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Re: [curt] best temp for friction:
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villageidiot
Dec 10, 2009, 4:40 PM
Views: 10594
Registered: May 12, 2005
Posts: 104
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curt wrote: You're not looking at it correctly. If you start with climbing shoe rubber at zero degrees F (for example) and begin increasing the temperature, the coefficient of friction will indeed go up. But, for each rubber, there is some temperature at which the coefficient of friction peaks--and then decreases with a further increase in temperature. By the way, this is actually because the rubber is getting softer. After a point, softening of the rubber no longer enhances the ability of the shoe rubber to "stick" to the rock--it actually does exactly the opposite. Curt
From statistical mechanics you can derive a relationship showing that th elastic modulus of a crosslinked network, like that found in show rubber, is proportional to the temperature. Meaning that the elastic modulus increases with temperature. While I am not sure exactly what you mean by "softer" I doubt that climbing shoe rubber actually gets softer at higher temperatures.
I am also pretty suspicious of you first claim that there is a maximum of the friction coefficient with respect to temperature. In "Viscoelastic Properties of Polymers" there is a master curve for the friction coefficient versus velocity. This curve was formed by time-temperature superpositioning according to the WLF equation. I believe this would imply that the friction coeffiecnt incerease monomtonically in a rubber.
Edited:
Your description is consistent with the material undergoing a glass transition. I just find it unlikely that many climbers climb in temperatures were that type of behavior is relevant. I was climbing in 35F a couple weeks ago and the soles of my shoes still did not seem glassy.
(This post was edited by villageidiot on Dec 10, 2009, 5:22 PM)
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Edit Log:
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Post edited by villageidiot
() on Dec 10, 2009, 5:22 PM
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