Curling players sweep the ice in front of a moving stone to make it travel farther and straighter.

The longer version

A granite stone slides on pebbled ice, and brooms are worked across the surface just ahead of it. The friction briefly warms and smooths the pebble, which reduces drag, so the stone keeps more of its speed and travels farther. Sweeping also counteracts the curl, since a stone rotates slowly and drifts sideways as it slows.

That sideways drift is still not fully explained; a common account blames uneven friction between the leading and trailing halves of the running band, but experiments disagree. What is certain is that curl grows as speed falls, which is why late sweeping can straighten a shot. The ice itself is prepared by spraying water droplets that freeze into a textured surface.

Where this entry sits

Facts here look at the rules, equipment and odd histories behind familiar sports and games, from balls and rackets to cards, boards and playing fields. Expect small details about scoring quirks, stadium design and the long story of the Olympic Games. The full list sits on the Sports and Games page, where every entry is listed in order.