Re: CONSERVATION OF ENERGY

[brian whatcott <inet@intellisys.net>]

At 10:56 7/16/97 -0800, John Malinckrodt wrote:
> I'd like to suggest that much of the confusion here is the result 
> of a failure to appreciate that 
>
>          kinetic friction is not a heating process.
>
> I think this common confusion has to do with the fact that both 
> may be considered to involve distributed, microscopic works done 
> at the interface between two systems....

> Note also that heating can be done reversibly while kinetic 
> friction is always irreversible.  This is why, in order to 
> determine the temperature rise that accompanies kinetic friction, 
> we often construct an *alternate* path between initial and final 
> states that involves a heating process with an "equivalent" heat 
> transfer. ...
> A. John Mallinckrodt 

John offered here a calm coherent explanation of why a particular 
construction of thermodynamics ( perhaps I should say the 'correct' 
or at least 'orthodox' construction ) needs me to carefully distinguish
between 'heating' and 'raising the temperature' which is also known as 
'warming' or any number of other synonyms.
 
 He offers in support that friction is irreversible but heating may be
 reversed.

I need first to offer thanks for this contribution; it is clearly
aimed 'on the level' ( a feature I have previously noted in a didactic
contribution of Bowman's ) but that is just a personal preference.

 (I am acutely aware that the teachers who can summon passion in their 
cause are more likely to leave a long-term trace of their efforts 
than the sad vestiges which researchers are too apt to report as the 
after-effect of many fine teaching efforts.)

But I digress.
 John talks of friction as though it somehow embodies the deepest 
principles of thermodynamics and bears even on quantum mechanics.

 The sad fact of the matter is that kinetic ( or dynamic) friction is 
one of the poorer models that are in the physical armamentarium.
 Friction force is not constant with speed, nor with contact surface 
area but we suffer the variability as a necessary simplification 
in this physical model.
 It is not alone - one could mention the perfect gas law, of which 
there are at least three elaborations, all of which break down near 
a change of state especially.
 

 Recent research corroborates the view that at the microscopic level,
friction force is a linear function of contact area.
  We are led to believe that this apparent area-independence is at least
partly the result of a surface bearing on only three or four contact 
patches, no matter what the apparent area may be.

  John describes the detail of energy conversion to work as the
elastic deflection of asperities, or their progressive shearing.
  Indeed, it is evident that this model of friction is quite consistent 
with a 'work' process.

And so I come to the crux of my thermodynamic counter-argument:
 one reason for confusion in this area is that teachers associate only 
'friction force' with work as opposed to its being a 'heating process'; 
I can now assert that -

 If there is any retarding force whatsoever which serves to 
dissipate kinetic energy - then that is by definition 'work' no matter
what the modality and no matter HOW faulty the 'friction' model.

[Epilog]
If there is a kind soul who has persisted in my essay to the end, 
I would like to ask for a copy of the article to which John refers -
Sherwood & Bernard, AJP
I am happy to pay the copying and postage costs, and assure any
prospective saint that this is a permissible use of copyright material.

Sincerely,
brian whatcott
1041 E Liveoak
Altus OK 73521
brian whatcott <inet@intellisys.net>
Altus OK