Curling

I’ve written about the science of skating, and before that about the science of tobogganing. Now let’s look at a third winter sport, the one that’s hardest to explain to your relatives in Texas: curling.

Curling apparently originated in Scotland, probably starting with people tossing small rocks at targets on frozen lakes and rivers, like a wintry version of quoits. Boulders, and sliding rather than throwing, came along later — but still a long time ago: the first identifiable curling stone, found in Dunblane, Scotland, dates to 1551.

Curling came to North America in the early 19th century and was standardized in 1838. And wherever it started, there’s no doubt that today the real hotbed of the sport (or maybe I should say the “coldbed,” considering it’s played on a sheet of ice) is Canada.

Curling is a fascinating interplay of force, friction and momentum, based on the fact that it’s easy to slide things on ice. In the case of curling, that “thing” is a round piece of polished granite, concave on top and bottom, 91.4 centimetres in diameter and weighing 19.3 kilograms. (Oh, what the heck, call it 36 inches and 42.5 pounds. Curling, with its target circles 12, eight, four and two feet in diameter — definitely NOT 3.4, 2.4, 1.2 and 0.6 metres — is one sport that just doesn’t lend itself to metric measurement.)

Just like a toboggan or ice skate, the curling rock slides because the pressure it exerts melts the ice beneath it, creating a thin film of water that lubricates its passage. The player’s goal is to balance the energy he imparts to the rock with the friction of the rock on the ice, so that friction will win just when the rock is where he wants it to stop.

Curling would just be called “sliding,” however, if not for the fact that the rocks are made to curl, or curve, as they move down the ice. This enables a talented player (as opposed to, say, myself) to make complex shots such as placing one rock behind another.

When the player throws a rock, he turns the handle one way or the other, causing the rock to spin. The leading edge bites into the ice, imparting a little bit of sideways motion to the rock. Initially much of this curve is masked by the forward momentum, but as the rock slows, the sideways impetus becomes more noticeable, which is why the rock curls the most at the very end of the throw, just before it stops.

To maximize the “bite” of the rock into the ice, and therefore maximize control, you have to have increase friction between the two (unlike most other ice-sports, where you want as little friction as possible). That’s why modern curling is played on a pebbled surface, created by splattering hot water over the ice. On a smooth surface the curl would have much less effect and it would be much harder for the player to control the force of his throw, because much less force would be needed to get the rock down the ice, meaning any variations would have to be much more subtle.

Sometimes you’re not trying to carefully place your rock, you’re trying to knock out one of your opponents’ rocks. When one rock strikes another the energy the player gave to the first rock is passed on to the second. The thrown rock stops (or sometimes curls to one side, because the collision slows the spin less than the straight-ahead motion), while the target rock moves. However, it moves more slowly than the rock that hit it because some energy is lost in overcoming friction. Energy is also lost as a minuscule amount of heat and in vibrating the air to produce curling’s familiar “crack!” of rock on rock.

Unlike bowlers, curlers have some control even after their throw. Sweeping the ice just in front of a rock with a broom makes it travel faster and curl less. Sweeping melts the ice a little bit, decreasing friction, and removes any debris that might slow the rock. (Although the traditional corn broom can also add debris!)

Ice temperature is an important factor. If the ice is too warm, it will have too much water on the surface and will be very fast, making the rocks harder to control. If the ice is too cold, the rocks won’t slide well because they don’t weigh enough to melt it.

As you can see, there’s a lot going on in curling. Like golf, it looks deceptively simple, but successfully balancing all the forces at work takes a great deal of skill.

Even if your relatives in Texas don’t believe it.

Permanent link to this article: https://edwardwillett.com/1994/11/curling/

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