Pumping Up and Down while snowboarding.
 

In physics teacher mentioned that pumping helps snowboarders get more speed while going down a ramp, or the half pipe.

I'm wonderinf exactly why. Increasing friction would result in a loss of energy. I initially thought lowering the center of mass would increase centripetal force, but aparently they pump up and down...

I was wondering if someone else knew why snowboarders pump up and down.

Thanks,
ttl