Skaters seem to have found a way to defy the laws of physics, but they're actually using these laws to perform cool skateboard tricks.
The Physics of the Ollie
To perform an ollie, skaters jump over obstacles onto curbs and ramps. The coolest thing about this trick is that the skateboard seems to be glued to the skater's sneakers in mid-air. 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 Pumping in a Halfpipe
The faster a skater goes in a halfpipe, the higher he can rise out of the pipe. To pump in a halfpipe, the skater crouches down while riding across the flat bottom of the pipe, but must straighten up as he enters the sloped part of the ramp. Centripetal force, which keeps a body moving in a circular path (for example, a halfpipe), makes it hard to rise up. The net work you perform by pumping to overcome the centripetal force though, gives you a net energy gain. This extra energy boost gives you the added speed and greater height at the top of the ramp or halfpipe.
The Physics of the Frontside 180
Skaters perform the frontside 180 by flying into the air from the top of a halfpipe. When they reach the other side of the ramp, they seem to stay there for a moment, and then turn in mid-air and skate back down the ramp. This trick is performed by using the law of conservation of angular momentum. This law states that if you're rotating, you'll keep on rotating unless a twisting force stops you. Also, in the case of the frontside 180, if you're not rotating, you need a twisting force, or torque, to help you to start rotating. So, the skateboarderuses his arms as torque to turn himself around in mid-air, pulling off the trick.