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The sound barrier or sonic barrier is a popular term for the sudden increase in aerodynamic drag and other effects experienced by an aircraft or other object when it approaches supersonic speed. When aircraft first began to be able to reach close to supersonic speed, these effects were seen as constituting a barrier making supersonic speed very difficult or impossible.〔encyclopedia2.thefreedictionary.com/sonic+barrier〕〔http://www.oxforddictionaries.com/us/definition/american_english/sound-barrier〕 In dry air at 20 °C (68 °F), the sound barrier is reached when an object moves at a speed of 343 metres per second (about 767 mph, 1234 km/h or 1,125 ft/s). The term came into use in this sense during World War II, when a number of aircraft started to encounter the effects of compressibility, a number of unrelated aerodynamic effects that "struck" their aircraft, seemingly impeding further acceleration. By the 1950s, new aircraft designs routinely "broke" the sound barrier. ==History== Some common whips such as the bullwhip or sparewhip are able to move faster than sound: the tip of the whip breaks the sound barrier and causes a sharp crack—literally a sonic boom.〔May, Mike. ("Crackin' good mathematics." ) ''American Scientist,'' Volume 90, Issue 5, September–October 2002. p. 1.〕 Firearms since the 19th century have generally had a supersonic muzzle velocity. The sound barrier may have been first breached by living beings some 150 million years ago. Some paleobiologists report that, based on computer models of their biomechanical capabilities, certain long-tailed dinosaurs such as ''Apatosaurus'' and ''Diplodocus'' may have possessed the ability to flick their tails at supersonic speeds, possibly used to generate an intimidating booming sound. This finding is theoretical and disputed by others in the field.〔Wilford, John Noble. ("Did Dinosaurs Break the Sound Barrier?" ) ''The New York Times,'' December 2, 1997. Retrieved: January 15, 2009.〕 Meteorites entering the Earth's atmosphere usually, if not always, descend faster than sound. 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「Sound barrier」の詳細全文を読む スポンサード リンク
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