COLD HARD SCIENCE.The Physics of Skating on Ice (With SlowMo) - Smarter Every Day 110

Hey, it's me Destin. Welcome back to Smarter Every Day. So in the Olympics, the most athletic team always wins, right? No. It's actually more complicated than that because there are physical objects in the Olympics. Now the team that is able to manipulate these physical objects better than the other team usually wins.

For example, curling. This curling stone is very heavy, and if you can figure out how to manipulate it across the ice better than the other team, you will win. So physics is a huge deal, and a knowledge of physics is very important. So today on Smarter Every Day, we're gonna start a three-part series on equipment used in the Olympics and how it interacts with the world around it. Today we're gonna focus on ice skates.

There are three major types of ice skates used in the Olympics: the figure skate, the hockey skate, and the speed skate. This is my new friend Glenn. He's a figure skating coach. It's really awesome. [laugh] So everyone already knows that angular momentum trick, right? So large moment of inertia, bringing it in. Small moment of inertia. That's pretty awesome.

So show me your skates. What makes you be able to do that? Cause I mean, I would mess up because of the toe pick, so where are you actually rotating?

(Glenn) "I'm actually spinning backwards. My blade is spinning backwards, and I'm spinning on a small area we call the ball of the foot. Also, my bottom toe pick is touching the ice. So it's allowing me to put forward pressure down without sliding forward like I would on a hockey skate."

(Destin) "So that's how you're able to keep from falling backwards?"

• "Right."

• "Yeah, I'm not really getting it. He's saying he's rotating about this point, but he's dragging that toe pick. Clearly, this is a good excuse to break out the Phantom."

Alright. OK, now this is making sense. You see, I used to think that they pivoted on one spot under the ball of the foot. Looks like I was wrong. They're actually skating backwards, and he's dragging that toe pick to maintain his balance. That's pretty cool.

Alright, it's time to move onto jumps. OK, Glenn's gonna show us three of the main jumps in figure skating. Here's the waltz jump, the salchow, and the flip. There's a gouge where you left the ice.

• "I pushed off my toe pick."

• "Pushed off the toe pick, and then there's another gouge..."

• "And I landed on my toe pick. But then I go down to my blade. So I'm pushing off the ice, and I'm landing on the ice, with my toe hitting first and then my blade."

• "OK, Glenn's gonna do a jump and he's gonna land with his toe pick, which is how they always land. It adds stability."

It's in the landing of these jumps where the design of the figure skates really start to show. You can spike yourself down into the ice with the toe pick, and then you slowly rock the blade down. In fact, the curvature of the bottom of the blade is called the rocker.

After it's planted firmly on the ground, you'll notice it doesn't immediately move away. The skater imparts the momentum from his opposite leg back into his lower foot, and then he moves. So it's a three-step process: spike, plant, move. Interesting.

But a question I have is that if the bottom is rounded, how do you sharpen a round blade? So this seems like a good opportunity to move from the figure skate to the hockey skate. So let's meet my friend Nick, who's the director of hockey operations at UAH.

[hockey sticks fall over]

So you want to show me... I'm sorry.

• "Second time."

• [laughs] "Sorry dude, show me the blade, how's this work."

• "So the blades here, if you look, it's two separate edges so I'll draw it up here for you."

• "OK."

• "Blade actually..."

• "So this is a cross-section."

• "Looks like that."

• "No way!"

• "A lot of people think it looks like that, but it's actually, there's a hollow in here."

• "Really."

• "Yep."

• "Can we see the sharpener? I like the name [wrestling announcer style] Blademaster!"

• "This is the wheel, which actually sharpens the skate."

• "How do you hold the blade up there? Is this a sled or something?"

• "Jig, slider, everybody's got their own little nickname for it."

• "OK, and so then if the wheel were turning, you would bring that in there... let me focus. OK, I can see that curvature that you're talking about, can you go closer if you would to the wheel?"

• "So that's the radius of the skate, 3/8ths, half, 5/8ths."

• "I'm not sure I understand. You're saying this hollow right here..."

• "Yeah, some of them will look like that, some of them will look like that, some of them will look like that."

This is completely eye-opening to me. I had no idea that ice skates had two different working edges. So why would a player prefer a deeper hollow vs. a shallower one? Well, think about it. If you have a shallow hollow, you're able to sit on top of the ice and glide very easily, so this is very good for speed.

But if you have a deep hollow, your points are gonna cut down into the ice and plow, so you'll go a lot slower; however, you'll get much better grip. And if there's one thing a hockey player needs, it's good grip. Have you ever seen them stop and change directions?

