COLD HARD SCIENCE. The Controversial Physics of Curling - Smarter Every Day 111

Hi, it's me Destin, welcome back to Smarter Every Day. In the last episode I explained that it's not always the most athletic team that wins in a sport, sometimes it involves physical manipulation of objects, so sometimes it's the smartest team. So today, on Smarter Every Day, let's take a look at the

physics

of

curling

. Well, before we look at some curlers, we need to learn the basics of the sport. This is the

curling

sheet and the circles are the house. The goal is to get your team's stone closer to the button. There are four people on each team.

The bowler, the sweepers and the jumper who commands. Each team has eight stones to throw, so each person throws two. They alternate with the other team so a total of 16 stones are thrown. The last one is called a hammer, which is a big plus. Do you have any idea how

hard

it was to find a curling stone in Alabama? It is really difficult. Anyway, I know what you're thinking. Curling is like the caveman sport, right? I'm going to slide this rock on the ice and I'm going to hit another rock and we'll try to outdo each other.

But oh no, it's much

hard

er than that. In fact, there are so many things I had never considered until I took a closer look at how this works. For example, the simplest question of all. What makes a curling stone curl? Okay, let's imagine for a second that this isn't my coffee table, it's actually a curling sheet. So we know from watching TV that when a player is back here at the hack, that's where they start, and he pushes it towards the house where you are, which is the bullseye on the ice, while he spins it or turns it the opposite way.

The clock hands will curve in the direction of that rotation, right? Now my guess is that it has something to do with this, that it's called a treadmill. You'll see that the bottom of the curling stone is concave, but there is a circular friction interface that interacts with the ice. So we should be able to model a circular friction interface of a sliding object moving on a rigid surface, right? What is this, a glass. I'll take this circular object, place it on the low friction surface, push it towards you and rotate it, and wait for a curvature in the direction of rotation.

Let's try it. But I don't see that. Let's try this again. Leave this, push towards you, twist it, curl it. Here we go. No. It curves in the opposite direction. This is what has really confused scientists for a long time. That interface of a sliding rotating object in normal motion on a rigid surface behaves completely differently with normal objects than with a curling stone. Something magical is happening right here on this rock and ice running strip. Clearly the next step is to go get ice. Oh! I wet my pants. Let's try it again. Oh man. So the curling stone goes in the direction of rotation but the cup goes in the opposite direction, which I can understand because as it decelerates on the table it tries to tip over, causing more force on the front edge of the cup.

So when it spins, it pushes the table with its leading edge. That makes sense to me. So let's go to the Milwaukee Wisconson curling club and see if they can teach us something with groomed ice and skill, most importantly. - We're at the Milwaukee Curling Club. We are located at the Ozaukee County Fairgrounds. This club is the oldest continuous curling club in the United States. (Destin) Before a game can be played, the ice must be properly prepared, which is a

science

in itself. If a stone rests on flat ice, a lot of contact friction is created, causing the stones to run slowly.

Curlers use a complex technique called pebbling to decrease the friction of the stones on the ice. Deionized water that has been purified by reverse osmosis is sprayed onto the ice in a very specific way and allowed to freeze. Here you can see Jay pebbles in the ice by moving a sprinkler nozzle back and forth. You can't imagine the number of variables that have to be controlled during this process. Number of arm movements, how fast you walk, humidity, the height difference between the tank and the sprinkler, the water temperature, yes. He's pretty crazy. After pebbles, they use a blade to cut the top of the pebbles to create a smooth, even running surface.

Because there is more pressure on the top of the pebbles, there is more friction melting, causing less friction. Which leads us to sweep. Before researching curling, I thought that sweepers somehow increased or decreased friction on one side of the stone or the other and caused it to curve. He was absolutely wrong. Sweepers actually sweep to warm the ice and make it curl less. If you throw two stones exactly the same and do not sweep one but sweep the other, you will find that the sweep will go straighter and further. This is a scanning electron microscope image of a pebble on ice.

You can see that they have cut it at the top so that it is fresh. However, this is the image of a pebble after it has been swept. You can clearly see that there are grain boundaries where it melted when swept with a broom. That thin layer of water that forms acts as a lubrication barrier, reducing friction and allowing the stone to travel farther and faster. So this is where it gets interesting. So, we are trying to find out why the curling stone curls correctly. Then I look around and find international experts on the

physics

of curling.

