Does sweeping in curling achieve anything?
February 20, 2010 3:16 PM   Subscribe

In the sport of curling, does the sweeping really do anything?

This question will probably offend all curlers (I am not one), but really . . . .

I speculate that in its origins on the wild rivers of Scotland sweeping was important, but with today's Olympic ice, etc. I'm skeptical that sweeping actually achieves anything. Scientific or research studies as references would be appreciated.
posted by feelinggood to Sports, Hobbies, & Recreation (19 answers total) 3 users marked this as a favorite
Well, according to Wikipedia's rules of Olympic curling which I read yesterday, it creates a thin layer of water which creates a sort of slick path for the stone to travel on.
posted by amanda at 3:23 PM on February 20, 2010

Sweeping cause a slight covering of water to form on the ice, and allows the stone to slide more easily. It the same basic principle that makes ice skates work.
posted by 517 at 3:23 PM on February 20, 2010

The ice is sprayed with water to make it uneven. Sweeping removes the bumps and allows for adjustments to speed and distance
posted by gregjones at 3:23 PM on February 20, 2010

Here's a description, to start
People who are new to curling, or unfamiliar with its nuances, are often puzzled at the fact that players wield brushes and sometimes sweep the ice furiously as the granite stone is delivered down the ice. It may look slightly odd but the sweeping is an integral part of the sport of curling. Indeed, I remember a very good curling player once telling me that a good stone in curling is one that requires to be swept. The rationale is that you have some control over where the stone will ultimately end up, so can increase your chances of getting the stone (or rock) to come to a stop exactly where you wanted it.

To understand why sweeping provides a degree of control, it's important to understand the role that friction plays in curling. There is friction between the ice and the underneath of the stone which means that a slightly underpowered shot will come up short. By vigorously sweeping the ice, the curlers can momentarily melt the ice. This lessens the amount of friction and this has two effects. Firstly, it reduces the speed of deceleration, meaning that the stone will end up going further than it otherwise would have. Secondly, it will cause the stone to stay to a straighter line. The stones curl most when delivered at a slow pace, so by maximising the stone's speed, the players can reduce the amount that the stone swings from one side to the other.

Here's some research (more in the link than copied below)
"Nobody is melting anything, even the best sweepers in the world. We looked at some sweepers who are built like linebackers and absolutely pounding the ice. They got it (ice temperature) up to maybe minus 1," Jenkyn said While sweeping doesn't melt the ice, it heats it up and the curling brooms absorb the moisture.

"We discovered pretty quickly that the wet broom head is far less effective than a dry, pristine broom head," he said. The advice for curlers: "Don't let those heads get wet, keep changing them up, keep them dry."

Jenkyn said the research showed sweeping is extraordinarily effective and the ability to heat up the ice is crucial.

While elite male curlers make 90% of their shots, women at the elite level are in the mid-80s.

"What we're thinking is the men at the elite level aren't necessarily better at shooting the rocks, they're better at fixing the mistakes," he said. "That's what sweeping is really doing. It's fixing the mistakes or adjusting the rock as you see how it is going down the ice."

posted by kch at 3:23 PM on February 20, 2010 [1 favorite]

If it didn't do anything, then you'd expect the Olympic teams to have figured that out by now and stopped doing it.
posted by EndsOfInvention at 3:24 PM on February 20, 2010 [7 favorites]

have you read the wiki page on curling?

"A key part of the preparation of the playing surface is the spraying of water droplets, called "pebble," onto the level ice. Because of the friction between the stone and pebble, the stone turns to the inside or outside, causing the stone to "curl".

and later, under "sweeping":

"Sweeping is done for two reasons: to make the stone travel farther, and to change the amount of curl. The stones curl more as they slow down, so sweeping early in travel tends to increase distance as well as straighten its path, and sweeping after sideways motion is established can increase the sideways distance. When sweeping, pressure and speed of the brush head are key in slightly increasing the layers of moisture that builds up under the stone."

so - because they aren't playing on smooth ice, they can't just slide the stone and expect it to go straight - the sweepers influence the direction of the stone.
posted by nadawi at 3:26 PM on February 20, 2010

In curling, the surface of the ice is not smooth; rather, it is pebbled by spraying a fine mist of water over the ice before play begins. Supposedly, the sweeping smooths the surface of the ice and coats it with a thin layer of water, which affects the speed and curl* of the stone.

Basically what everyone's said so far.

*If you watch a bunch of curling, you'll notice that every shot is taken with a twist to the inside or outside. This is the curl, and changing the speed of that enables you to place the rock more precisely where you want it to be along the width of the ice.
posted by malthas at 3:27 PM on February 20, 2010

@nadawl: not exactly on the last point I think - the "pebble" doesn't cause the curl by itself - the rock curls because it's been given a spin by the thrower - if they didn't put a spin on it, I think it would go in a good straight line.

My science-brain says that the pebble is there mainly to reduce friction and prevent any kind of suction-cup like effect between the rock and the ice... not to help the rock actually curl.

Maybe it's both?
posted by TravellingDen at 3:34 PM on February 20, 2010

I give you The Physics of Curling.
posted by Wild_Eep at 3:42 PM on February 20, 2010

From watching curling, it *looks* like sweeping does something -- the rock's path follows the (presumably lower-friction) swept area, even if the swept area curves (curls) around.

