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

October 8, 2019

Hey it’s me Destin, welcome back to Smarter Every Day. So in the last episode I explained that it’s not always the most athletic team that wins in sport, sometimes it involves the physical manipulation of objects, so sometimes it’s the most intelligent team. So today, on Smarter Every Day, let’s take a look at the physics of curling. [music] OK before we watch 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 rock closest to the button. There’s four people on each team. The thrower, the sweepers and the skip who’s in charge. Each team has eight stones to throw, so each person throws two. They alternate with the other team so there’s a total of 16 stones thrown. The very last one is called the hammer, which is a major advantage. Do you have any idea how difficult it was to find a curling stone in Alabama? It is really hard. Anyway, so I know what you’re thinking. Curling’s like the caveman sport right? I’m gonna slide this rock on ice and I’m gonna hit another rock and we’re just gonna try to out-rock each other. But oh no, it’s way more difficult than that. In fact there’s so many things I had never even considered until I took a closer look at how this works. For example, the simplest question of them all. What makes a curling stone curl? OK let’s pretend for just 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, which is where they start, and he pushes it toward the house where you’re at, which is the bullseye on the ice, as he rotates it or spins it counter clockwise it’ll curl in the direction of that rotation, right? Now my assumption is that has something to do with this, which is called the running band. You’ll see the bottom of the curling stone is concave but there’s this circular frictional interface that interfaces with the ice. So we should be able to model a circular frictional interface of a moving sliding object on a rigid surface right? Which is this, a glass. I’m gonna take this circular object, I’m gonna put it down on the low friction surface, I’m gonna push it towards you and spin it, and expect a curl in the direction of rotation. Let’s give it a shot. But I don’t see that. Let’s try this again. Set this down, push toward you, spin it, curl. Here we go. No. It curls in the opposite direction. This is actually what’s really confused scientists for a really long time. That interface of a normal moving sliding spinning object on a rigid surface, behaves completely different with normal objects than it does with a curling stone. There’s something magical happening right here on this running band between the stone and ice. So clearly the next step is to go find us some ice. Ohhh! I wet my pants. Let’s try again. Oh man. So the curling stone goes in the direction of rotation but the cup goes opposite, which I can understand because as it’s decelerating on the table it’s trying to tip over, causing more force on that leading edge of the cup. So when it’s spinning it’s pushing against the table with its leading edge. That makes sense to me. So let’s go to the curling club in Milwaukee Wisconson and see if they can teach us something with prepared ice and skill, most importantly.
– We are at the Milwaukee Curling Club. We are located at the fairgrounds in Ozaukee County. This club is the oldest continuous curling club in the United States.
(Destin) Before a game can be played the ice has to be properly prepared, which is a science within itself. If a stone rests on flat ice it creates a lot of contact friction which makes the stones run slowly. Curlers use an intricate technique called pebbling to decrease the friction of the stones on the ice. Deionized water that’s been purified by reverse osmosis is sprinkled onto the ice in a very specific way and allowed to freeze. Here you can see Jay pebbling the ice by swinging a sprinkler nozzle back and forth. You can’t imagine the amount of variables that have to be controlled during this process. Number of arm swings, how fast he walks, humidity, the difference in height between the tank and the sprinkler head, the temperature of the water, yeah. It’s pretty crazy. After pebbling they use a blade to nip the top of the pebbles off to create a smooth uniform running surface. Because there’s more pressure on the tops of the pebbles, there’s more friction melting which causes less friction. Which leads us to sweeping. Before I researched curling I thought the sweepers were somehow increasing or decreasing the friction on one side of the stone or the other and making it curl. I was absolutely wrong. The sweepers actually sweep in order to heat the ice up and make it curl less. If you threw two stones exactly the same and you didn’t sweep one but you swept the other, you would find that the swept one would go straighter and farther. This is a scanning electron microscope image of a pebble on the ice. You can see that it’s been nipped on the top so it’s fresh. This however is an image of a pebble after it’s been swept. You can plainly see that there’s grain boundaries from where it melted when it was swept with a broom. That thin layer of water that forms acts as a lubrication barrier, reducing the friction and allowing the stone to travel farther and faster. So this is where it gets interesting. So we’re trying to figure out why the curling stone curls right? So I look around and I find the international experts for curling physics. I find the guy in Canada, and I find a team in Sweden and so