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Re: What Flows?



I offer these quotes from what I think IS the best selling College textbook
just to prove to myself that we who are comfortable with this nomenclature
aren't complete idiots. We may be 'wrong', but at least we're in good
company--(at least very RICH company)! ;-) (-;

If that is your arbiter of taste, that's fine. We stopped using Serway and
Faughn three years ago, and so far as I know their definition of "thermal
energy" is not accepted anywhere in respectable peer reviewed journals.

It seems to me that "thermal energy" must be connected somehow to heat.
To illustrate the problems with this arbitrary partition of energy let me
propose some questions and ask some more questions about the questions.

1. Take a quantity of gas in an insulated cylinder and allow it to expand
a factor of two. It will cool off, of course. By how much has its thermal
energy changed in this process?

2. Now heat the gas until it returns to its original temperature. By how
much has its thermal energy changed in this process?

3. Finally, with the gas in contact with a reservoir at the same
temperature, compress it by a factor of two. The gas will have returned
to its initial state. By how much has the thermal energy changed in
this process?

Process 1 is adiabatic. No heating is done. Does the change in thermal
energy relate in any way to heating? Why is thermal energy a useful
concept in this case?

Process 2 is isochoric. Heating is the only process occurring.
Presumably *all* of this energy goes into the thermal category, agreed?

Process 3 is isothermal, and (negative) heating of the gas occurs. The
temperature of the gas does not change, and if the gas is ideal neither
does its internal energy. If you say its thermal energy does not change
when it is heated, why is thermal energy a useful concept in this case?

Finally, for the whole cyclic process there has been a net heating done
by the system on its environment and the system has returned to its
initial state. Thus the amount of "heat energy" that can be generated
by cycling this device is unlimited, and since the system is unchanged,
it has the same thermal energy at the end of a cycle as it had at the
beginning. Looks like a free lunch - heat with no loss of thermal energy.

I can go through these processes with canonical language and make them
perfectly understandable.