Use the up and down keys to make the skate boarder stand up or squat. Use the left and right keys to decrease or increase friction. The "pump" technique used in order to keep the skate boarder going up and down is to stand-up (up arrow key) when the skate boarder has high angular velocity (e.g. when approaching the flat surface) and to squat when the skate boarder has low angular velocity (e.g. when it is getting close to the top of the semi-circles, just before it starts to move in the opposite direction)
