Tuesday, February 21, 2006
Explaining Ice: The Answers Are Slippery
This is a really nice piece of science writing from today's New York Times. (Registration required, I think.) It turns out there’s a lot we don’t know about ice, of all things. Like why it is slippery.
The explanation I remember from high school physics or some other dim and distant time, is that ice skating works because the pressure of the blade melts a minute layer of ice, making it slippery. Not so, it seems.
According to calculations, in the best case the pressure from an average ice skate blade would only lower the melting point by .03 degrees F, hardly enough to make any difference. And it doesn’t explain why ice is still slippery to a person standing on it in regular shoes, where the weight is dispersed over a much larger surface area of shoe sole, vastly diminishing the melting effect.
Now, this calculation didn’t require high powered electron microscopes and delicate lasers to figure out. The physics and math necessary to figure out that the “skate pressure melts ice” theory is bogus has been around for years. So why did we get handed the same line of hokum for all this time?
Perhaps because there isn’t any convincingly better explanation, although the Times article does advance a theory from a Berkeley surface chemist that a minute layer of the surface of ice is actually liquid at all time. Our uncertainty is really odd, ice being such a common material and the cause of so many problems. “Why is ice slippery?” may not be the kind of question that gets much funding, although you’d think that the secrets of friction reduction would be, so to speak, a hot topic.
The explanation I remember from high school physics or some other dim and distant time, is that ice skating works because the pressure of the blade melts a minute layer of ice, making it slippery. Not so, it seems.
According to calculations, in the best case the pressure from an average ice skate blade would only lower the melting point by .03 degrees F, hardly enough to make any difference. And it doesn’t explain why ice is still slippery to a person standing on it in regular shoes, where the weight is dispersed over a much larger surface area of shoe sole, vastly diminishing the melting effect.
Now, this calculation didn’t require high powered electron microscopes and delicate lasers to figure out. The physics and math necessary to figure out that the “skate pressure melts ice” theory is bogus has been around for years. So why did we get handed the same line of hokum for all this time?
Perhaps because there isn’t any convincingly better explanation, although the Times article does advance a theory from a Berkeley surface chemist that a minute layer of the surface of ice is actually liquid at all time. Our uncertainty is really odd, ice being such a common material and the cause of so many problems. “Why is ice slippery?” may not be the kind of question that gets much funding, although you’d think that the secrets of friction reduction would be, so to speak, a hot topic.
