For the Olympics, the curling stones, which weigh about 20 kilograms, are traditionally made from a particularly water-resistant granite found on Alisa Craig, an island in the Firth of Clyde off Scotland. The bottom surface of the stones are made with a slight indentation, so each stone only glides on a thin ring, about one centimetre wide. Since the ring can only sit on a few rounded bumps of pebbled ice at one time, the contact with the ice surface is minimal and the stone can travel a long distance across the ice even at a relatively low speed.
When a stone is thrown, it is given a bit of rotation, which makes its journey more predictable. However, it also causes the path of the stone to bend – the curl. The reasons for this are subtle and have not yet been entirely settled by physicists. The standard explanation has to do with a downward force the stone experiences at its leading edge, similar to the force that pushes down the front end of car while lifting the back end when it brakes. In theory, this increases melting under the front of the stone, which allows it to slide more easily than the back. The difference causes the front veer to sideways in the same direction as the stone’s spin. In order to place the stone more precisely, sweepers brush the ice immediately in front of the stone. This raises ice temperature, which makes it easier for the stone to glide and tends to both lengthen and straighten a shot.
Editor's Note: The original print version of this article and an earlier online version incorrectly described what makes a rock curl. This online version has been corrected.
What to watch for in Sochi
Canadian curling teams are likely going into Sochi enjoying a relatively high comfort level with the curling facility there, in part because Canadian know-how has contributed to its design. As soon as teams arrive, they will begin by testing the stones, which are provided by the venue, to get a sense of whether there are slight differences in the weight and density that could slightly affect a throw, and therefore the order in which the stones will be thrown in during competition.
Steel blades on smooth ice
How it works
Speed-skate blades are longer and thinner than hockey-skate or figure-skate blades. The extra length keeps the skate in contact with the ice longer during each push-off and gives the skater more power per stroke. The thinness – about 1 mm – means the blade can slice through the ice more easily and doesn’t have to work as hard to push ice aside, like a tiny snow plow.
There’s also less of a rocker – the rocking chair-like curve at the bottom of the blade that in other skates makes it easy to quickly pivot and change. Since this isn’t required for speed skating, the rocker is shallower. The skate doesn’t dig as deep into the ice and so glides better. That also makes it harder to turn, but since speed skaters only have to turn in one direction, the skate blades are given a bit of a warp, or bend, to make them naturally want to turn that way.
Finally, speed-skate blades are flat ground on the bottom surface, rather than hollow ground. This minimizes the contact area with the ice and the friction still further, but it means that speed skaters have to keep their edges sharp otherwise they’ll lose their grip on the turns and take a spill.
What to watch for in Sochi
Speed skating is a fast as human can go without motorized or mechanical aid, reaching speed in excess of 50 kilometres per hour. More speed means more frictional heating and more melting of the ice under the blade. If the ice track is too warm to begin with, a faster skater will sink into the ice a bit more. If it’s too cold, the skates won’t slide as well because they’re not able to melt enough ice with friction. That’s why the ice temperature in modern indoor racing ovals is optimized for racing speed and kept at around -7°C, as it will be in Sochi.
With the ice already tailored for speed, the deciding factor in racing time will be air resistance, or drag. Like Vancouver, Sochi is at sea level, with a greater average barometric pressure than high altitude tracks like Calgary. High pressure means more air resistance, so while the competition is likely to be fierce at Sochi, it’s unlikely that world records will be broken there.