Late Tuesday night, ginger-haired snowboarding phenom and controversial star Shaun White took home his third Olympic gold medal after completing insane back-to-back 1440-degree jumps on the Phoenix Snow Park. Those twin moves on Pyeongchang’s steep half-pipe — amounting to four revolutions in the air — are so difficult that even he had only completed them cleanly on the course earlier that morning.
Getting there required a precise interplay between the physics of his body and the engineering of the course. The pipe at Pyeongchang is built to Olympic standards, with the pipe’s slope measuring between 17 and 18 degrees and its length reaching the recommended measurement of 170 meters. The width of the half-pipe is between 19 and 22 meters, and the peak height of the wall is 6.7 meters. All of this is to say, this pipe is very tall and very steep. And for White, that’s a good thing.
The dimensions of the pipe are crucial to getting the amount of air necessary to complete four revolutions before touching the ground. The most crucial dimensions for such elaborate moves, explained Northern Illinois University engineering professor Brianno Coller in an interview with NBC in 2014, are the height of the walls and the curvature of the pipe because these are what allow a snowboarder to attain speed.
“Height is all speed,” he said. “If you can get that speed, you can get the height.”
Coller is referring to the fact that snowboarding is an exercise in transforming potential energy into kinetic energy. White’s potential energy is the energy he has by virtue of his position high above the pipe; his goal is to use gravity and exert his force against the sides of the pipe to convert that energy into kinetic energy, which is the energy of motion.
Anyone on a snowboard can stand at the top of the pipe and be pulled downward by the forces of gravity alone. But what separates great snowboarders from good ones is that the great ones can push back against the forces exerted by the side of the pipe (contact forces), thereby building speed. That’s what is happening as snowboarders pump their legs up and down on their way down one side of the pipe. It’s all meant to build enough speed to rocket off the edge and into the air.
Part of the reason White did his two big jumps near the end of his run is because that’s the point when gravity and technique combined have helped him reach his top speed — which in turn helps him get high enough to complete so many revolutions. As he’s coming down the slope, shifting direction on the half-pipe, Coller explained, he experiences centripetal acceleration. But for a rider like White, the force from centripetal acceleration can reach up to 2 G’s, which makes it a lot harder to gain speed as he shifts direction.
“The extra force that Shaun White feels just by going around that curve is about two and a half, 2.7 times his own weight. Shaun White has to carry his own weight plus the two and a half times his own weight just to pull himself through that turn,” he says. The ability to do so with ease is part of what makes White such an accomplished snowboarder.
Maximum speed attained, White clears the lip of the pipe. Once he’s in the air, he’s at his peak potential energy, but he needs to spin fast because gravity’s pull is reducing his mechanical energy. He did so — and then did the same jump again — converting the last burst of potential energy into blistering speed.
Skidding to a full stop at the end of a blazingly fast run, he held up his hands in triumph, having secured Team USA’s 100th Winter Olympics gold medal since the beginning of the games.