## Wednesday, January 13, 2016

### The Mysteries of Ice Skating

That the physics of ice skating are still is not fully understood is not surprising. Making measurements on a small area that has dynamic pressure conditions wedged between the ice and the steel blade is extremely challenging. We know that ice is inherently not slippery, and that only because of the pressure of the blades somehow "melting" the ice or otherwise creating a liquid-like surface that skating happens at all. Long ago as an undergrad, I was taught that the pressure of the blade alone is enough to alter the melting point of the ice. This change can be calculated via the Clausius-Clapyeron equation but a quick back-of-the-envelope estimation shows that an enormous amount of pressure is needed. This was handwaved away by the instructor stating that skates are hollow ground (i.e., they are concave down as you look to the length of them) to increase the pressure.

Imagine my shock a few years later when I took up speedskating and found out those blades are flat ground. That right, the skates that are the fastest are the ones with the largest contact area. So much for Misters Clausius and Clapyeron (and my instructor).

New research offers a potential new explanation of ice skating. It's currently pay-per-view so I haven't read it (it will likely become downloadable in the near future as are most of the PI's papers, but I wonder if the article will really get at the dilemma that I mentioned above: the role of contact area.

Hollow ground skates are used for sports where turning tight corners is necessary, so have a "biting" edge is essential. In speedskating, having a friction free glide is essential to maintaining speed. But are there points where either approach becomes too extreme? Can skates with an extremely small contact area (an atomically thin edge?) have any value or would the performance degrade? And for speedskates, would a larger surface area aid or hinder performance? Is there a limit on either end?

I've puzzled on these questions over the years, but the greatest mystery to me is this: is there any value in creating a hybrid skate? One that is hollow ground on one or more portions and flat ground elsewhere. Maybe hollow on the front and back for turning on the toes or heels, but flat ground in the middle for maintaining speed. Even without understanding the physics of ice skating, I would love to see someone try such hybrids as I think it could provide in some very unusual results.