Re: coefficient of friction

[Joseph Bellina <jbellina@saintmarys.edu>]

This is a very complex topic having to do with the details of the facing 
materials.  For example, if the speed is high enough to melt one side of 
the interface, the coefficient goes down.  The field of tribology is 
really not very old, and there is little fundamental understanding of 
what happens at a microscopic level.  I believe the usual data seen in 
textbooks are for dry steel rubbing on dry steel...polished as well.
To give you another example of how touchy friction is, if the interface 
is metal on diamond, about one half an atomic layer of hydrogen adsorbed 
on the surface of the diamond will change the friction force by a factor 
of more than two.
Most of the time we are rubbing grease and dirt on grease and dirt, since 
most materials are covered with several atom layers (at least) of the 
gunk.
Sorry I can't provide a simpler answer.

cheers

On Tue, 8 Apr 1997, Michael Crofton 
wrote:

> I know that in general physics we regard the coefficient of kinetic
> friction to be constant no matter what the speed of the sliding object. 
> I have read that in "real life", the coefficient increases at high
> speeds.  Why does this occur, and what is considered "high speed"?  Is
> there a good source on the topic?
>
> Thank you,
>
> Michael Crofton