I find the guy in Canada and I find a team in Sweden and I start reading all their articles. Turns out these guys aren't even close to agreeing. It's really interesting. In fact, they have never even communicated by voice. They are only communicated through a technical document. Fascinating. I called the guys on the phone and had an hour and a half conversation with both groups, trying to understand what exactly the mechanism is. Harald Nyberg of Uppsala University in Sweden explained something called scratch theory to me. Visualize a stone spinning and moving across the ice. Now think about the band that runs and what the scratches would look like as it runs down the sheet.

The edges of the running belt would form this really impressive overlapping pattern as you slide down. Swedish scientists say that because the rough areas on the back of the band have to jump over the scratches created by the leading edge of the band, this will induce a force on the back of the stone that will cause it to curve in the direction of the band. direction of rotation. . They claim to prove this by showing images of pebbles that have been scratched at an angle after the stone slid over them. They also did an experiment by scratching the ice very deeply with sandpaper at two angles and pushing a stone through the scratches without turning it.

Pretty convincing right? Not so fast. Dr. Mark Shegalski of the University of Northern British Columbia in Canada once threw a stone with a polished metal band that did not produce the same type of scratches. He observed that it curved like a normal stone when thrown on freshly granulated ice. Dr. Shegalski believes the mechanism is something called asymmetric friction fusion. When the stone travels over the ice, the friction heats the ice and melts it, creating that lubrication barrier we discussed earlier. He believes there is more frictional wetting at the front than at the back because the rock tends to tip over just as the cup did in our previous experiment.

Another possibility is that because the advancing side of the rock is moving faster relative to the ice than the receding side, it could be creating more lubrication. You can visualize this by looking back at the difference in contact patterns. This additional relative motion would create more frictional heat at the top, which would melt more ice. This water could then be carried forward by rotation and lubricate the leading edge of the belt more than the trailing edge. That forward tilt of the rock or water transport theory pushes the rock in the direction of rotation. Both scientists are convinced that their theory is the dominant mechanism that occurs at the back of the running belt.

But they agree that there is still a lot of work to do. Personally, I don't think any one theory can answer all the questions on its own. I think the definitive model could be a combination of both theories. Dr. Shegelski believes there may even be one or two more mechanisms at play here that would help describe the curling stone's mysterious movement. Who knows, what I do know is that the nations that have scientists researching the physics of curling are the same nations that most often have Olympic athletes on curling podiums. Hey, I have a big announcement here on the way home from work.

I'm not sure if you can tell, but these videos take a lot of time and effort. Yes, you can, you are smart. You know what I'm doing here. You know there are two different curling experts, right? And I consulted them both to get the best idea. Well, I have done the same with something else. Jack Conte of Patreon and Hank Green, co-founder of Subbable, have created two different platforms that content creators like me can use to try to generate support for what they do. Now the idea is that if you enjoy and give some kind of value to Smarter Every Day, you can voluntarily...

You can, I'm not saying you do, but you can voluntarily decide to help out with what I do. Anyway, you can go to any of these pages, Patreon or Subbable, and you'll find all kinds of different perks there. There are ways to communicate with me, there are signs, there are all kinds of things. Infographics. So Patreon is a per video model and Subbable is a per month model. Now I didn't know what would work best, so I contacted these two guys and decided to try it out for myself to see which one works best for Smarter Every Day.

Anyway, you can try them out and see which one works best for you. Anyway, I'll leave links to the Smarter Every Day Patreon and Subbable pages and if you'd be willing to support Smarter Every Day that would be awesome. It would improve my life because I can streamline my workflow and probably be a better parent because I could have a little more time. Anyway, I'm Destin. Thanks for even considering that. Subbable and Patreon, getting

smarter

every

day. I'll leave links here and in the video description. Bye thank you. You're trying this at home, right? Oh shit.

I just broke it. Don't tell me. In physics there is a principle called conservation of momentum, so if momentum is mass times velocity and all the curling stones have the same mass, one might assume that it is velocity that is conserved. For the most part, the forward speed of the stone just before impact will be equivalent to the forward speed of the system just after impact. This works for both the X direction and the Y direction. Since there is no lateral velocity before impact, the lateral velocity after impacts must equal zero. Isn't it great? captionsbyandrew.wordpress.com Subtitles in different languages ​​are accepted.

Please contact Destin if you can help.