Why is ice slippery?

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Interesting NYT article about the question of why ice is slippery. It appears that the standard answer to this question (the pressure lowers the melting point) is wrong. The change in the pressure only lowers the MP about .03 F, and ice is slippery at well below 32 F. The two best competing answers seem to be:
  1. Friction from your skate blade or shoe causes the ice to melt which makes it slippery. This seems to be true but incomplete. The problem here is that ice is slippery even if you're standing still.
  2. Ice has an intrinsic liquid layer on the outside. It's not clear to me exactly how the physics of this works (but then what do you expect from something you read in the papers), and atomic force microscopy testing doesn't seem to indicate that the surface of ice is slippery at the microscale, which suggests that the liquid layer isn't a complete explanation.

Sort of amazing that such an apparently simple phenomenon still isn't understood.

UPDATE: Corrected the temperature measurements to be F instead of C. Thanks to Paul Hoffman for pointing this out.

4 Comments

It is interesting that you don't take the same combative stance with the Ice Slipperagists that you do with the Intelligent Designers: "If we don't know how, it must not be."

Ice is quite slippery at 32C. In fact, it's a tepid liquid.

"Corrected" measurements to °F? and exactly why do you assume that °F is correct and °C is not?

Because as Paul points out water freezes at 0 C, so at 32 C, it's it ice.

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