I start reading all their papers. Turns out these guys are not even close to agreeing. It’s really interesting. In fact they’ve never even communicated with their voices. They only communicate via technical paper. Fascinating. I called the guys up on the phone and I had like an hour and a half conversation with both groups, trying to understand what exactly is the mechanism. Harald Nyberg at Uppsala University in Sweden explained something to me called the scratch theory. Visualize a stone rotating and moving down the ice. Now think about the running band and what the scratches that would make look like as it goes down the sheet. The edges of the running band would make this really awesome overlapping pattern as it slides down. The Swedish scientists say that because the rough spots at the rear of the band have to hop over the scratches created by the leading edge of the running band, this will induce a force on the rear of the stone making it curl in the direction of rotation. They claim to prove this by showing images of pebbles that have been scratched at an angle after the stone slides over them. They also did an experiment by scratching ice really deeply with sandpaper at two angles and pushing a stone across the scratches without rotating it. Pretty convincing right? Not so fast. Dr Mark Shegalski at the University of Northern British Columbia in Canada once threw a stone with a polished metal running band which doesn’t produce the same type of scratches. He observed that it curled like a normal stone by throwing it on freshly pebbled ice. Dr Shegalski believes that the mechanism is something called asymmetric friction melting. When the stone travels over the ice the friction heats up the ice and melts it, creating that lubrication barrier that we discussed earlier. He believes that there’s more frictional wetting on the front side than the back due to the rock tending to tip over just like the cup did in our earlier experiment. Another possibility is that because the side of the rock that’s advancing moves faster relative to the ice than the retreating side, it could be creating more lubrication. You can visualize this by looking back at the difference in the contact patterns. This additional relative motion would create more frictional heat up on top, which would melt more ice. This water could then be transported forward by the rotation and lubricate the leading edge of the band more than the rear edge. That forward tipping of the rock or the water transport theory pushes the rock into the direction of rotation. Both scientists are convinced that their theory is the dominant mechanism taking place at the back of the running band. But they agree however that more work still needs to be done. Personally I don’t think either one of the theories can stand up to all of the questions on its own. I think the ultimate model might be a combination of both of the theories. Dr Shegelski believes there may even be 1 or 2 other mechanisms at play here that would help describe the mysterious motion of the curling stone. Who knows, what I do know however is that the nations that have scientists researching the physics of curling are the same nations that most often have olympic athletes on the podiums for curling. Hey I have a huge announcement here on my way home from work. I’m not sure if you can tell but these videos take a lot of time and effort. Yeah you can, you’re smart. You know what I’m doing here. You know how there are two different experts for curling right? And I consulted them both to get the best idea. Well I’ve done the same thing for something else. Jack Conte from 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 if you enjoy and place some kind of value on Smarter Every Day, that you can voluntarily… You can, I’m not saying do, but you can voluntarily decide to assist what I do. Anyway, you can go to either one of these pages, Patreon or Subbable, and there’s all kinds of different perks on there. There’s ways to reach out to me, there’s posters, there’s all kinds of stuff. 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 both these guys and decided to test it for myself to see which one works the best for Smarter Every Day. Anyway, you can test them and see what works best for you. Anyway, I’ll leave links to the Patreon and Subbable Smarter Every Day pages and if you would be willing to support Smarter Every Day, that would be awesome. It would make my life better because I can streamline my workflow and probably be a better dad because I might have a little more time. Anyway, I’m Destin. Thank you for even considering that. Subbable and Patreon, Smarter Every Day. I’ll leave links here and in the video description. Thanks, bye. [laughing] You’re trying this at your house right? [Glass breaking] Oh [whispered] crap.
I just broke it. Don’t tell on me. In physics there’s a principle called the conservation of momentum, so if momentum is mass times velocity and the curling stones all have the same mass, you could assume that it’s velocity that’s conserved. For the most part, the forward velocity of the stone just before impact is gonna be equivalent to the forward velocity in the system just after impact. This works for both the X direction and the Y direction. Since there’s no sideways velocity before impact, the lateral velocity after the impacts has to equal out to zero. Isn’t that cool? [ Captions by Andrew Jackson ] Captioning in different languages welcome.
Please contact Destin if you can help.

