Re: ENERGY WITH Q, STEP 2.

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

Ludwik Kowalski wrote:

> 8) What is next? Another fighting about words? I hope
> not. How to approach the first law of thermodynamics
> without imposing it? Is it OK to say, for the time being,
> that from now on it should be KE+PEgrv+PEspr+Q
> that remains constant? Be patient Jim. So far the above
> statement is an old generalization of experimental facts
> established by Joule and others. Q stands for the
> appearing amount of caloric, a pseudo-fluid, we can
> say.

9) Why was work, a physical quantity expressed in J, was not
made part of the above sum? Because work is not energy, it is
a number showing how much energy was transformed from
one form to another. In free fall, for example, KE increases
while PEgrv decreases and work (weight*distance traveled) is
a measure of this energy transformation. Adding work to the
above sum would be like counting something twice.

10) In other words, work is not like Q. If we ignore Q then the
sum which was constant in an idealized world would no longer
be constant in a little more realistic world. Thus it is OK to say
that caloric is a form of energy while work is not a form of
energy. Since in common language the word heat is often
confused with temperature we will introduce a new word for Q,
we will call it thermal energy. E=KE+PEgrv+PEspr+TE=const.
This relation, experimentally established by Joules, was an
important first step toward better understanding of our world.
We say that energy E is conserved when work is done by
various forces.

11) For some forces, such as air resistance or friction, work
is always associated with generation of caloric. For other
forces (from weight or springs) work does not result in
generation of caloric. We say that forces whose work does
not generate caloric are conservative while forces whose
work does not generate caloric are nonconservative. These
terms (conservative and not conservative) were probably
were introduced before heat was recognized to be a form
of energy.

Personally I would say that forces are either heat producing
(non-conservative) or heat producing, like friction. Heat
producing forces are usually called dissipative because
generation of caloric is always associated with the decease
of KE+PEgrv+PEspr. The sum of these three terms is
usually called "mechanical energy" while the above sum
of four terms is called "total energy." In reality total energy
is not limited to four terms; we will learn about other forms
of energy later. AT THIS STAGE (BUT NOT EARLIER)
I WOULD QUOTE THE SUGAR CUBES STORY OF
FEYNMAN.

11) What is next? Work at the expense of TE, I suppose.
Please help me; I am running out of steam. Here is the
summary of the proposed sequence:

      0) Calorimetry, kinematics and Newton's laws.
>   1) Kinetic Energy
>   2) Gravitational potential energy
>   3) Work
>   4) Potential energy in springs.
      5) Caloric=TE
      6) Work to increase TE
7) Engines to decrease TE

It would probably be wise to eliminate inappropriate
formulations in "chapters 0 to 6" before attacking item 7.
We must agrre, at least temporarily, on terminology.
Otherwise it will again be a battle about words not
concepts.

In particular:
a) What is wrong with E=KE+PEgrv+PEspr+TE=const.?
b) What is wrong with CALORIC=HEAT=TE?
c) What is wrong with not emphasizing the "path
    independence" in the definition of conservative forces?

By looking at the item b I anticipate a question about the
latent heat, or about nuclear energy. These are terms
which are deliberately ignored. It is impossible to deal
with everything at once. [One can say that missing
parts are hidden on the right side of the equation.]
Ludwik Kowalski