Newton's First Law

Newton's 1st law states that an object will move with a constant velocity unless acted upon. This means that a object that is standing still will stay in place unless a force pushes on it. The concept of Inertia is the tendancy that and object stays at a constant velocity.

This applies to snowboading when a snowboarder drops into the half pipe. He accelerates until he reaches the bottom and his inertia carries him to the opposite side of the half pipe so that he can do his trick.