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  1. Alabama? I would have put money on this being Canadian…… seriously, does any other country treat curling as a mainstream sport?

  2. Maybe it’s like some kind of increase in friction on the slower side since it’s not as tall as the cup it has no reason to try and tip over its already at its most stable position but the friction from the slower side combined with the inertia causes a harder pull from friction on that side causing it to turn

  3. Was the account of the stabilization of speed creates less drag thereby preventing an actual forward push on the center of gravity due to the continuation of the movement???  similar to when you are in a vehicle that is traveling at 60 mph and it isn't bouncing or swaying it doesn't affect your ability to walk across the surface?  With the decrease in the friction would also cause the momentum to be altered slightly due to the lack of stability in the curl itself thereby creating force in the opposite direction of the spin creating a reverse traction.  You stated that with the deceleration of the glass.  and with the pebbling it could also be causing a buffer in the front region of the curl momentum and causing somewhat of a cushion in the front of the vessel in the direction of movement.  You add in the drag being transferred more to the back of the vessel pulling back and to the left the vessel will move more to the right.  To understand buffer a little better you can research the difference between a conventional flat nose tractor vs the more aerodynamic versions ( and considering the shape of the stone itself it kinda fits the theory of forcing air into the lack of material in the pebbling.  And would also explain the slowing down of the stone and slower rotation due to the drag placed after sweeping ( moving in one direction and slowly changing the direction in the opposite direction doesn't happen instantly just literally slowing instead of changing until a certain rate of time )

  4. I keep meaning to ask; what is colorful light panel always hanging on the wall behind you? @smartereveryday

  5. my prediction is the the cup goes opposite because the cup its trying to tip forward so the friction is greater at the front pushing it agains the direction of spin. the same thing applies with the stone only the friction melts the ice making it water, lowering the friction so its pushed harder against the back edge

  6. I am no expert but this video is strange. If you don’t treat it as a solid rigid object but just fluid dynamics shouldn’t that explain it with basic Bernoulli? Like a spinning ball in the air or water?

  7. So, nobody's gonna mention how chad this guy looks by casually throwing a glass cup and catching it precisely on the bottom?

  8. Destin, I watched this video years ago when it came out. I've just watched it again, and I'm sat here wondering if you might be able to learn more by creating an experiment with a high speed camera, shooting from underneath, recording the interactions between a curling stone on a sheet of polyurethane which has been prepared with a thin coating of pebbled ice. It'd be incredibly cool to even find out if you could see any friction melting happening through the lens. Just a thought.

  9. I saw a video where a guy that makes various drones / rockets / cars tried to make a box that flew but was only stabilized by counter rotaton. Think, helicopter here, if the tail blade fails the helicopter spins because if the main blades centrifugal forces. Could that be what's happening here? I can't remember if it attempts to rotate the same, or opposing direction.also another minute factor (7:20) is the stones weight and friction on the leading edge creating a tiny lubricant barrier?

  10. The glass has way more friction and also top heavy so its putting way more friction on the leading edge cause its almost tipping over the whole time. A curling stone has a lover center of gravity and way lower friction. Has to have everything to do with it

  11. Get two curling ng stones. Put one in freezer for days, and keep one at 80 degrees Fahrenheit for days. Then try them and see what happens.

  12. 2:20 is just logically, the front of the glass (facing the camera) has more friction to the table than the opposite part, so (put in explaination here pls)

  13. watching you fall on ice was the funniest thing ive watched in awhile…and love that you had fun during lmao

  14. when socer players hit the ball the fut ball 2 b exact , and when the ball get hit from a certenangle goes in oposite direction , so the socer players r the best sientists ?

