human imagination since prehistorical times.〔"celt, n.2". OED Online. September 2012. Oxford University Press. 1 October 2012 A rattleback may also be known as a "anagyre", "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== 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 pronounced as "s") describes adze-, axe-, chisel- and hoe-shaped 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, Mass. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rattleback」の詳細全文を読む スポンサード リンク
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