If you’re a surfer, you’re dependent on Mother Nature to let you glide along the watery curves. So what do you do when the surf is flat? Back in the 1950s, surfers – like the early amphibians of the Ordovician period – came onto land, taking the principles of surfing and attaching wheels to their boards instead of fins. But obviously the land is filled with many immovable objects not found at sea, such as gutters. And so the scene was set for Alan ‘Ollie; Gelfand to invent the most critical trick of physics in skateboarding in 1978: The Ollie.
To the onlooker, the Ollie looks like magic. The skateboarder jumps into the air and somehow, the board rises with them, as if glued to the feet. It is made all the more curious by the fact that the rider pushes downwards on the board to make it go up. How does this bizarre process function?
While coasting along the road, a rider must crouch, which lowers his or her centre of gravity. Simultaneously, the rider’s feet must shift so that the front foot is in the middle of the board and the back is planted firmly along the board’s rear. Just before the Ollie, the rider thrusts his or her centre of gravity upwards before his feet leave the board. This change in distance of the rider’s centre of gravity allows for acceleration. The greater the acceleration at this moment, the more height will be achieved with the Ollie.
As the body rises upwards, the rider then pushes down hard on the tail of the board. This exertion of force is greater than the force being applied by the front foot, which causes the nose of the board to rise upwards. A split-second later, the back of the board meets the ground. The ground then exerts an upwards force on the board relative to the acceleration it acquired on its trip downwards: This thrusts the board upwards into the air.
At this exact moment, the rider needs to move the back foot out of the board’s path by lifting it upwards. At the same time, the front foot can be edged forward. Given the current angle of the board, this will pull the entire board even higher. The force of the front foot acting in tandem with the rising tail will eventually cause the board to continue rotating tail-over-nose. Therefore, an equalising force must be applied by both feet. Ideally, this should occur when the board has reached its maximum height , after which gravity will take control. The potential energy that is gained from this height will convert to kinetic energy as the rider falls back to the ground.
It’s a complex set of movements and an amazing manipulation of various forces that allows a skateboarder to perform this relatively simple trick. This trick forms the basus of almost every other move in a skater’s arsenal, and it has even crept back into surfing. So next time you see a punk kid at the super-market clear a median strip, you can give an appreciative nod, before you apply a worrying grimace.— Chris Steado
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