  15. Guys it's 5:30 in the morning.
    I haven't slept yet and have to go to work in 5 and a half hours…

  16. If I had to guess who thought and made this game I would say a canadian with too much free time that played a lot of billiards and darts at bars that had to travel from his home to the bar with ice skates.

    I also have a suggestion to make the game more interesting to watch. Make it so that the participants have to drink 1 bottle of vodka AFTER the game starts so they are forced to chug it, this way they have to drink daily to build tolerance to alcohol if they want to stay competitive.

    I'd watch that over any other Olympic game.

  17. What about the air moving over the top and around the shape of the handle relative to the wind. Wouldn’t there be a change in air pressure also effecting the spin and rotation ?

  18. Has anyone considered the buildup of liquid in the dip in the center with motion acting to build up a reservoir against the rear increasing the contact area of the fluid pushed across the ice under the inside of the dip, or the fact that the friction of the stone as it turns will change the shape of the trapped fluid, of course if the pebeling is sufficient to allow any melt water that is created in the dip to drain as it passes then it may be a mute point but i think it deserves investigation.

  19. couldnt you test the second theory about the rotation difference to the direction of travel by sliding two wheels to their direction of rotation. so you would have just the two | | contact surfaces without the ones parallel to travel direction.

  20. FRIGGING BLEEDING OBVIOUS that the velocity differential, due to forward motion, generates coincident frictional surface heating differential. There is obviously an optimum ratio between the rotational and forward velocities of a stone that will maximise the path curving effect.
    Seems THAT determination IS BEYOND the two incompetent 'so called experts' here sighted. especially as rudimentary 'computer motion modelling' would discover just that ratio.
    Wankers !

  21. By looking at this video, i just know that education in my country is still far from others. So sad 🙁

  22. So DO throw stones inTO the ice house, but DO NOT pass the hog line or burn your stone… GOT IT! ??

  23. wouldn't a curling stone transport the lubricating water down the edge of rotation causing more friction on the unlubricated edge causing it to have more force pushing it in the opposite direction of rotation so if the curling stone rotates clockwise it would curve to the left due to the right side of the curling stone being more lubricated and applying less force on the ice than the left side, causing the drag of the left side to pull it left.

  24. Seems like "sweeping" + the scratching of the surface= frozen waves pushing in the direction of gravity! Or is it the stones spin and turn in the direction of the scratches? I'm confused…

  25. This is going to be the sport that future human martians are going to play on mars…soccer and football andrugby and cricket simply wont be intellectual enough..

  26. So interesting, consider reading a paper or two cause i wonder if they have recorded it from underneath with flir and slow motion camera's 🙂 ….. science is better than ranting haha

  27. Your chann is just so addictive,it's very well made and the information you bring to each vid is incredible,are you a teacher,?! What is our occupation?!,just wondering.Yeah,so thank you for sharing your time and knowledge I do appreciate it…

  28. As far as subbable and patreon isn't there a way just to contribute when you want to? I mean do you have to sign up to constantly take money out of your check each month or per video . You should be able to say for instance this week I got a few extra bucks I'll chip it in. There's another Channel I tried to go on patreon and and it look like I had to contribute a certain amount of money per video and it was so confusing I just got out of it and never looked again. Thanks

  29. "In the direction of the rotation" is not descriptive enough. It is spinning in every direction simultaneously.

    Threw me off at first, because I imagined putting side spin on a pool ball, which has the opposite effect as curling.

  30. WTF does any of this BS have to do with creating better LIVING CONDITIONS!
    WHY do we give federal research GRANT MONIES to this BOGUS type of research? Absolutely RIDICULOUS!

  31. Id like to know would the glass act the same if it had alot of overhanging weight around the outside of the band making the contact with the table, like the curling stone.

  32. I've watched this video like 5 times. Curling is fascinating. I live in Kansas. No curling here but it's still interesting.

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