Halfpipe
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Halfpipe_Snowboard.jpg
A halfpipe is a structure used in gravity extreme sports such as snowboarding, skateboarding, freestyle BMX, or inline skating. The structure is usually wood, although sometimes the surface is made of another material. Appearance wise, it resembles a cross section of a swimming-pool, and in its most basic form, it consists of two concave ramps (or quarterpipes), topped by copings and decks, facing each other across a transition. Originally halfpipes were simply half sections of a large pipe. Since the 1980's halfpipes have had extended flat ground between the quarterpipes and the original style halfpipes have become curiosities. The flat ground gives the athlete more time to regain balance after landing and more time to prepare for the next trick.
The attraction of the halfpipe lies in the fact that a skilled athlete can play on it for an extended period of time, using a technique called pumping, to attain extreme velocities, while expending relatively little effort. Large (high amplitude) halfpipes make possible many of the aerial tricks in BMX, in-line skating and skateboarding.
For winter sports such as freestyle skiing or snowboarding, a halfpipe can be dug out of the ground. In such cases the plane of transition will be oriented downhill at a slight percentage of grade to allow drainage of melt, allowing a rider to take advantage of gravity to maintain his/her speed. In the absence of snow, halfpipes of this type can be used by dirtboarders, motorcyclists, and mountainbikers.