Short Wave - The Physics Of Figure Skating

Episode Date: February 7, 2022

Triple axel, double lutz, toe loops, salchows — it's time to fall in love again with the sport of figure skating. The 2022 Winter Olympics in Beijing are underway, and today on the show, Emily Kwong talks with biomechanic Deborah King about some of the physics behind figure skating. Plus, we go to an ice rink to see it all in action. You can email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Triple axle, double luts, toe loops, Salcow. It is time, my friends, to fall in love again with the sport of figure skating. The 2022 Winter Olympics in Beijing is underway. The event is a tradition dating back to the great Olympic Games of ancient Greece. Every four years, athletes from around the globe come together to compete on the world stage. Growing up in the 90s, I was obsessed with Olympic figure skating, just mesmerized by the grace, the outfits,

the beautiful spins and jumps of the figure skaters. And when Michelle Kwan entered the scene, she was everything to me. Her skating would make me cry. And I can't speak for all Asian American girls, but watching Michelle Kwan skate felt like a personal victory. She just had that big sister energy. And I was so proud of her.

But as graceful as her spins are, as smooth as her famous change of edge spiral is. This level of figure skating starts with a strong foundation. The one before a single is okay, but you want to have as much time as doubles as you can. So today on the show, we travel to an ice rink. You're all doing triples one day, right? To better understand the physics that drives figure skating, the forces behind those spins and jumps.

And we ask an exercise scientist, are we at the limits of what's physically possible for the sport? You're listening to Shortwave, the Daily Science podcast from NPR. All right, so before the Winter Olympics, producer Thomas Liu and I went on a shortwave field trip to the MedStar Capitals iceplex outside of Washington, D.C. Good. All right. I like your alignment. I think we could still use a little bit more speed going in.

This is Rachel Navarous. She's a former competitive skater, two-time Puerto Rican national medalist, and a former cast member for Disney on Ice. She danced as Anastasia, one of Cinderella's Wicked Stepsisters. And you're falling over your right side, which means you're over your alignment in the air. Well, that's exciting. I don't mind. And the other voice you're hearing, that's Rachel's student, Katie Fader.

You're applying the corrections and you're falling over the right side. When you're rotating in the air, where are you supposed to be rotating? Right side. Okay. Yeah, exactly. So nice and tight. So the fact that that's where you're falling is not necessarily a bad thing right now. But now go expect to land it. You know how to do this jump. Falling, getting back up, it's a bit like life. Katie's only 14. And she's been skating since she was seven years old. Spins are one of her favorite things to do. And you know what drives a spin? The laws of physics. Professor Deborah King teaches biomechanics at Ithaca College. She's been studying. the movement of figure skaters since grad school. Let's get into the physics of figure skating. Sure.

How do you even start a spin? I read that something called angular momentum is essential to the spin, but also really any fancy move on the ice where you're changing your direction. What is that? Yeah, so angular momentum, some people might call it rotational momentum. It's momentum for moving around an axis. So when you spin, you're spinning around the vertical axis that's going straight up and down through your body. And you want to just stay right in one place and just spin really fast.

So to spin, you need to create your momentum to move around that axis. And you do that by pushing against the ice and creating torque. Think about a wrench that you put on and you push against the handle. The longer the handle is, the easier it's to loosen the nut because you have more leverage. So when you push to go into a spin, the foot you push, you push. pushing with isn't acting right at the point you're going to spin. It's, you know, a little to the side. So that's like your lever. So you push off with, say, your right foot and maybe you're going to spin on your left foot. And when you start spinning, you have rotation momentum. I like this image of the wrench. It shows how you need to apply torque to your body to really reach out

and give your body the biggest kick you can to get that spin started. We saw this at the rink with Rachel. Who can spin really fast? And I love that moment when a skater, once they're in that circle, draws their arms in, like they're hugging themselves, and they start to spin super fast. And Deborah explained to me why. So when the skaters bring their arms in and they hug themselves, they're getting really small. So they're decreasing or making smaller their moment of inertia because all their mass is now really, really close together. That thing Deb just mentioned, the moment of inertia, is. really important to a figure skater. It describes how their body, their mass, is distributed

relative to the axis of their spin. So if a skater is spinning in a circle with their arms out, their mass is spread out and they don't spin as fast. But as they pull their arms in, their mass is more concentrated towards their center, their moment of inertia gets smaller, and they're spinning accelerates. Let's talk about jumps. Absolutely. You know, we watch it on TV. It's basically a spin where you leave the ice.

