Why is sweeping in curling necessary? Isn’t the ice-sheet clean enough?
In: Physics
It is actually more polishing then sweeping. What they are doing is heating the ice through friction in order to melt a thin top layer into water. This water lubricates the ice making it even more slippery then ice alone. Once the stone have passed the water layer will freeze again so you need to do this again for each stone.
The purpose of the sweeping is to adjust the speed and direction of the stone. When you sweep harder, the ice melts and reduces friction.
Before the game starts the surface is sprayed with water, creating small bumps of ice where the droplets fell. This ~~increases~~ the friction on the stone.
By sweeping, the players are melting the bumps. They can make the stone go further or even slightly alter the trajectory.
Edit:
as u/hey_mr_ess has pointed out [it reduces the friction. ](https://theconversation.com/the-slippery-science-of-olympic-curling-we-still-dont-know-how-it-works-176463)
It might sound obvious to say, but curling shots curl. That is, you send the shot at a target, but it stops 4-6 feet to the left or right of the target. A curling playing sheet is also about 120ft from release to stopping point. You are looking to make the rock stop at a particular spot, 120ft down the sheet and ~5 feet from the target, and have a tolerance somewhere between 2 feet and 0 inches.
Sweeping changes how the rock interacts with the ice. Although the exact physical mechanism is unknown and somewhat disputed, the physical effect of sweeping is known. It makes the rock (1) slow down less quickly, and (2) depending on the angle of sweeping and the fabric of the brushes, curl (change direction) less, or (less frequently) more.
Sweeping controls the speed and the path of the rock as it travels. The sweepers can see most accurately how quickly the rock is traveling, and know where it *should* stop. So they want to sweep the right amount to get there. The skip (team captain; stationed on the other end) is watching the line (left/right travel). The skip and sweepers communicate how the rock needs to travel at different points along the shot, and might sweep more or less, or differently, to achieve the desired result.
Edit: I should add that the ice is *not necessarily* clean enough. Humans shed stuff all the time, and dust, hair, bits of rubber, or clothing fibers, settle on the ice. If a rock runs over one of those, it can “pick,” changing direction wildly and ruining the shot. If you hear a curler calling “clean!” they want the sweeper to brush the ice to remove any debris that could pick, but not so hard as to affect the rock strongly.
Edit2: Many people are saying that sweeping melts the ice. This is very probably not true. Melting ice requires a lot of energy and you’re not generating that much on a sweeping pass. You may be *heating* the ice a bit. You might also be making micro scratches on the surface that the running band of the rocks interact with. But you’re not melting it.
I always thought more sports should use “sweepers” like the javelin…maybe some guys down field with fans trying to get it further?
The shooter imparts rotation to the rock thrown.
The ice surface is “pebbled” which assists the rotating stone in it’s desire to “turn” rather than move in a straight line.
Sweeping creates a thin layer of smoother ice beneath the stone, reducing drag (stone slides further), and decreasing the amount of “turn” created by the rotation (stone moves straighter).
Same stone, thrown with same speed and rotation can be dragged more than 10 feet by good sweepers, if not more.
If you are interested in learning the physics behind curling, search on YouTube for “Smarter Every Day Curling” and you can find a very interesting video talking all about it.
it’s extremely difficult for the thrower to have the exact distance and direction to make a rock stop at a precise location. You are throwing from about 120 feet away from your target.
In high level curling, there are times where your shot needs to be very precise (within millimeters of target) to be useful.
Sweeping allows the team to control the rock to a certain degree.
There’s nothing that can be done if the rock is thrown too hard, but based on the sweeping technique used, sweeping could cause the rock to travel further down the sheet, travel straighter, or curl more than an unswept rock.
Good answers here already, but to make it simple: sweeping makes the rock go faster, not sweeping makes it go slower. Sweeping allows you to control how far it goes, even after it’s been thrown.
Sweeping makes a small change to the ice surface which changes the friction and influences the shot as it slides across the ice.
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