Why is sweeping in curling necessary? Isn’t the ice-sheet clean enough?
In: Physics
>Sweeping
>After a stone is thrown, players are allowed to sweep the ice in front of the stone. Sweeping clears the ice of any debris that might slow the stone down or send it off course. Sweeping also melts a thin layer of ice that reduces friction and thus increases the distance the rock travels.
>Sweeping is allowed by any player on the throwing team between the two tee-lines. Players are not allowed to sweep opponents stones in that area.
>Behind the tee line at the playing end, only one player from each team may sweep at any one time. This may be any player of the delivering team, but only the skip or vice-skip (third) of the non-delivering team.
>Only stones in motion – termed “running stones” – may be swept. Players may not touch any stones while sweeping. Also, they may only sweep in front of the stone, in a direction perpendicular to the direction of motion.
>Players are allowed to sweep stones that are set in motion by other stones.
So in short, no it’s not clean enough. Also it helps to melt a bit of ice. Sweeping helps a stone maintain speed and can be used to steer slightly.
After a stone crosses the tee line, a sweeper on the other team can sweep it too, trying to make the stone overshoot.
If your team manages to bump the other team’s stone, they might want to sweep it to make sure it doesn’t stop anywhere they’ll get points.
The curling ice sheet is pebbled. The friction of sweeping removes frost/liquefies an extremely thin layer.
Sweeping allows a degree of control over the stone. Sweeping reduces stone-ice friction so the rock will slow less quickly, and the stone will also curl less/travel straighter.
The ice is generally very clean, but relatively small bits of schmutz can have a pretty noticeable effect on the stone’s path, dragging and either leaving small scratches on the ice, or in more extreme cases catching between stone and ice and altering the path quite noticeably, known as “picking”.
Cleaning isn’t the primary reason for sweeping though. The path control mentioned above is the main reason.
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