The faster a skater goes in a half pipe, the higher he can rise out of the pipe. To pump in a half pipe, the skater crouches down while riding across the flat bottom of the pipe, but must straighten up as he enters the sloped part of the ramp. Centripetal force, which keeps a body moving in a circular path (for example, a half pipe), makes it hard to rise up. The net work you perform by pumping to overcome the centripetal force though, gives you a net energy gain. This extra energy boost gives you the added speed and greater height at the top of the ramp or half pipe.
PUMPING IN RAMPS
Skateboarding in half-pipes requires a need for speed. The faster you go, the higher you can rise out of the pipe.
On flat ground, the conventional method for gaining speed is to push off with one foot.
But half-pipes present a much more elegant option for the speed-hungry skater. It’s called pumping.
To pump in a half-pipe, a skater first drops down into a crouch while traversing the flat bottom of the U-shaped pipe. Then, as he/she enters the sloped part of the ramp, called the transition, he/she straightens his/her legs and rises up.
By raising the center of mass just at the beginning of the ramp’s arc, the skater gains energy and thereby increases their speed.
From a physics point of view, the extra speed that comes from both kinds of pumping is a result of the equivalence of work and energy. As you move into the bottom the arc, centripetal force makes it harder than normal for you raise yourself.
The net work you perform in lifting yourself is equivalent to a net energy gain. This energy gain translates into extra speed and greater height at the top of the ramp.