Gravity is the engine that drives mountain boarding. If you place a mountain board on a slope, the force of gravity will pull the board down the hill at a prescribed rate of acceleration. The steeper the slope, the faster the acceleration is.
Friction is the force that keeps acceleration under control. As one object moves across another, friction acts in the opposite direction. Mountain boarding tires -- which are wide, thick and made of rubber -- are designed to produce a high level of friction, or traction, at all times. Good traction, even on uneven or loose road surfaces, is crucial to slowing down a mountain board, executing controlled turns and making sudden stops.
As a rider, the key to staying upright on the mountain board is to remain balanced over your center of gravity. The center of gravity is defined as the average location of the weight of an object. In humans, the center of gravity is in the hip area. To keep balanced, mountain boarders bend their knees slightly and hold their arms out.
To turn or steer a mountain board, riders rely on Newton's third law of motion, which states that every action produces an equal and opposite reaction. When a mountain boarder leans hard on his heels on the left side of the board, he is directing force to the right. According to Newton's third law, the ground produces an equal force in the opposite direction, pushing the board to the left. The net result: The harder you lean to one side, the sharper you'll turn to that same side.
For really sharp turns or aerial maneuvers, mountain boarders follow the law of conservation of angular momentum, which states: If you're not rotating, you need a twisting force, or torque, to get you going [source: Exploratorium]. To initiate a sharp turn, a snowboarder creates torque by twisting his upper body in the direction of the turn. This torque causes the legs to twist quickly in the same direction. The same torque principle is applied in aerial tricks to pull 180-, 360-, 720- or even 900-degree rotations.
Pumping is a trick mountain boarders use it to gain extra speed going up the ramp of a jump or to accelerate coming over a hump. When a boarder speeds toward a steep ramp and begins to ascend, centripetal force makes it harder for the rider to stand straight up. By pumping his legs and standing up at that moment, the rider creates a net energy gain. This gain translates into increased acceleration [source: Exploratorium].
Now let's take a break from the physics lesson and take a closer look at mountain boarding gear.