Wednesday, January 05, 2011

The Physics Of Ice Skating

It's winter here right now in the upper Northern Hemisphere. So winter and winter sports are a common topic, and one winter sports that often get a lot of coverage is ice skating. This news article tries (that's the operative word) to convey some physics of ice skating. Inevitably, the central question whenever we talk about ice and ice skating is, why is ice so slippery?

The skate plays a role as well. The skating boot is equipped with a thin, slightly curved piece of tempered steel attached vertically to the exterior of the sole. This blade ensures that a minimal area comes into contact with the ice, reducing resistance in the form of friction.

The pressure of the blade on the surface of the ice also causes the ice to melt, producing a thin layer of water between the solid ice and the edge of the skater's blade.

"This layer of water gives you very little friction," said Dr. Harry Shipman, professor of physics and astronomy at the University of Delaware. "But if your balance isn't certain and your skates are wobbly, you're going to put more pressure on more layers of water, causing you to slow down. You have to manage the friction as much as you can."

There is a little bit of a perpetuating myth involved here, and this is a good time to deal with this. Many studies have been done in figuring out if the pressure exerted on by someone standing on ice skating blades can actually cause such melting[1,2]. I think this has been clearly debunked. In fact, one can even ask why is the ice still slippery even when one is standing still wearing regular shoes? After all, in such footwear, the contact surface area is considerably larger than skates, and here, it is very difficult to argue for pressure melting.

A very detailed review of why ice is slippery can be found in a nice article in Physics Today by Robert Rosenberg[3]. In it, he showed an interesting phenomenon of liquid-like layer on the surface of ice even at a temperature as low as -35 C. This liquid-like layer is the one primarily responsible for ice being slippery.

Again, common observation/phenomenon can create very interesting physics. That's why I love physics!

Zz.

[1] S. C. Colbeck et al., Am. J. Phys. v.65, p.488 (1997).
[2] S. C. Colbeck, Am. J. Phys. v.63, p.888.
[3] R. Rosenberg, Phys. Today p.50, December 2005.

4 comments:

sudheer s. said...

almost everybody has the same reason for slippery nature of ice-the skater exerts pressure and the ice melts ,the skaters glides on the layer of ice-your post atleast debunks the idea.Thank u.

John Wang said...

With regular shoes, the pressure is less because you have more surface area supporting your weight. Skates have significantly higher pressures because the same weight is supported by much less surface area. Pressure increases the heat and is well known to melt ice in certain situations. If you've ever tried to skate in Winnipeg on a cold winter's day, you would know it's not possible if it's too cold. You might want to get your physics right.

ZapperZ said...

You, sir, needs to have your physics updated by reading that Physics Today article.

Zz.

Tapsa said...

Hi! In my undergraduate Statistical Physics class it's a standard homework problem to show by direct calculation, that pressure-induced melting does *not* explain skating on ice :).
http://www.facebook.com/CourseOnStatisticalPhysicsAtAaltoUniversity