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The Science of Curling (Part 2)

Posted February 26, 2010 11:43 AM by Steve Melito

"Delivery is all about balance," explains Dion Warr, Vice President of the Schenectady (N.Y.) Curling Club. After pushing-off from the hack, a thrower "slides out behind the stone for a fair amount of distance". The curler's lead foot, clad in a shoe with a slippery sole, bears most of the weight of the body. The player, with forward knee bent and rear leg trailing behind, may slide as far as 20-feet before releasing the rock with a curl. Leg strength and abdominal strength are also important, Warr adds, and even casual curlers must be "firm and fit" to enjoy success on the ice.

Stones and Hog Lines

Curling stones are made of polished granite and have a circular running surface of just 4-inches in diameter. They also feature a detachable, molded plastic handle that the thrower grips with his or her dominant hand. Typically, a long-handled curling broom is used for counterbalance. After pushing-off from the hack, the player must keep the curling stone in front of the body and in contact with ice. The rules of the game require the curler to release the stone before it reaches the hog line, a boundary that resembles one of the lines in a hockey rink.

Clockwise or Counterclockwise

The curl that the thrower imparts before releasing the rock determines the stone's initial trajectory. Releasing the stone clockwise causes it to curl to the right. Releasing the stone counterclockwise causes it to curl to the left. Regardless of direction, Warr explains, the stone always has a rotation because it travels over a bumpy surface. "When we aim, we never actually aim at where the stone ends up," he adds. Rather, "we aim at a point and let the stone curl there".

Sweeping and Scrubbing

The faster a stone travels, the less its curl. When a stone curls too much, however, players minimize the amount of curl by sweeping the ice with a specialized broom. Traditionally, curling booms were equipped with wooden or fiberglass shafts. Today, Warr explains, "all the top players use carbon fiber shafts" instead. But shaft material isn't the only thing that makes a curling broom different from a commonplace kitchen sweep. In curling, the broom head itself is just a thin pad covered in Cordera, a synthetic material. Most players prefer a broom head that can swivel, Warr adds, "so that they can adjust the angle."

Pebbles, Pads and Particles

During sweeping, the curlers wear down the "pebble", the name given to the bumpy surface that distinguishes the curling sheet from the smoother ice preferred by figure skaters. With curling brooms in hand, sweepers push downward rapidly and repeatedly, scrubbing the ice with their coarse Cordera pads. "Good, powerful sweeping is really a matter of scrubbing the ice as fast as you can," Warr explains. But don't expect the ice to melt much – the players and their brooms don't produce enough heat for that. Curling creates "a microscopic slush of particles", Warr notes, but there's only a "small amount of melting" involved.

Friction and Lubrication

The pebble's phase change from ice to water (or at least from a solid to slurry) provides the moving stone with lubrication. On a ring, the force is the same in every direction. On a heavy curling stone, however, there is a "braking effect" at the front that increases the friction force there. With more of the melted ice moving towards the front, sweeping lets the rock glide on the ice and towards the button of the house - the curler's ultimate goal.

Editor's Note: Click here for Part 1 of this two-part story.


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Re: The Science of Curling (Part 2)

02/27/2010 6:23 PM

This is kind of poorly written, and raises more questions than it answers. Why are we told that "on a ring, the force is the same in every direction?" Does that explain something about why a heavy curling stone has "a 'braking effect' at the front that increases the friction force there?" If "sweeping lets the rock glide on the ice," why pebble the ice in the first place? Is it just to make the game harder, or is the sweeping used to steer the stone? None of this is sufficiently explained.

These little sayings down here are irritating. -- Me.

Join Date: Mar 2009
Location: Mid-West Ontario.
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Re: The Science of Curling (Part 2)

03/21/2010 2:03 AM

I have curled for 25 years starting in High School and mainly competitive after that. I have even played against both Russ and Glenn Howard teams. (almost beat them once with a 6~5 score) .

This is a sport that is much harder than it looks (or at least to be good). Much of it is hard to figure out unless you have actually played a few games or have even had an opportunity to step on or feel the ice.

Surface area is the answer to many questions. The rock is not flat on the bottom, it has about a 1/4 " ring around the outermost bottom of the rock, the inner is concave and does not touch the surface. Secondly the ice starts with a perfectly flat ice, like hockey ice but it is shaved (or called scraped) by a machine with kind of a chisel blade on it, this is sweeped up in preparation for the pebble. Pebbling is done by hand by a person carrying a can with a hose connected to a sprinkle head, he will walk backwards staring at the hack waving it from side to side trying to coat the ice evenly (sometimes the house to hog line is pebbled twice).

OK back to surface area. The rock rides on top of these pebbles of ice therefore there is very little contact surface between the ice and rock so this is why you see the rocks travel so far and so effortlessly. If there was no pebble, the rock would hardly move, or it would take much More force for it it move.

With forward momentum you would think the rock would want to go straight but that is not the case, this is where friction comes in, and when physics does too!

These are the main forces going on. Speed, rock rotation, friction;

SPEED, The faster a rock is thrown the straighter it will go (usually)

ROCK ROTATION, The rock will want to go in the direction you spin it. (but too fast of spin it will travel straighter and too little you can risk of a dead spin rock or it picking up the other turn)

FRICTION, By sweeping the ice you are keeping the ice clean (not really for dirt as the ice is usually pretty clean, less hair with new style brooms) but for frost. Sweeping hard literally polishes the ice and reduces the friction allowing the rock to travel further and straighter.

Melting is mentioned, yes it does although it is so minuscule it is not noticed. A pebble will last the whole 8 to 10 end game or 2~3 hours. (Even more technical is the water used) Soft water is recommended but even distilled water would likely be better. I remember my great uncle use to run the curling club and used water from the river, I also hear he sometimes put in soap!

So with all of you knowing a bit of science behind the curling, it is time to go out and put your knowledge to the test. Oh did I mention this is a very social sport too! Drinking is almost customary!

Cheers! Josh.

~Good Judgement comes from experience... and a lot of that comes from Bad Judgement! ~The Early bird may get the worm.. But the second mouse gets the cheese!
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