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Re: heat is still a noun



At 05:04 PM 5/7/01 -0700, Larry Woolf quoted Craig Bohren as saying in part:
What is this vague stuff called "thermal energy"? Why not just say internal
energy or just energy? As far as I have been able to determine there are
only two kinds of (non-relativistic) energy: kinetic (energy of motion) and
potential (energy of position). Thermodynamic internal energy (internal
energy or energy for short) is the sum of these two kinds. So why do we need
a term "thermal energy"?

Being unable to recognize the distinction between thermal energy and other
forms of energy indicates a non-understanding of basic thermodynamics.

To illustrate the correct distinction:
1) Start with a large metal spring. By carefully selecting the
materials, and using other techniques familiar to watchmakers, arrange that
the force of the spring is independent of temperature to a high degree of
approximation. Store a lot of energy in the spring. Use the spring to
drive an electric generator. Use the generator to drive an electric
motor. Use the motor to impart energy to a second spring.

This nonthermal conversion process can be carried out with very great
efficiency. The efficiency is independent of temperature, to an excellent
approximation, over a wide range.

2) Start with the same spring, with the same stored energy. Convert the
stored energy to thermal form, by letting the spring unwind against a
brake. No energy has been lost; it has just been transformed. Use the
energy in the brake to drive a heat-engine. Use the heat-engine to
compress a second spring.

This thermal conversion process cannot be carried out with very great
efficiency. The efficiency is limited by the temperature of the
brake-material relative to the temperature of the surroundings, whereas no
corresponding limitation applies to the nonthermal conversion described
previously.

==============================

I like this discussion, because it affords an opportunity to clear up some
basic misunderstandings. (This is a big improvement over certain other
discussions, where the argument against using "heat" as a noun was based on
little more than word-games and name-calling.)