Regina Barber (1:55)

So today on the show, we're learning the why behind the Winter Olympics. What fundamental physics principles are at work when a skier jumps or when a sled goes down a mountain. And how these world class athletes are using physics to their advantage. I'm Regina Barber and you're listening to Shortwave, the Science podcast from NPR.

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Regina Barber (3:51)

Amy There's a lot of physics to go over and I think the easiest way to learn all of these physics concepts is if we tackle one with each sport. So ski mountaineering, ski jumping and bobsleigh. So let's start with the brand new sport this year, ski mountaineering, ahead of its start on Thursday the 19th. What should our listeners know about the physics at play in this new sport?

Amy Pope (4:15)

So ski mountaineering, which they affectionately call ski mo, is a sport where the athletes are going to go up a 70 meter tall incline. Now, 70 meters is about 400 vertical stairs.

Regina Barber (4:31)

Oh my gosh.

Amy Pope (4:32)

So they are going to ski up part of this. Now, as you can imagine, if you think about skiing up a hill, that's not going to go really well for you.

Regina Barber (4:43)

It's hard.

Amy Pope (4:44)

Yeah. So these athletes have skins that they put on their skis. And so it's literally a fabric layer that's going on the bottom of their skis. Now these are going to be really unique because as the athlete slides their ski up the incline, it's going to have a very low friction, but as they try to slide it back down, it's going to have a high friction.

Regina Barber (5:08)

So these skins have like a different friction coefficient if it's like moving one way versus the other.

Amy Pope (5:14)

Correct. It's kind of like petting Your cat from front to back, it's a very low friction. It feel, feels good. But you try and rake the fur in the opposite direction and you're going to have a much higher friction. So it's actually going to grab.

Regina Barber (5:26)

And then at some point they no longer can like, ski up. Right. That skin on their ski isn't going to work anymore.

Amy Pope (5:32)

Right. So the skin on their skis is going to be very efficient. But once the angle gets too large, they have to take that off and they have to adjust their boots. So they were in an uphill mode and they have to change it now to a skill ski mode. And so now the boots become rigid and attached to the ski and our skiers are going to be able to ski down a course, much like you would see during a downhill ski event. So ski mountaineering is really exciting physics wise, because you are seeing athletes do something that is so out of the norm. We're no longer just using gravity to pull the athletes down to the bottom of the hill. But every other sport uses a chair lift to get you up to the top so gravity can pull you down. But with this, you're overcoming gravity and you are utilizing that friction in a way unlike any other sport to help you get to the top.

Regina Barber (6:32)

So with this new sport, we're dealing with, you know, defying gravity as we go up and really using it on the way back down. Let's talk about another sport that comes to mind that almost defies gravity a little bit and it's the ski jump. So that competition started last weekend and goes through Monday the 16th. Why is the ski jump so amazing to you?

Amy Pope (6:52)

Well, the ski jump is amazing because it really makes us think about how these athletes can stay in the air for so long.

Regina Barber (7:02)

It's like they're flying.

Amy Pope (7:03)

It's like they're flying. And in a way, they are. So there are two different hills that they jump off of in the Olympics. There's the large hill, which is like jumping off of a 50 story building. And there's the normal hill, which is like jumping off only a 30 story tall building.

Regina Barber (7:19)

Oh, no.

Amy Pope (7:20)

Just, just, that's it. As these athletes are jumping off. If you were to think about throwing a bowling ball off of this ski jump, it would exert a beautiful parabolic trajectory and it would land far short of where our athletes are going to land. So it would be much shorter. So what these ski jumpers are doing is, you'll notice whenever they take off, they assume a V position. Now with this V position, what they're trying to do is they're falling. Yeah.

Regina Barber (7:54)

And they're kind of like, closed up like a taco.

Amy Pope (7:57)

Yeah, they're closed up like a taco or flat like a pancake. And what they're trying to do is they're trying to minimize and maximize at the same time, their interaction with the air resistance. So you can imagine throwing your hand out the window of your car as you're going down the highway, and you can feel that air pushing against your hand. And so they have the drag, which is the air that's rushing face on at them. And so if you put your hand parallel to the ground, you're going to find that you can kind of fly your hand there. And so they're trying to use that air, those air particles as they're falling to help create a lift, which is a force that prevents them from falling in the downward direction. It's going to slow that motion.

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Yeah.

Regina Barber (8:45)

It makes me think of, you know, planes. When I used to teach Physics 101, I'd be like, okay, this is how plane wings work. And you take this, like, sheet of paper, and you'd blow air over the top of the sheet of paper, and the paper goes up. And this kind of amazes the students. And it's because this moving air has less pressure. And by moving air above the paper, you're generating lift underneath.

