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]

Re: PHYS-L digest 507 Two meanings for the word heat and more.



The internal energy does not change when
friction
slows
down a brick sliding along a horizontal surface. But a conversion of
kinetic
energy into thermal energy does take place in the system.
Ludwik
Kowalsk
*********************************************************************
I now believe that Ludwik includes the initial kinetic energy of the
brick in the internal energy, U, a term in the statement of the First
Law. OK, that's what I would do, too; but would you include the
potential energy associated with the fact that System A, all of which
'weighs' 100 kg (it is closed to transfer of mass none of which is
converted to energy) is 15 meters above the lab floor, suspended from a
rope and pulley arrangement, which might as well be frictionless just to
CMA (by analogy with CYA) in case I wish to make some calculations later.


During the course of a sequence of experiments System A will exchange
energy and otherwise interact with System B and System C, which are
resting on the lab floor. Are you going to add the relative advantage in
gravitational potential energy to the internal energy of System A? If
not, where are you going to take credit for it, which you had better do,
as it will be "cashed in" subsequently. Now, can I find out who didn't
like this idea without scanning all my e-mail? Will any drawbacks to
adding it to U arise? What about dealing subsequently with a System C
whose gravitational potential energy is known relative to some other lab
and the relation between the labs cannot be found? Is that a no deal
situation? "We at Cavendish do not interact with systems the bases of
whose quantifications are not accompanied by all appropriate
transformations to Cavendish data. So there. And, we dress for dinner!"
Before I remove the gravitational P.E. term from the U of my system, I
would like to see what you sharps say.

Now, I wish to make two sensible observations - with apologies to
Leigh for the first and to no one for the second.

First. The expression thermal energy is employed by nearly every author
in my battalion of authors on thermophysics, including Feynman in his
Lectures, which I am reading. (Which is larger a battalion or a
division?)

[Off-topic pleasantry. By the way, the writers of Feynman's lectures in
consort had a less well developed sense of humor than did Feynman. When
I started I read the section on planetary motion, the film corresponding
to which I saw years ago at Courant. "The ancients believed that the
planets moved around the sun because angels pushed them in the directions
of (the tangents to?) their orbital trajectories. We now know that is
false. The angels push from the sides." The writers blew that joke
totally. In the movie, it brought the house down.]

Also, Feynman gives the distinct impression that he is taking energy to
be the capacity to do work - even though he specifically states that no
one knows what it is. This is very plain. I shall use Feynman again,
perhaps improperly, but he can handle the moral weight. Someone,
anyway, said that after he explains that heat is the transfer of thermal
energy across the control surface, he next says that no way will he stand
still for all that locution and from now on when he refers to the "heat
in" and the "heat out", you damn well better know what he means. I
believe we all might have trouble referring to"heat in" in fewer words
than that if we get linguistically rigorous.

Now, does anyone - other than Ludwik - remember my initial step in the
process of defining understanding when I attempted to define only a true
statement, which seemed like a promising first step. That was a
completely unambiguous statement that was virtually impossible to
misunderstand. The only thing that could go wrong is you the readers
might get frustrated, bored, or might make insufficient effort to
memorize all of the machinery that had to be defined and set up and have
its operation explained all before anyone forgot the first sentence. The
difficulty is almost the same as any of us might experience trying to
read the *Critique of Pure Reason* without a special Kantian dictionary
and a pony of some sort. We keep forgetting stuff one needs to retain
before even the first point is made after which we can cash in our
linguistic burden for a simple picture that fits neatly in a corner of
the mind - not even exhausting our capacity for language.

It's really like Whitehead and Russells' quasi-failed masterpiece. In
that book the same term cannot mean more than one thing. Nuances are
excluded. But, without nuances, English would require more words than
most of us could learn in a lifetime. It's less formidable to retain a
million words almost all of which are used in multiple senses that must
be distinguished from context on the fly than it would be to have ten
million words each of which were rigorously defined. An alternative
might be to do what Whitehead and Russell did, namely, construct a
lower-order primitive sub-language by restricting the meanings of the
symbols in the colloquial language we wish to use to make judgments about
the lower-order technical language we reserve for proving theorems in a
narrow technical specialty such as physics. We can't say happy
birthday, but we can show that the two statements of the Second Law are
equivalent. All of this might be facilitated by introducing several
thousand new symbols to represent relations and concepts that would be
more confusing if they were expressed with symbols that might might
recall unwanted concepts for which we have used the same symbols in the
past.

Physicists will never submit to this type of rigorous discipline. They
have been doing too well without excessive rigor. Thus, I envision
physicists like yourselves continuing to speak in a thousand tongues and
overcoming such misunderstandings as occasionally arise one way or
another. As far as teaching the discipline, you will soon enough wonder
if anyone is willing to learn it on any basis. Of course, I might be
completely wrong.

When I have finished Mallinckrodt and Leff (M & L), I will have produced
an M_&_L to Seader_and_deNevers dictionary and its inverse. I plan to
repeat this exercise between M & L and Perkins and Reynolds. Finally, if
I wish, no one can prevent me from developing a personal vocabulary that
accounts for every term in the equations I am at all likely to use. You
know, when I score baseball, the shortstop is five and the third baseman
is six. I don't care what others do. I have a private notation for
musical chords, too. The communication that is most crucial to my plans
is the one I am having with myself. Bijective dictionaries for a few
well-chosen language pairs could cary us rather far along the process of
syncretism.

My last word is that perhaps physicists might profit from a more intimate
relationship with mathematical logic. I believe we have a number of very
fine examples of the success of such relationships. And that's much more
than I intended to say. At least I didn't express my innate (at least
strongly internalized) impatience with the discussion on Heat 1 and Heat
2.

Bye for now / The Amateur