Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Work and Energy and Thermo



But IMHO an even bolder step is needed to
achieve the goal of simplicity, clarity, and correctness ... namely walking
away from the W+Q equation entirely.

I have been thinking about John's suggestion -- He may be right!

The problem, however, is imbedded quite rigidly in our discipline's adamant
reification of "energy" and "heat" and the "flow" there of. We end up
wanting Q to be associated with a temperature difference and to flow
into/outof a system; this is coupled with the penchant to have energy flow
as well -- with the additional strange thinking that Q is energy.

The difficulty began a long time ago = even before Aristotle = and we just
can't get rid of it. We ignored Rumford -- maybe because he was a traitor
in some eyes. Another rigid difficulty was Carnot's fetish (an arms
development consideration -- as is much of science) with the steam engine
which led to the ubiquitous adiabatic cylinder with a
piston. Thermodynamics was born in this grotesque simplification.

Young _invented_ the idea of the property of "energy". Kelvin and Clausius
invented the idea of "entropy". Then came the First Law. But out of sheer
momentum Q had to do with hot things. Then the gang figured out that
DS=IntQ/T sort of.

But this equation had to do with the warped views of Q and was valid for
only the very narrow case of an adiabatic cylinder/piston which
was operated reversibly.

Not real systems.

The reality is that Q _and_ W are _both_ work and the First Law is no more
than the W/E principle. Maybe it is because of mental momentum we quickly
say then that Q is microscopic work, done by colliding molecules, and W is
macroscopic work -- and that Q has to do with hot things.

Actually Q is _any_ work (or the fraction of the total work) which changes
the entropy and W is work which does not.

Now John seems to agree with this result -- He gets there by a tortured
path, but he gets there.

The fact is that any attempt to distinguish between Q&W is futile -- except
for the very narrow example of Carnot's simplified steam engine piston --
where, maybe by happenstance, W does not change the entropy and Q does. I
would be delighted if someone could provide additional examples -- I have
been looking for years.

Thus, I am persuaded to agree with John that, except for this narrow case,
the First law is worthless.

Now, Joel, we are back to the point where you and I left this
reoccurring/continuing discussion a few years ago.

Jim

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