Forget the double touch, science doesn't know why rocks curl
National Post, 17 February 2026
There is something attractive in not knowing exactly how curling works
Olympic curling’s raging controversy, with Canadians in the unusual role of foul-mouthed villains, seems to have been put on ice. The special umpires summoned into action on Saturday to watch for the dreaded “double touch” were gone by Monday. The last time there was such careful attention to fingers on stone in Italy Michelangelo was sculpting the Pietà.
Curlers are already musing that all the attention might do the sport some good. When the Brier, Canada’s men curling championship, was last in Kingston, I bought tickets so my parishioners could attend all the matches over ten days. Outside Canada, interest is not quite so intense. But now allegations of cheating against the Canadians have made curling click bait! People were talking semi-knowledgably about the hog line.
There has even been attention paid to a matter which has heated up in recent years, namely the physics of curling. Serious scholars have tracked rocks from hack to house, and pronounced that — like the big bang and black holes and the nature of light and quantum mechanics — there is something of a mystery here. We know how to make the rocks curl — Canadians are amongst the best in the world at that — but we don’t know exactly why the rocks curl.
Some 40 years ago, when Bill Cosby was perhaps the most famous and admired man in the world who didn’t hold a prominent office — long before his serial sexual predation exposed him as fraudulent exploiter — he did a show at the Saddledome in Calgary, selling some 20,000 seats, unheard of for a comedian. Before getting to his regular jokes, he opened with 20 minutes of ad-libbed material, consisting mostly of him recalling how, after watching curling on television that afternoon at his hotel, he tried to explain to his wife on the phone what these Canadians were doing. Curling, then and now, is hilarious even for Canadians when seen through non-Canadian eyes.
At the Olympics the foreigners, as it were, join in the fun. It was even more fun in the 1980s, when corn brooms were still in use, and the thwack-thwack-thwack made curling as much an auditory experience as a visual one. I still remember Cosby, the master of vocal effects, mimicking the thwacking. Corn brooms were like a metronome set at top speed, matching the rising heart rates of a tense contest at a prairie bonspiel.
Physics killed off the corn broom, replaced first by push rooms made of hair, and now synthetic materials. They make for better sweeping, which helps rocks run farther and straighter, reducing friction on the ice by ever so slightly melting it ahead of the passing granite stone.
In recent years, the capacity to make ever-more precise measurements, including with electron microscopes, have made it possible to track exactly what is happening to the rocks to make them curl. Understanding has deepened, but questions remain.
The basic physics of curling depend upon the relationship of rotation and friction. If you slide a glass across a table, with a little spin, it will make a curving path, moving to the left if rotating clockwise or to the right when counter-clockwise.
The glass, as it moves forward, encounters greater friction at the front then the back, as it leans into the table. The greater friction at the front makes the glass curl to the left when spinning clockwise.
Curling rocks do the opposite; clockwise spinning goes to the right. Why might that be? The rock is on ice, not a table. Friction causes heat, which melts the ice at the front of the rock, meaning the greater friction is at the back — the opposite of the glass on the tabletop. So it curls the opposite direction.
Is the melting-friction explanation correct? That was the dominant theory in Canada, but about fifteen years ago researchers in Sweden proposed that curling rocks actually make miniscule scratches in the ice. In effect, the front of the rock scratches out a track that the back of the rock follows — hence the curl in the direction of rotation.
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