So I've asked a couple of hockey players to show me how this double edge is used to stop on ice.

Behold, the awesomeness of physics! [laugh] Isn't that crazy? Look at what he's doing. He's controlling that edge and scratching the top layer of ice off, but he's doing it in such a way that it's converting that shear energy into power, which he's using to decelerate.

Some people want to believe that hockey players are just dumb brutes, but I'm not buying it. I told this player I wanted him to stop on a very specific spot on the ice so I could zoom in with the phantom and catch the ice spray, and he did it on the very first try.

Can you imagine the math that's going on in his brain in order to automate this feedback loop? He's constantly sensing his deceleration, and somehow his brain's converting that information to signals to control the angle of his skates and feather the exact amount of ice that he's shearing off.

To complicate matters, he's got ice in between him and his target, and he has to anticipate the total amount of impulse left in that ice so he can stop exactly where he wants to. Let's ask him to see if he can explain exactly what he's doing because I'm pretty sure hockey players are physics geniuses.

You don't gotta take your glove off man. Ben, thank you very much. Do you have any, like if you had to say anything about that hockey stop, how exactly do you do it?

• "Well, you're just trying to find a balance because you have two, there's two edges on the skate blade, so you wanna find that inside edge. You know, if you get over the top of your outside edge, you go over."

(Destin) "So you're trying to find that edge on the ice and just shave a fine mist."

• "Just the inside one."

• "So like a noob, somebody that's just learning how to do that, would they just chatter across the ice?"

• "Yeah. When I started playing, I was like three years old, so maybe by the time I was like six I could stop."

• "Yeah."

• "So a couple of years, but like..."

• "Did you just hit that puck without looking?"

• "Yeah."

• "He just hit a puck and you hit it without looking."

• "I mean, I saw it."

Yep, I'm right, they're geniuses.

So if we want grip for a hockey blade, we don't want it for a speed skate, right? Which might explain why speed skaters are always falling. This was counterintuitive to me, but the bottom of a speed skate isn't pointy. It's actually a flat sharp 90-degree angle.

To see speed skaters in action, let's go to the Pettit National Ice Center in Milwaukee and check out the US junior long track championships.

OK, look at how the skater starts off the line. You see that open stance? They do this because ice skate friction is asymmetrical. They glide easily going forward but they dig in on the sides. So to propel themselves, skaters have to push off the sides of the blade. The larger this angle alpha is, the harder they can push.

That's why they line up with their foot at almost a 90-degree angle to the direction of skating. Speed skates are flat, which means each individual stride has to be perfectly level when the foot hits the ice. This can be a problem because when you extend your ankle, the blade tries to come up off the ice.

The solution to this is called a clap skate. Clap skates allow a long track skater to keep their blade on the ice longer into the stride. I'll let Adam explain.

• "The clap starts to come out, like this, and once they pick their skate up, it just kinda just flies back like that. And so that extra push that makes the clap gives you a lot more contact on the ice. And so you can get a lot more power."

All this talk about ice skating and we didn't even explain why it's slippery in the first place. So there's this thing called friction melting. If you're moving something along ice, it creates this really thin layer of water, think like nanometers thick. That is why you can slip on ice so easily.

The coefficient of friction can be defined by this equation. It's very interesting.

OK, a couple more things you might be interested in. Number one, we've been making infographics of all these winter sports. You can go download those and share them with whoever you like. Also, I'd like to thank the sponsor that lets me do crazy things like try to explain sports I don't really understand. So that's audible.com.

You can support Smarter Every Day by going to audible.com/smarter. You get a free audiobook, whatever you want, they've got thousands of titles. I used audible before they asked to be a sponsor for Smarter Every Day, so I'm more than happy to suggest that to you.

audible.com/smarter will get credit, and that'll help us move forward, do more crazy stuff like this. Speaking of more crazy stuff like this, if you would like to see more videos on winter Olympic sports, the next couple of videos, I'm gonna try to get them out pretty quick, are things like curling, and other stuff like that.

It's pretty cool. Anyway, support our sponsor, audible.com/smarter, and if you think we've earned your subscription, consider that please.

I'm Destin, you're getting Smarter Every Day, thanks for listening to me, I appreciate that. Have a good one.

Why are you putting your hands out all the time? Why do I always see figure skaters do that?

• "Because my coach told me to, over and over. It helps with my balance. Using my arms to rotate, turn myself. And to be a little more dramatic."

(Destin) [laughs] "You gotta have a little finesse to it, right?"

That's awesome. [Captions by Andrew Jackson] captionsbyandrew.wordpress.com Captioning in different languages welcome. Please contact Destin if you can help.