Why does a curling stone curve

May 14, Mike McLeod. General industrial science tribology. Print this page Tweet. I agree We are using cookies to give you the best experience on our website. As the video shows, if you spin an object counterclockwise and slide it along a surface, it will curl to the right.

Spin and slide with a clockwise rotation, it will curl to the left. There's more friction at the front of the object than the back, because as it moves, it tilts slightly forward. That results in a curl from the opposite direction of the rotation. So with a clockwise rotation the stone curls to the right and a counterclockwise rotation results in a curl to the left. When you watch curling, it looks like the stone will go forever, even though it is not moving very fast.

On good curling ice, it takes 25 to 28 seconds from the time the curler releases it until it comes to rest at the other end. This is because the stones are not flat on the bottom. They are concave with a running band about five inches in diameter and a quarter of an inch wide.

Combined with the bumpy texture of the ice, very little of the pound stone is in contact with the ice surface. This creates high pressure that keeps the surface under the stone right on the edge between solid ice and liquid water, which reduces friction. Think about ice skating. The stones are made primarily from granite quarried in Scotland.

This increases contact pressure which lowers the friction of the stone with the ice. As a result, the stones travel farther, and curl less. The second way to control ice friction which is done during a game , is by having other players on the team "sweep" in front of the curling stone. The sweeping action removes any dirt or debris, but more importantly it also temporarily raises the surface temperature of the ice by a small amount. This reduces the friction between stone and ice, which causes the stone to travel further and curl less.

Different stages of the stone's travel on the ice may require different trajectory adjustments. For example, the sweepers can be strategically placed so that they are opposite each other, with the sweeper closest to the stone having the most influence on the friction between stone and ice. The sweeper closest to the stone has the most influence because the proximity of his sweeping action gives more time for the stone to travel on the swept lower friction surface before the ice re-cools and friction is restored to its previous higher level.

In addition, the side the closest sweeper is on can also have some influence on how much the stone curls. Interestingly, the curling stone tends to curl more near the end of its travel during which the stone slows down to a stop. One possible reason for this is because the thin layer of melted water on the contact interface is dragged around to the front of the stone due to the stone's rotation , especially during the final few feet of travel.

This effect causes the friction force F F to become even smaller relative to F B. As a result, the rate of curl increases in the final few feet of travel. Clearly, the physics of curling can become quite complex when one tries to account for all the factors that come into play.