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Re: [Phys-l] physics of dissipation

On 01/14/2010 12:54 PM, Bernard Cleyet wrote:

The sound is intense enuf to produce defects?


1) I was using "sound" as an informal synonym for
internal motion. Sound modes are a basis set for
describing almost any type of distortion. Whether
you want to continue this viewpoint past the point
where we get actual cavitation is partly a question
of taste and is at best highly technical. I don't
want to get that technical. Like I said, understanding
the microscopics of frictional sliding is hard,
and I don't have the time or motivation to dig too
deeply into it right now.

2) We know that sound can produce cavitation, as
in sonoluminescence. It can break chemical bonds
and even break nuclear bonds, as in Seth Putterman's
Mr. Fusion machine.

3) Sound or no sound, we know that friction can
break bonds. Scrape a steel rod against a brick.
It is macroscopically obvious that both the steel
and the brick get ripped apart.

On the other hand, virtually all of the heat capacity
of an ordinary solid is in the phonons. The heat
capacity due to creation and/or motion of crystal
defects is tiny ... so tiny as to be unobservable
except rather close to the melting point.

I thought the increase in S was due to the distortion of the metal
(breaking of bonds and atom movement) at and near the contact
surfaces. Sound is the means of diffusion of the local increase in
atomic motion?

Again, I am not in the mood to distinguish "distortion"
from "sound".

Simply breaking a bond (as in cleaving a crystal) is
neither friction nor heat.

Again: at ordinary temperatures (not too hot and not
too cold), most of the heat capacity is associated with
the phonons. If you want to understand heat, at some
point you're going to have to couple to the phonons.