You know, unless you're doing like a split in the air, like a falling leaf or something, similar physics kind of applies in that you're rotating, but there's a lot of other stuff going on. What allows a skater to do a jump? So to get time in the air to actually do the rotation so you can complete your jump, that's going to come from the velocity you develop while you're still on the ice before. take off. As they're skating into the jump, they need to develop force as they push off the ice, and they're going to generate vertical velocity. That upward velocity from pushing off the ice determines their height. So the skater is essentially a projectile in the air. And once they're in the

air, they are going to follow a nice arc through the air, and they can't change that arc. So however much velocity they generate as they're jumping, that's going to determine the shape of their arc. and they have to get into that rotating position really fast and really tight if they're going to want to complete, say, a triple or a quad jump. We saw this with Katie. It took her a minute to get the right speed and the right angle into her jump. But once she had it, she nailed it. Good.

Okay. Now, a single or a double jump is one thing. But a triple or a quadruple, so three or four rotations, is another. What does it say about the fact that a quadruple axle is so hard to land? Period in competition. Are we kind of at the limits of figure skating, like where physics wins and you just can't push it anymore? Yeah, I think the quadruple axle and moving to quince. Like five rotations.

Yeah, you got it. Are probably reaching the limits of physics for humans figure skating unless for some reasons there were some major role changes. And, you know, you can start using and someone designs some equipment, which gives you extra, you know, force production so you can jump higher than you normally can and stuff like that. Skating the way it is now, you know, normal skates and just the abilities of the human body when you're, you know, trained optimally, there is only so much height you can expect a person to be able to get. And there is, you can only get your moment of inertia so small because that is determined by your body size.

You can't shrink your shoulders in more than whatever your shoulder width than your hip width is. So there are actual physical limits that we as humans can hit. So if you can't increase your rotation speed much anymore, the only other place is going to be getting more time in the air, but you can only jump so high. You can only jump so high. But let's be honest, the height that the human body can reach on ice is extraordinary. Think about it when you watch the Olympics this year. With years of training on the ice and off, these skaters went from balancing on a metal blade, about an eighth of an inch thick, to a triple axle. And while it takes an elite athlete to do the kinds of moves you see on TV, Rachel Navaris has seen bodies transform before her eyes.

One of her students is in her 70s and loves the sport of figure skating. What has skating taught you about the human? body. Oh my gosh. Your body, the bodies of other people. Right. Your students. Yeah.

Like the human body. Yeah. Well, I'd say first off, it's taught me that our bodies, as well as mine, can do way more than I ever would have expected and that they can be trained to do the things that we do and how they can become so easy and second nature. And, you know, when I was talking about how we have to make it look easy, you know, like. people will comment like, oh, you make that look so easy. And I'm like, well, first of all, I hope after how long I've been on the ice that I do. And also, you know, putting in the time. But in terms of just what I've learned about skating and bodies, whether it's my own or others in general, is how much of an effect those little things can make, such as height and, you know, muscle mass. And do I have kind of like quick twitch muscles or do I kind of move a little bit slower in space? and just how that relates to all of the skating moves. And just how no one skater is ever going to look the same, doing the same element.

And I think that's really cool. Rachel told me the number one thing people don't realize about figure skating is what a full body experience it is for the skater. How hard they're working out there. How tired their legs are. How nerve-wracking it can be. But that's okay with her. Because when all is said and done, there's a layer of artistry to those moments on the ice.

And hopefully, your audience will go on a journey with you. This episode was produced by Thomas Liu, edited by Jeff Brumfield and Regina G. Barber, and fact-checked by Catherine Seifer. The audio engineer for this episode was Andy Huther. Special thanks to MedStar Capital's Iceplex and Susan Flynn, friend of Shorewave, for helping us coordinate this episode. I'm Emily Kwong, and you've been listening to Shortwave, the Daily Science podcast from NPR.