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A half-pipe is a structure used in gravity extreme sports such as snowboarding, skateboarding, skiing, freestyle BMX, and skating. The structure is wood, concrete, metal, earth, or snow. It resembles a cross section of a swimming pool, essentially two concave ramps (or quarter-pipes), topped by copings and decks, facing each other across a flat transition, also known as a ''tranny''. Originally half-pipes were half sections of a large diameter pipe. Since the 1980s, half-pipes contain an extended ''flat bottom'' between the quarter-pipes; the original style half-pipes are no longer built. Flat ground provides time to regain balance after landing and more time to prepare for the next trick. Half-pipe applications include leisure recreation, skills development, competitive training, amateur and professional competition, demonstrations, and as an adjunct to other types of skills training. A skilled athlete can perform in a half-pipe for an extended period of time by pumping to attain extreme speeds with relatively little effort. Large (high amplitude) half-pipes make possible many of the aerial tricks in BMX, skating and skateboarding. For winter sports such as freestyle skiing and snowboarding, a half-pipe can be dug out of the ground or snow perhaps combined with snow buildup. The plane of the transition is oriented downhill at a slight grade to allow riders to use gravity to develop speed and facilitate drainage of melt. In the absence of snow, dug out half-pipes can be used by dirtboarders, motorcyclists, and mountain bikers. Performance in a half-pipe has been rapidly increasing over recent years. The current limit performed by a top-level athlete for a rotational trick in a half-pipe is 1440 degrees (four full 360 degree rotations). In top level competitions, rotation is generally limited to emphasize style and flow. == Origin == In the early 1970s, swimming pools were used by skateboarders in a manner similar to surfing ocean waves. In 1975, some teenagers from Encinitas, California, and other northern San Diego County communities began using diameter water pipes in the central Arizona desert associated with the Central Arizona Project, a federal public works project to divert water from the Colorado River to the city of Phoenix. Tom Stewart, one of these young California skateboarders, looked for a more convenient location. Stewart consulted with his brother Mike, an architect, how to build a ramp that resembled the Arizona pipes. With his brother's plans in hand, Stewart built a wood frame half-pipe in the front yard of his house in Encinitas. In a few days, the press had gotten word about Stewart's creation and contacted him directly. Tom quickly formed Rampage, Inc. and began selling blueprints for his half-pipe design. About five months later, ''Skateboarder'' magazine featured Stewart and Rampage. 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「halfpipe」の詳細全文を読む スポンサード リンク
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