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March 12, 2010

Strange But True!

Q. In the winter Olympic sport of curling — think shuffleboard on ice, with four members on a team — a 42-pound banded stone is sent sliding over an ice rink toward a target region. The stone starts out going straight but curves gradually to one side, increasing near the end. What's the point of this “curl,” and how is it done?

A. Skilled curlers use it to finesse their stone around other stones that might shield the target, says Jearl Walker in “The Flying Circus of Physics.” This sideways deflection comes from the friction between the stone's narrow circular band and a thin layer of liquid water melted from the ice. Due to the stone's spin, the speed of the band varies from point to point, causing variable friction and deflecting the stone. This uneven friction also accounts for the stone's behavior at the end of its glide, spinning around one side as if pinned there.


 
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