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And.

Regina Barber (9:08)

And these ski jumpers are doing the same thing. They're utilizing lift, right?

Amy Pope (9:13)

Exactly. So these ski jumpers are working very hard to maintain this optimal angle of attack, holding their body and their skis in exactly that same shape, so that they can minimize the drag but maximize the lift.

Regina Barber (9:28)

So in this last year, there've been a couple of ski jump scandals. First, there was this extra material that had been stitched into Norway's men's teamsuits. And then we. More recently, there are these allegations that male jumpers are injecting their penises with hyaluronic acid. And people were in this uproar because it could be giving these athletes an advantage, sticking to stitches, you know, of in the suits. How would extra material let you go further in a ski jump?

Amy Pope (9:56)

Well, it's actually really interesting whenever we look at how this extra material is going to help these athletes. So what we're going to find is that the lift is proportional to the surface area. So by adding in a small amount of fabric, we're actually adding in an area. And the larger that area, the larger the lift. The larger the lift, the greater time they're in the air. And the further distance these athletes are going to fly. It's kind of like these athletes are wearing a wingsuit.

Regina Barber (10:30)

Yeah, like a flying squirrel.

Amy Pope (10:31)

Yeah, exactly. They're capturing that extra wind.

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Wow.

Amy Pope (10:35)

Now, the other thing that happens is that they had these extra stitches that put in, so they actually put in an extra seam, and that extra seam made the fabric stiffer at that point. Now, that means that the material isn't going to flutter. So there's going to be a consistent area that's going to be exposed to the air. And these ski jumpsuits have to conform to the body really well. But the area with the most leeway is that anterior crotch length, which has the greatest tolerance, which is why they chose to add the material in that area. Everything else has to be so form fitting to the body.

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Wow.

Regina Barber (11:16)

I'm so glad we brought you on for this. I've been hearing so much about it. But for our last physics lesson, let's actually review conservation of energy. One of my favorite things through the bobsleigh competition. So that starts Sunday, the 15th. Let's imagine going up a snowy hill. You're gaining potential energy. So that's what we physics professors also call, like, stored energy. Then if you sled down, that stored or potential energy converts to kinetic energy, which is this moving energy. And when we're looking at the bobsleigh competition, it really does, like, tell you so much about conservation of energy. Why is that whenever you're looking at.

Amy Pope (11:57)

The bobsleigh competition, you are finding that you have a race that is decided by hundredths of a second? Okay. The entire race takes about a minute. And so there are several parts to it, because as we have our runners, our athletes getting into the bobsleigh, they have to run as fast as they possibly can. And that is because they want to maximize their kinetic energy or the energy of motion at the top of the hill. All of the bobsleighs start from the same height, so our athletes can have a small advantage by actually having a slightly larger initial speed. So as these bobsleighs go down the track, they're getting faster and faster and faster. So they're gaining that kinetic energy.

Regina Barber (12:46)

Yeah, I. I think a lot of people don't know this. If you have the most speed at the very top, you'll go even further. So they, like, recruit runners, right? Like Olympic track runners?

Amy Pope (12:57)

Yes. Olympic sprinters. Yes. They love to have those on the team because they can go fast enough.

Regina Barber (13:04)

Amy, this is so much knowledge and physics that you kind of gave us great analogies. It makes me wonder, is there a physics like sports question a student has asked you that you still haven't been able to answer?

Amy Pope (13:18)

Oh, there's so many questions that I can't possibly answer. I often have students ask me questions that seem rather simple at the onset about why one athlete might have an advantage over the other or who's supposed to win this race. And these are questions that I really can't answer because there are different weather conditions that go in. There are material conditions that go in. There are just so many factors and we're not even talking yet about the skill of the athletes. So there are just a lot of things that I can't tell my students definitively how things are going to work out.

Regina Barber (13:54)

That's it's the pain of physics sometimes, sometimes we just oversimplify it.

Amy Pope (13:58)

Right? Absolutely.

Regina Barber (14:00)

Amy, thank you so much for talking to us today about the physics of the Winter Olympics.

Amy Pope (14:06)

Well, thank you. This was great.

Regina Barber (14:08)

If you liked this episode, give us a follow on the NPR app or wherever you get your podcasts. And you could check out our episodes on how extreme G forces affect Olympic bobsledders or our Summer Olympics episode on gymnastics. This episode was produced by Hannah Chin. It was edited by our showrunner, Rebecca Ramirez, and it was fact checked by Tyler Jones. Jimmy Keeley was the audio engineer. I'm Regina Barber. Thank you for listening to Short Wave from npr. We're just, we're just gossiping about physics, that's all.

Amy Pope (14:42)

Hey, that's what I do all day.

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