PHYSICS



Physics of the Ollie




Other forces used iin skateboarding

friction
gravity
motion
acceleration

The ollie is a basic move that all good skateboarders know how to do.

The physics behind the ollie is called rotation around multiple axes. Three forces act on the skateboard just before the skater jumps: the weight of the skater. the force of gravity on the skateboard. the force of the ground pushing up on the skateboard.These three forces balance out to zero, which is why the skateboard rolls along at a constant speed. The skater also needs to crouch down in order to do an ollie because a low center of mass is essential to jumping high.

The Physics of the Ollie



FORCES IN THE OLLIE

Just before a skater performs an ollie, there are three forces acting on the skateboard. One of these forces is the weight of the rider. Another is the force of gravity on the board itself and finally, there is the force of the ground pushing up on the skateboard.
These three forces balance out to zero. With no net force, the skateboard doesn't accelerate, but rolls along at a constant speed.

CROUCHING DOWN:

  • The rider's first step in completing an ollie is to crouch down low while riding on the board. The consequence of this is a lower center of mass, which will help give the rider more time to counter the forces of gravity and inertia.

JUMPING UP:

  • The rider pushes down on his skateboard, hard, and it pushes back with an equal and opposite force (remember Newton's laws?). The lower the rider's center of mass was before the jumping up phase, the better, because they then have more time to push of the skateboard, and they can create more of an equal and opposite force, and jump higher. The body of the skateboarder is a slave to inertia, just like other objects with mass. It naturally want to stay close to the earth, because gravity is pulling the rider down, and it requires less force to obey gravity than to try and counter it. But since skateboarders want to do this trick, we have to find some way to break the counter the forces of inertia and gravity. Jumping up after crouching down are the steps skaters take to counter these forces.

COMING BACK DOWN:

  • Once the rider is in the air, he/she has nothing to push off of, nothing to create an equal and opposite force to keep rising. Inertia demands that objects want to do as little work as possible. Soon, the upward forceforce decreases, and gravity stays the same, so soon, gravity is pulling down with more Newtons than you are rising with. The effect of this is that you start to fall back to the ground, safe and sound once more.

ABSORBING THE IMPACT:

  • When you land back on the ground you have quite a bit of force. The amount of force depends on the height of your ollie, and the air time. Landing from ollieing off of a roof would have more force than ollieing off of a picnic table. As we know, gravity pulls objects towards the ground at a rate of 9.8 meters/second/second. Therefore, the more time you are falling, the more force you have heading towards the earth. If a rider lands with straight knees and standing up tall, a large shock at the force of hitting the ground will ensure, and shock will go through the skateboard. Skateboards have been known to break if the rider does not correctly land a trick, especially off of high obstacles. The wisest method of spareing most of your body and your board the shock is to bend your knees when you hit the ground. This way, your knees (which are exceptionally strong, I might add) can take shock that would otherwise be headed for the rest of your body. The knees are like shock absorbers to a skateboarder.