Naked Science Forum

General Science => General Science => Topic started by: Geezer on 28/11/2010 18:54:06

Title: Why do skis slide on snow?
Post by: Geezer on 28/11/2010 18:54:06
I believe there was a lengthy thread on the subject of how ice skates work, but I'm not sure if skis operate for the same, or somewhat different reasons. Certainly, the pressure exerted between the surface of a ski and snow is a lot less than the pressure exerted by an ice skate on ice.

Also, skis are usually waxed, and the characteristics of the wax can make quite a difference, depending on temperature.

Any clues?

UPDATE: BTW, this came to mind because of the amount of snow we've had here. So far, it's about sixteen inches, and it's not even December yet. Last year, we didn't even get sixteen inches during the entire winter!
Title: Why do skis slide on snow?
Post by: maffsolo on 28/11/2010 20:27:48
Skiing over snow is a combination of both wet friction and dry friction: too much water will create "wet drag" (suction), while too little water will result in "dry drag" (friction). A properly selected glide wax will aid in this delicate balance.
Title: Why do skis slide on snow?
Post by: Geezer on 30/11/2010 07:20:03
In one of the Richard Feynman interviews on Youtube, he seems to suggest that the effect on ice might be related to the fact that water expands when it freezes. Was he speculating, or was he on to something?
Title: Why do skis slide on snow?
Post by: jartza on 30/11/2010 07:37:23
Feynman means melting & compression is related to freezing & expansion
Title: Why do skis slide on snow?
Post by: Geezer on 30/11/2010 07:45:29
Quote from: jartza on 30/11/2010 07:37:23
Feynman means melting & compression is related to freezing & expansion

Quite possibly. How does that effect the phenomenon?
Title: Why do skis slide on snow?
Post by: jartza on 30/11/2010 08:00:35
When you force ice to water's density the ice turns into water.
Title: Why do skis slide on snow?
Post by: Geezer on 30/11/2010 08:38:45
Quote from: jartza on 30/11/2010 08:00:35
When you force ice to water's density the ice turns into water.


Is that what skis do? I don't think they exert a great pressure.
Title: Why do skis slide on snow?
Post by: jartza on 30/11/2010 09:08:12

I'm not knowledgeable about skis. I just had to tell what R Feynman was thinking.