Here's a video from NBC on "The Science of Curling." It explains the deal with sweeping. Basically, sweeping melts the ice and smooths the ice's surface, which reduces friction; the swept path is the path of least resistance, so the stone follows it.
posted by sentient at 5:02 PM on February 20, 2010

I played a few weeks ago (=work team building in Montreal), and I can attest to the value of a good sweep!
posted by gillianr at 5:14 PM on February 20, 2010

Sweeping doesn't create a path for the rock to follow -- if it did so, it would imply that you could make a rock curl either more or less, both by sweeping harder, just on different sides of the rock, and that's simply not the case. Sweeping makes a rock run faster and straighter.
posted by jacquilynne at 5:35 PM on February 20, 2010

It's been 20+ years since I curled, but I seem to remember a shot delivered straight wouldn't go nearly as far as one delivered with curl. Sweeping also clears any random crap and frost out the way of the stone; less of a problem at the Olympic level, but in the decrepit old rink I used to play on (Crossmyloof) random bits of roof tile (or Canadian corn broom residue) could really ruin your game.

(The rules of modern curling have changed a lot with technology, and cheating Canadian bastards [I keed!] damaging the game with their slides. They probably don't even drink while playing ...)
posted by scruss at 6:42 PM on February 20, 2010 [1 favorite]

jacquilynne, you can make a stone curl a bit more just by sweeping just one side, the opposite one to which you want it to turn.
posted by scruss at 6:44 PM on February 20, 2010

I just had a curling lesson as part of a work group activity thing. The guy claimed you curl the stone for the same reason you rifle a bullet, to help it ignore imperfections in the medium of travel, in the case of a curling stone, ice. Sweeping is harder work than I expected, and made a significant difference, even in our untrained hands.
posted by nomisxid at 7:21 PM on February 20, 2010

Ok, it looks like there's an article in the Journal of Sports Science called The Sports Science of Curling: a Practical Review, which talks about sweeping. Article in full. Basically, the relationships between sweeping and curving and speed and so on are complicated. But, overall, science seems to think that sweeping does things.

The article includes some "key points:"

-Sweeping a curling stone can be highly physically demanding.
-Effective sweeping requires a combination of downward force and brush head speed, determined by the stone velocity.
-Sweeping on the left or right of a stone can help the stone to remain straight or curl more depending on the rotation of the stone.
-This can lead to the development of sweeping and playing tactics and contribute to team selection.

Also, apparently the pebbled surface makes the rock curve less than if the surface were flat.

Overall, the article seems like it addresses a lot of the issues, and includes references. (And diagrams and animations!)
posted by sentient at 8:10 PM on February 20, 2010

jacquilynne, you can make a stone curl a bit more just by sweeping just one side, the opposite one to which you want it to turn.

I was sort of ignoring that, but it actually supports my point, which is that the idea of 'path' is simply wrong. If you sweep only one side of the rock, it will move more in the opposite direction.
posted by jacquilynne at 10:16 PM on February 20, 2010

I guess I should emphasize that what I initially said about the rock following the path of the sweeping was just based on my observation of curling on TV, and the knowledge that the sweeping generally reduces friction.

The NBC video people did say that the rock is following the "path of least resistance," though, which seemed to lend support to my (incorrect) theory.

Maybe my assumption about the causal direction of the sweeping-path and rock-path was backwards. The rock naturally curls, so a curved sweeping-path is just used to decrease friction along the anticipated path that the (curving) rock would naturally follow. Or maybe I'm just totally wrong here. But, really, it looks like the sweeping path and the rock's path match, whether the path is curved or straight. Maybe I'm mis-remembering.

The article I linked to explains that the rock naturally curves in the direction of its initial spin (clockwise -> right, counterclockwise -> left). This is because, as it curves, the outer edge is traveling faster than the inner edge (just because of standard rotational mechanics), which means more heat generated on the outer edge, which means lower friction on the outer edge, and thus the rock ends up "pivoting" around the inner edge. So, if you do sweep near the inner (high friction) edge, friction is reduced there, making it a poorer pivot point, and making the rock curve less in that direction. Like you guys are saying.

I don't know though... if you're just sweeping a straight path/line in front of the rock (like how they initially seem to), you're reducing friction uniformly in front of the rock (right?), so shouldn't this just make the rock maintain momentum but curve to the same extent? (Since you're not upsetting the frictional balance between the inner and outer edge.) But the uniform sweeping I'm referring to apparently straightens the path of the rock (since it's not curving)... Weird. I guess, since the seemingly uniform sweeping evidently straightens the path, the sweeping couldn't actually be uniform. Perhaps the broom head angle or direction actually is creating asymmetrical friction, even if the whole area in front of the rock is being swept.

I gotta watch more carefully next time there's curling on.
posted by sentient at 10:18 AM on February 21, 2010

sentient: "I guess I should emphasize that what I initially said about the rock following the path of the sweeping was just based on my observation of curling on TV, and the knowledge that the sweeping generally reduces friction.

The NBC video people did say that the rock is following the "path of least resistance," though, which seemed to lend support to my (incorrect) theory.

I think you're missing the point: an object moving across a surface with uneven coefficients of friction will move toward the side with the highest friction.
posted by turkeyphant at 1:37 PM on February 21, 2010

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