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Re: HEAT1=HEAT2 ?

The problem is that we confuse the students in high school physics. We
cite the Rumford experiments to prove that heat is not a substance
(phlogisten) and then use the outmoded idea of adding and subtracting
heat when we teach calorimetry.

Herb Gottlieb from New York City
(Where we exchange stocks and bonds rather than heat)

On Tue, 26 Aug 1997 11:36:10 -0500 "Richard W. Tarara"
<rtarara@saintmarys.edu> writes:
I would certainly vote for leaving the usage of 'heat' alone in the
introductory texts. If there really is a concensus, then perhaps some
pressure could be placed on the writers/editors of 'University
Physics'
texts for more 'precise' use, but leave the 'College Physics' and high
school texts alone. It seems to me that to limit the usage of 'heat'
to
the classical thermodynamics meaning would only obfuscate the topic
for
non-majors. For these beginning students, we need to work from their
experiences and their vocabulary and the common treatments in
introductory
texts tend to do this.

As far as changing the word in thermodynamics, if we think physics
majors
are too dumb to understand that 'heat' has a much more restrictive
meaning
in this context, then we could change it.

Rick
----------
From: LUDWIK KOWALSKI <kowalskil@alpha.montclair.edu>

Yes, the word heat has two conflicting meanings in many introductory
physics
textbooks. In thermodynamics it refers to that part of a thermal
energy
change
which is due to a difference of temperatures, dT, between the inside
and
outside of a system. It is a path-dependent quantity, usually
expressed
in
joules. In elementary physics on the other hand, heat is the name
given
to
the quantity Q when the formula Q=c*m*dT is used to perform simple
calorimetric calculations. Students often say that the temperature
of a
body
is determined by the amount of heat "it contains". Phrases such as
"heat
added
to a body" or "heat removed from it" are commonly used by teachers
who
take
it for granted that "heat" is a synonym for "thermal energy of
molecules
and
atoms". The experiments of Joule are often interpreted by saying
that
"energy in the form of heat" and "mechanical energy" are
equivalent. In
thermodynamics, on the other hand, we emphasize that heat is not a
state
function, such as energy or enthalpy.

Thus a common statement: "heat is a form of energy" is false in
thermodynamics.
This situation was created because the same name, "heat", was given
to
different physical quantities expressed in joules. We use it in
calorimetry
and we use it in the first law, dE=Q+W. The recognition of this fact
is
an
important first step toward the elimination of many conceptual
conflicts.
We
must then decide what to do about this unfortunate situation. Should
the
term
"heat" be eliminated from elementary calorimetry and replaced by
"internal
energy"? I suspect that most phys-L-ers would favor this "modern"
approach.
They would disagree with the following formulation, found in Sears
and
Zemansky. "The process of combustion releases the internal energy
and
converts
it into heat. In this form the energy can be utilized for ..."

The other alternative is to retain the traditional meaning of heat
(form
of
energy) and to invent a new name, for example, "thermal
pseudo-energy",
for
the path-dependent quantity Q in thermodynamics. This approach could
be
defended by observing that "heat" is a common word; introductory
courses
have
traditionally been structured to quantify common words, such as
force,
work
and heat. