h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When it's frozen into snow, as well as building snowmen with it, and throwing it at people for fun, you can also ski or toboggan on it. When it's frozen into solid ice, you can skate on it, as it can be *very* slippery.
Recent research indicated that the slipperyness isn't simply a matter of ice melting under the pressure of skates, nor is it down to melting due to friction. Apparently, even at temperatures significantly below the freezing point, there can be a terribly thin surface film of liquid water on the outside of ice crystals, (something to do with surface tension, I think) and this contributes to the lack of friction.

My 'O'-Level Physics book tells me that the thin film of water that makes ice slippery is caused by the 'work done against friction'.

Any the wiser? Nor me.

Friction was one possible cause that the recent work didn't seem to think was much of an explanation. I think the way they put it was, very roughly : If you're standing still on skates, there isn't any *sliding* friction to generate heat, (and *static* friction can't generate any heat) but it's still pretty slippery.

It may make a small contribution, but it's probably not the main reason. I'll try and dig out the article (though since I've just moved, it's undoubtedly buried at the bottom of a crate of books or papers somewhere.)

Unfortunately, O-level science books sometimes give explanations for phenomena that vary from not-quite-right through oversimplified to just-plain-wrong.

Very true.

A-level textbooks are better, but one of mine still claims that medieval windows are thicker at the bottom because glass flows very very slowly downwards, when in fact the real reason is that they were made unevenly and put in that way up so they wouldn't fall out.

Nice article, by the way .

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