In the Curling at the Olympic Games what is the purpose of the frantic ice brushing that goes on? Is it to slow down or speed up the stone or is it to try and alter the course of the stone?
I believe if you brush the ice you generate a bit of friction which in turn heats the top of the ice and a thin layer of water on top helps the stone to slide over the surface of the ice.
Sweeping After the stone is delivered, its trajectory is still influenced by the two sweepers under instruction from the skip. Sweeping is done for two reasons: to reduce friction underneath the stone, and to decrease 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 the 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 layer of moisture that builds up under the stone. One of the basic strategy aspects of curling is knowing when to sweep. When the ice in front of the stone is swept, a stone will usually travel both farther and straighter. In some situations, one of the two alterations in path is not desirable. For example, a stone may have too much weight, but require sweeping to prevent curling into a guard. The team must decide which is better: getting by the guard but traveling too far, or hitting the guard. Much of the yelling that goes on during a curling game is the skip calling the line of the shot and the sweepers calling the weight. The skip evaluates the path of the stone and calls to the sweepers to sweep as necessary to maintain the intended track. The sweepers themselves are responsible for judging the weight of the stone, ensuring the length of travel is correct and communicating the weight of the stone back to the skip. Some teams use stopwatch timing, from back line to the nearest hog line as a sweeping aid. Many teams use the Number System to communicate in which of 10 playable zones it is estimated the stone will stop. Usually, the two sweepers will be on opposite sides of the stone's path, although depending on which side the sweepers' strengths lie this may not always be the case. Speed and pressure are vital to sweeping. In gripping the broom, one hand should be one third of the way from the top (non-brush end) of the handle while the other hand should be one third of the way from the head of the broom. The angle of the broom to the ice should be so that the most force possible can be exerted on the ice. The precise amount of pressure may vary from relatively light brushing "just cleaning" (to ensure debris will not alter the stone's path) to maximum-pressure scrubbing. Sweeping is allowed anywhere on the ice up to the tee line, as long as it is only for one's own team stones. Once the leading edge of a team stone crosses the tee line only one player may sweep it. Additionally, when a stone crosses the tee line, one player from the other team is allowed to sweep it. This is the only case that a stone may be swept by an opposing team member. In international rules, this player must be the skip; or if the skip is throwing, then the sweeping player must be the third.
You can also influence the direction of the stone by frantically brushing one side or t'other. I'd give that Eve Muirhead some brush friction n'all, given halfa chance.
