is a wooden structure used in dry gravity extreme sports
such as skateboarding
, freestyle BMX
, or roller skating
. 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 rails and decks, facing each other across a transition. The attraction of the halfpipe lies in the fact that a skilled skater can play on it for an extended period of time, attaining extreme velocity, while expending relatively little effort. Large (high amplitude
) halfpipes make possible many of the aerial moves in extreme vertical skateboarding.
For winter sports such as 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, 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 during the "off season."