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Re: ENERGY WITH Q



MORE ON MODEL 2

The kinetic theory of gasses provides us with the first
glimpse of the true nature of caloric. It shows that for a
simple case of an ideal gas (mono-atomic molecules)
Q can be calculated as 1.5*N*R*T, where N is the
number of moles, R is the universal gas constant and
T is the absolute temperature. In the first physics course
this is usually generalized by saying that the amount of
thermal energy present in any object is directly
proportional to its absolute temperature.

The kinetic theory of gasses is a gigantic step toward
the understanding of the true nature of heat. But this
should not prevent me from associating this theory with
the Model 2. It is the central theoretical part of that model.
Solid substances can be viewed as molecules connected
with springs; the true nature of springs can be announced
but not explained until electric forces are discussed. The
amount of thermal energy contained in a solid is determined
by random motions of interacting molecules about their
equilibrium positions. The term "random molecular energy"
can be used but, in my opinion, it is not needed. Thermal
energy is the same thing as random molecular energy; it is
partially kinetic and partially potential. Is this acceptable?

Likewise a distinction between the "sub-microscopic" and
"macroscopic" energies is useful but not essential. The
term "internal energy" was often debated on this list. I do
not remember who said what but the opinion I formed was
that the internal energy can be both macroscopic and sub-
microscopic. To illustrate this I would refer to a mechanism
with spinning wheels (at a non-zero T). Is this acceptable?
Ludwik Kowalski
P.S. *********
In a private message XXX suggested that the "energy
without work" approach is desirable. As you recall,
the thread ENERGY BEFORE Q started as an attempt
to introduce energy without work. I gave up because
I recognized that this approach is conceptually more
difficult to introduce than the traditional approach. For
example, how do we argue for the PEspr=0.5*k*x^2
or for the PEcap=0.5*C*V^2, etc.

In the message posted last night the word "heat" was
associated with "caloric" for purely historical reason.
If caloric is not a substance then it is something else.
The name "heat" was probably chosen to recognize "it
is not a material substance" idea. The word "heat" was
also associated with thermal energy (as many did on this
list before me). It is important to emphasize that, unlike
work, heat is a form of energy. Work is a concept
used to introduce different forms of potential energy.

In my opinion the term "total energy of a system" should
be used for the sum of all forms of energy, including those
which have not yet been recognized by physicists. That
is why E was not called energy. In Model 1 E was called
"mechanical energy" while in Model 2 it was called
mhenergy (mechanical plus heat). It is easy to invent new
words, it is difficult to impose them on teachers. Suppose
we agree that some new words would help us to avoid
misconceptions. Can we then ask our establishment,
AAPT, to promote them officially? What is impossible
for an individual may become possible for an organization.

It is remarkable that a very primitive model of thermal
energy (caloric = fluid) was used successfully to promote
science and technology. The operational definition of the
unit of heat, calorie, remains valid no matter what we
think about the "true nature" of heat. I think that a section
on the mechanical equivalent of heat is extremely valuable
in the first physics course.