The curling arena is a sheet of ice 146 feet long and 14 feet 2 inches wide (approximately 45.5 x 4.3 metres), carefully prepared to be absolutely level and to allow the "rocks", as the polished granite 20 kg stones are called, to glide with as little friction as possible. A key part of the preparation is the spraying of fine water droplets on the ice to create what is called pebble. The pebble helps rocks slide faster, and the curling action of rocks changes during a game as the pebble evens out from wear.
On the rink, a 12 foot wide set of concentric rings, called the house, is painted near each end of the rink. The centre of the house, marked by the junction of two lines which divide the house into quarters, is known as the button. The two lines are the centre line, which is drawn lengthwise down the centre of the sheet, and the tee line, drawn 16 feet from the backboard and parallel to it. Two other lines, the hoglines, are drawn parallel to each backboard and 37 feet from it.
The curling stone or rock used in the game weighs approximately 45 lbs and has a special feature on the bottom. The bottom of the rock is not flat, but concave and the actual running surface of the rock is only 1/4 to 1/2 inch wide on the rim of the concave bottom. This small running surface allows the pebble applied to the ice to have an effect on the action of the rock. The rock is rotated as it is released. If rotated away from the body the shot is said to be an out-turn, and if rotated across the body it is an in-turn. On properly prepared ice the rock will move laterally in the direction it is turning, especially toward the end of its trip. The degree of curl depends on several factors, including the preparation of the ice and the flattening of common paths to the house during the game. Ice on which the rocks curl well is said to be swingy.
Curling is played between two teams of four. A game usually consists of ten ends. In each end each player on each team casts two rocks in turn, the players on each side alternating shots. The rock must be released in the middle of the sheet before the near hogline is reached (players usually slide while releasing their shots) and must cross the far hogline; otherwise it is removed from play. On each shot, two players are equipped with brushes or brooms with which they can vigorously sweep the ice in front of the rock so as to alter its trajectory or increase the distance of travel. A player in the house, either the skip (captain) or vice-skip (also known as the third), has the final say in deciding whether the sweepers should sweep.
Until four rocks have been played, rocks left in front of the house (guards) may not be moved by an opponent's stone. If they are moved, they are replaced and the opponent's rock is removed from play.
After both teams have delivered eight rocks each, the team with the closest rock to the target is awarded one point for each rock that is closer than the opponent's closest. The winner is the team with the highest score after ten ends.
Most decisions about rules are left to the skips. In tournament play the most frequent circumstance in which a decision has to be made by someone other than the skips is the failure of the skips to agree on which rock is closest to the button. An independent official then measures the distances.
Curling is most popular in Canada, but is played in other countries including the United States, Scotland, Norway, Sweden, Switzerland, and even Japan, all of which, with other countries, compete in the world championships. Improvements in ice making and changes in the rules to increase scoring and promote complex strategy have increased the already high popularity of the sport in Canada, and large television audiences watch frequent curling telecasts, especially the Tournament of Hearts (the national championship for women), the Brier (the national championship for men), and the women's and men's world championships. The Tournament of Hearts and the Brier are contested by provincial and territorial champions, and the world championships by national champions.
While Canadian bonspiels (tournaments) offer cash prizes, there are no full-time professional curlers. Curling survives as a people's sport, making its Winter Olympic Games debut in 1998 with men's and women's tournaments.
Curling probably does not take its name from the motion of the stones. In the early history of curling, the rocks were simply flat bottomed river stones that where sometimes notched or shaped. The user would have had little control of a rock and luck had more to do with a good shot then the motion of the stone. The origins of the word "curling" are not known. It was first used in print in 1630 in Perth, Scotland. One possible derivation is that it came from the old verb "curr" which describes a low rumble, a sound that is strongly associated with the game (curling is often called the roaring game). Nevertheless, today a rock which deviates from a straight line is said to curl.