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In-Depth

Winning with Momentum

One of the most important elements of figure skating, the premier sport of the Winter Olympics, is elaborate spins.

Skaters start with their arms held out at their sides and bring them in, spinning faster as they do so. “It is like a merry-go-round. When you ride the merry-go-round, you walk toward the middle and you go faster. When the skater moves their arms inward while they’re turning their body, it becomes like you on the merry-go-round moving toward the middle. As you move toward the middle, there’s less of the body spinning. Since there’s less body spinning, it can spin faster, ” AP Physics teacher Philip Sumida said, illustrating the principle of the conservation of angular momentum.

Snowboard halfpipe is an Olympic event where stars like Shaun White glide back and forth from one side of a halfpipe to the other, while performing tricks and gaining amplitude. Sumida described how snowboarders like White performed difficult tricks like the frontside 1080 double cork. “What they are do is build up as much momentum as they can. It is pretty intense. White’s center of mass stays still, like any falling object. By keeping the center of mass constant, it means that he can use this energy to be able to increase his height. because what he wants to do is he wants to use all of his energy to lift up. He uses muscle to put a torque on himself, to give himself that extra height – that way he’ll go even higher the next time. He twirls around to conserve his angular momentum. If he can pull himself in, you can get really cool-looking fast turns. The hardest part is rotating around and keeping his center of mass in the same spot,” Sumida said.

“These Olympic athletes have crews of people telling them they need energy to turn a 100th of a second sooner, so they can get an extra inch higher. That’s what they practice, getting that extra inch, just enough to be able to clear [the next jump]. It’s pretty amazing. It’s really all about building extra energy and momentum. If you think about it, he’s just a big pendulum – a huge swing back and forth. When you use a swing, the place you want to pump is at the top. That’s when you want to throw your body back, and when you throw your feet back what you’re really doing is pushing your center of mass upward. The last thing you want to do is go side to side. When you do, you don’t go as high, because you use all your energy slipping. You’re trying to move yourself up because when you move yourself up you’ll fall further with more gravitational potential energy.”

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