# Coefficients of Friction & Restitution v Some Generalized "Contact" Coefficient

Doesn't friction ultimately involve impact on some microscopic scale?
And doesn't impact ultimately involve friction on some microscopic
scale?
Both can lose as much energy to heat as to kinetic energy.
Both vary from 0 to 1.
Is there _really_ any useful fundamental difference?
Bret Cahill
I would suspect that friction has a lot to do with the interference of surface irregularities as one surface slides past another. Still, even if we had two perfectly smooth surfaces, down to the atomic level, would there still be friction? I suspect there would be. I also suspect that there has been a lot of work done on this question.
By the way, is there any reason why a friction coefficient can't be greater than one?
Olin Perry Norton
Dear Olin Perry Norton:
"Olin Perry Norton" wrote in message news:gm53rc\$ais\$ snipped-for-privacy@nntp.msstate.edu... ...
No, simple examples are glued surfaces and velcro.
David A. Smith
One is equal to the weight so the two surfaces would never touch.
They don't count.
Bret Cahill
That doesn't make it fundamentally different than impact at the atomic or molecular level.
You'ld be surprised at the amount of work that _hasn't_ been done on a _lot_ of really basic questions.
I recently read some book on rheology that concluded: And if you're wondering why this chapter is so short it's because no one has done any work on it.
There's no job or at least no work shortage for engineers.
It's still the wild west.
Bret Cahill
No - racing tires regularly exceed 1.0 in racing use
Brian W
Melted rubber does not count either.
Bret Cahill
It doesn't take melted rubber to exceed 1.0
Brian W
Bret Cahill wrote, On 2/1/2009 8:01 PM:
Mr Cahill, You seem to be fond of making blanket statements that whole subject areas in engineering are being ignored (an implying that you are the one who holds the secret answers to these difficult problems). Let me assure you that hundreds of scientists and engineers are working to try and understand the causes of friction and how to mitigate its effects. See:
Brat: Another set of half-smart brain-farts from Cahill. The only REALLY interesting cases are where the coefficient is outside of the 0 to 1 range (adhesion, galling, etc.) When simple definitions get violated you might actually learn something.
Pittsburgh Pete
Why not just chain a piece of ice to a warm teflon fry pan and claim the coefficient is greater than one?
Bret Cahill

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