Football has been rocked by the “Deflategate” scandal, swimming banned full-body “super suits,” and now the sport of curling—yes, curling—has its own raging controversy. Dubbed “Broomgate,” much of the fuss centers on a new kind of curling broom called the icePad, manufactured by Hardline Curling.


It’s not that the players are opposed to new technology in general; they’re just worried the icePad and similar high-tech equipment are altering the fundamentals of the sport in troubling ways by drastically reducing the level of skill required. The World Curling Federation temporarily banned the icePad for the 2015/2016 season, and is now considering new regulations to address this growing concern among players.

Caltech physicist Clifford Cheung about to throw a curling stone. (Image: Jennifer Ouellette)


As a game, curling is pretty simple—kind of like bocce ball on ice. One person on a team slides a heavy granite stone (or “rock”) down the ice. Then two other team members madly sweep the ice in front of the stone with little brooms, trying to get as close as possible to the center of a target area made up of four colored, concentric rings. The more you sweep, the longer the stone will travel and the less it will curl.

Sometimes you want it to curl, or don’t want it to travel as far. It depends on the initial throw. So the sweepers are guided by the “skip”: a player who watches how the stone is moving and instructs the sweepers on how to adjust their sweeping to keep the stone on the best trajectory. The teams take turns throwing eight curling stones each, per “end” (there are usually eight to ten such “ends” in a game). Whoever gets the most stones closest to the target center wins.

To understand why “Broomgate” is such a big deal, you need to delve into the physics involved in the sport. Mostly, it comes down to inertia, momentum, and friction—and the fact that, for curling purpose, the ice isn’t smooth, it’s “pebbled.” As I wrote for Scientific American in 2014:

Once a stone is thrown and gets some momentum, it can slide quite a long ways before the friction builds up enough to slow it to a stop. The better players can control the friction, the better they can control the curl of the stone as it travels down the ice and position it right where they want it in the house. The ice itself is special: the surface is sprayed with droplets that then freeze, forming a pebbled surface that reduces friction. as does a circular “running band” along the bottom of the stone — the only part of the stone that actually touches the pebbled ice, because the stone’s weight is concentrated on a very small area compared to regular flat ice. The frenzied sweeping with the little brooms helps reduce friction even further, slightly heating that segment of the ice very briefly before it refreezes. The stone curls more if you leave it alone. The point of the sweeping is to make the stone curl less and travel further. How much or how little you sweep depends on where you want to the stone to end up. There’s a lot more skill involved than you think, which is why the sport is sometimes dubbed “chess on ice.”


Why should the icePad make such a difference? Usually, the curling stone travels on top of the pebbled surface of the ice. Traditional brooms use foam or hair, which surround a given pebble and generate extra friction, making the sweepers work that much harder. In contrast, according to the Hardline website, the icePad “isolates the friction caused by brushing only where the running surface of the rock has contact with ice—on top of the pebble—with little resistance.”

That means sweepers have unprecedented control over the direction the stone is moving—maybe too much, according to many players. There’s a strong belief in the sport that it’s the players throwing the stones, not the sweepers, who should have the strongest influence on individual shots.


“It took a lot of the skill away from the throwers and put it in the hands of the sweepers and the person who was calling the sweep.”

“It took a lot of the skill away from the throwers and put it in the hands of the sweepers and the person who was calling the sweep,” curler Brad Gushue, a former Olympic gold medalist, told NPR. “It’s just allowed top players too much control to the point where it is actually difficult to miss some shots on the line.” And where’s the challenge in that? As another Olympic gold medalist, Ben Hebert, told the Ottawa Citizen, “When you throw a great rock, we want you to make the shot, and, when you don’t throw a great rock, I don’t think you deserve to make the shot.”


So the World Curling Federation held a “Sweeping Summit” a few weeks ago, whereby eleven top curlers and scientists from Canada’s National Research Council tested over 50 different curling brooms to determine their impact on the trajectory of the curling stones along the ice. Aided by lasers and a robotic stone thrower, the collected data will be analyzed and used to determine how the current regulations should be updated in light of these technological innovations. A vote is expected in September.

Maybe next the WCF can tackle the ongoing debate about why a curling stone curls in the same direction (rather than the opposite direction) that you spin it.

[Mental Floss]