OT: speed skating

[cth95]

One more thing I thought of while watching ski racing yesterday.  A longer ski will have a longer turning radius than a shorter ski with a similar sidecut.  If you compare the slalom skis that go up to the racers' noses, and watch the quick turns they are able to make, you will see what I mean.  A ski with less sidecut (straighter) will also have a longer turning radius.  This is ok in moguls, because the skiers are making short turns by skidding the skis back and forth between the moguls.  In slalom racing, the skiers carve short-radius turns by using the shape of the ski.  If you look at tapes from before the advent of the shaped skis, the slalom racers had to essentially step from gate to gate to get into the next turn quickly enough. Now the shape of the ski allows them to simply crank the turn within a small enough radius.  Bode Miller was the first to really figure this out, and it allowed his career to take off.

[canuck89]

haha.  The point seems to need explaining every few posts in this thread.  I agree with you.  Just refer people to the top from now on.  :-D

[canuck89]

This is the exact concept on which skates work.  I do not know if it occurs on skis, due to the whole issue of lbs/inch that you mentioned.  On skates though, the thin (and short) blade creates so much pressure that the ice indeed does melt and allows minimal friction (at least less than "skating" on ice itself).

[cth95]

Skis slide on a momentarily melted surface as well, but I don't understand physics well enough to know how length and width of the ski affect the force of friction.

[jtwcornell91]

[quote canuck89]This is the exact concept on which skates work.  I do not know if it occurs on skis, due to the whole issue of lbs/inch that you mentioned.  On skates though, the thin (and short) blade creates so much pressure that the ice indeed does melt and allows minimal friction (at least less than "skating" on ice itself).[/quote]

Actually, if you do the math, this is not true.  You just need to apply too much pressure to lower the melting point of the ice significantly.

[canuck89]

Sorry, i thought it was a given that the pressure was indicative of increased normal force per unit area.  This force then leads to more friction, then heat, then melted ice.  You are correct about pressure lowering the melting point.  :-P

[David Harding]

[quote canuck89]This is the exact concept on which skates work.  I do not know if it occurs on skis, due to the whole issue of lbs/inch that you mentioned.  On skates though, the thin (and short) blade creates so much pressure that the ice indeed does melt and allows minimal friction (at least less than "skating" on ice itself).[/quote]Here's an explanation of the current understanding of how ice skates slide. http://www.exploratorium.edu/hockey/ice2.html It's NOT melting the ice with the pressure, though that idea has long been taught.  This page is just one in a whole site devoted to the physics of ice hockey.  http://www.exploratorium.edu/hockey/  I highly recommend it.

[canuck89]

more reputable than any of us at least.  :-}

[Pete Godenschwager]

Here's another article about why ice is slippery for those interested:

http://www.nytimes.com/2006/02/21/science/21ice.html?hp&ex=1140584400&en=b7887df660077ce0&ei=5094&partner=homepage