Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why rocks curl

08.10.2004


One of sport’s greatest scientific mysteries has been solved, sort of. Two University of Northern British Columbia physicists have explained the centuries-old question of why a curling stone curls, or moves laterally, in a counter-intuitive direction.



The solution – published in the current issue of the Canadian Journal of Physics – isn’t an elegant equation of the kind mathematicians adore, say the scientists, but rather one that involved a lot of experimental sweeping. The explanation, nonetheless, could spark controversy at rinks – and even result in a new super-curl shot. "If you turn a glass over, spin it and slide it down a table it curls in the opposite way compared to a curling stone," says Dr. Mark Shegelski, an NSERC-funded UNBC theoretical physicist describing his post-game barroom demonstration of the problem. "The curlers think you’re doing some kind of magic, until they do it themselves and see that the glass goes the ’wrong way.’"

Curling is the indoor winter sport popularized by the Scots, and now an official winter Olympic event, in which two opposing teams slide and rotate smooth 20-kilogram (44-pound) ovals of granite (the stone) down a 28-metre-long sheet of ice. The goal is to get your team’s stones closer to the centre of a bull’s eye-style target than the other team’s.


Baseball curveballs and the trajectory of golf balls have long been the stuff of introductory university physics textbooks. But the reason for a stone’s curl, the very thing from which the game gets its name, has remained elusive. "The physics of friction on ice is considerably more complicated," explains UNBC experimental physicist Dr. Erik Jensen, the paper’s other co-author. Indeed curlers know that different ice surfaces can have an enormous impact on the stone’s movement; a skilled curler is able to "read ice" and anticipate the degree of curl. After a decade of theoretical exploration, Dr. Shegelski recently decided it was time for a scientific bonspeil to gather the experimental information needed to finally resolve the physics of the curl.

Drs. Jensen and Shegelski developed an experiment, and with the help of the staff of the Prince George Golf and Curling Club they were able to create an ice surface underlain with a detailed grid pattern. Using a suspended video camera they then recorded four hours of the widest possible range of shots, from slowly sliding rapid "spinners" to slow-rotation, high-velocity shots all thrown by three local curlers. The results are the first detailed quantitative measurements of curling stones’ behaviour.

So why does the curling stone curl the way it does? Wet friction, say the scientists.

"Our work makes a very convincing case that melting is inextricably involved," says Dr. Shegelski. "It doesn’t prove that there’s melting, but to explain our experimental results without invoking the existence of a thin-liquid film, well, I would be shocked if somebody came up with a successful theory that involved no melting."

This quasi-liquid layer – a microscopic slurry of ice and water "as thin as a bubble’s skin" – reverses the dominant frictional force on the stone. The glass on a table experiences dry friction, in which the largest frictional force is on the leading edge. So if it’s rotating clockwise, it will curl left. However, for the curling stone, the liquid layer reduces the friction at the front so that it is less than the friction at the back. Thus a clockwise-turning stone curls to the right.

Moreover, the only way to explain the extent of some of the extreme curls they observed, up to one-and-a-half metres of lateral movement, is that "the frictional force acting on each segment of the rock is directed opposite to the motion relative to this thin liquid film, and not relative to the underlying fixed ice surface," write the authors.

It’s an explanation that the physicists say has evoked cries of foul from some long-time curlers who insist they don’t see any water under their stones. The water layer is so thin it freezes too quickly to be observed when a stone is lifted.

However, the definitive theoretical explanation of the stone’s curl remains tantalizingly out-of-reach. Even though the observed curls and mathematical models fit closely, there’s still a gap, what curlers would call a biter. "At the end we punted and said we really can’t explain everything from first principles," says Dr. Jensen, now content to head back to his usual surface physics experiments with lasers.

But in pursuing his quest for curling’s ultimate prize Dr. Shegelski has inspired physics teachers across North America, and as far away as Germany, to take to the rink with their students. And, far from being purely theoretical, the latest experiments have paved the way for a new curling shot. Curlers are familiar with a shot called a "spinner," used as a knock-out shot, in which the stone is slid hard and rotated quickly so that it travels straight down the ice. "What we found is that if you really slow down the speed but maintain the high rotation rate of 70-to-80 full rotations, the stone’s curl is double that for a similar shot with five rotations," says Dr. Shegelski. "So that’s a cool thing that I didn’t expect to happen."

There could even be a new theory-inspired stone. On August 31st Dr. Shegelski obtained the Canadian patent for an idea entitled "Curling stone providing increased curl." But, after a decade of tangling with the curious curl, he’s remaining silent on this until the stone’s been tested.

Erik Jensen | EurekAlert!
Further information:
http://www.unbc.ca

More articles from Physics and Astronomy:

nachricht Pulses of electrons manipulate nanomagnets and store information
21.07.2017 | American Institute of Physics

nachricht Vortex photons from electrons in circular motion
21.07.2017 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>