Re: [Phys-l] physics of dissipation

[John Denker <jsd@av8n.com>]

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

> The sound is intense enuf to produce defects?

Sometimes.

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.