Re: ENERGY WITH Q

[Jim Green <JMGreen@SISNA.COM>]

> >Both Q and W are _work_!
>
> This is highly unconventional. Being unconventional doesn't make it wrong,
> but it calls for detailed explanation.

Yes, John, unconventional -- because of the unhelpful legacy of Carnot et
al.  John we have gone over this many times in the recent and past years --
so many times that I find myself embarrassed saying it yet once again --
Folks, just look at my web page!!!!!  There is an error there but and the
page is quite unfinished but you will get the point of Q is work!!!  This
is not a "new convention" it is TRUE.  See below.

> We are being given the new notions of W and Q. This raises many questions:
>   -- If W is work and Q is work, then W is not the total work. What symbol
> shall we use to represent the total work?

I don't know that you need a symbol for Total Work -- where would it be
used?  But if you want one, you get to choose!!!  Lets us call it D for
Denker.  I agree  that W is an unfortunate choice, but we seem  to be stuck
with it.  W is the work done which does not change the entropy.  Q is the
work which does. ie deltaS=Q/T.  We both agree that this is not very
helpful except in the very narrow case of the adiabatic cylinder with a
piston. But, as I have said many times, this doctrine is due only to the
steam engine  (which BTW Carnot thought of as a war machine)

It just so happens that the reversible work done by the piston  does not
change S -- just a quirk!  Not all macroscopic mechanical work follows this
rule -- thus The First Law is not really much help -- and thermodynamics
(as opposed to thermal statistical physics) fails in most real cases.

>   -- How are W and Q related to "work" in the sense of F dot ds?

Not always, but in the intro course Q is done by high speed molecules
colliding with low speed molecules -- the molecules of a hot plate
colliding with the molecules of a glass beaker -- the molecules of a
propane torch colliding with whatever.

During the collision Work is Done!!!

>   -- Does F dot ds equal W?

Yes -- well in some F dot ds's the result is "W" -- in some cases the
result is "Q" -- I restrain myself from foul four letter words.

>   -- Does F dot ds equal total work?

Yes -- if the total F dot ds is considered

>   -- Does the total work equal W plus Q, or are there other contributions?

This is a philosophical question: I reviewed a paper once where the author
invented a new thermo state function with some curious bells and whistles
-- there could be a class of work which changed this new function only --
in which  case  there  would be something like

deltaE = W + Q + L

The paper was not published.

> I'm mystified. Without a great deal of additional info, I cannot imagine
> how the notion
> >        Both Q and W are _work_!
> is helpful to anyone.

Well, John, for starters such a view would be correct for a change. <g>

And BTW students understand this view much more easily -- after cartoon
physics and Bill Nye are dealt with

Jim

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen