Science Secrets of Curling – There’s Something to All That Sweeping

Curling became an Olympic sport in 1998. It’s an unusual sport to many.

The sport involves one player thrusting a huge “rock” or stone down a sheet of ice. Two other players sweep a path, guiding the rock to the center of the target called the “house.” At the end of play, the team with the most rocks near the center of the house is the winner.

Getting a curling stone from the start to the house is all physics. Force and friction is what makes it all work.

It all starts with a push out of a “hack.” The curler positions their foot to push out of the hack with a lot of force to accelerate with the curling rock. The curler’s force is then transferred to the rock.

Then the sweepers take over. The brush they use is made from a synthetic material that has a little abrasiveness. The objective of sweeping is to make the rock go farther and very slightly alter the rock’s path.

When curling began and was a sport outside, the brushes were used to remove snow and ice in front of the rock. When the sport moved inside, they discovered the brush did more than remove the snow. The brush also reduces friction between the rock and the ice.

Rapid back and forth sweeping motions generates heat, warming the ice and creating a melted water layer. The layer reduces friction and creates a path of least resistance for the stone to glide on easily.

Friction is reduced further by another characteristic of curling – bumps on the ice. Other ice surfaces have a very smooth texture, thanks to the Zamboni. In curling, the ice has pebble shaped bumps created by spraying water on the surface, then freezing it. The ice has a surface similar to an orange peel.

Instead of slowing the stone down, the bumps give less surface area for the stone to ride on. The points reduce the total surface area that the stone is sliding on. Less surface contact means less friction.

Another problem with smooth ice – a greater surface area where the stone touches the ice would create a seal or vacuum, slowing down the stone.

By eliminating the vacuum and riding on points, the stone rides more smoothly and will go twice as far.

The stone is 42 pounds of a particular type of granite that only comes from an island off the coast of Scotland. The granite is hydrophobic, meaning it resists water. It won’t absorb much of the melt water. Absorption reduces lubrication and slows the stone down.

As the stone slides towards the target, another team’s stone may be in the way. When the stones collide, another wonder of physics takes place. The stones transfer kinetic energy and momentum – the product of the mass and velocity– between them.

From the hack to the house, the stone travels on a path of physics to give spectators excitement with a bump.

Get more information from NBCOlympics.com and the National Science Foundation. Lesson plan available on Science Friction: Curling at NBCLearn.com.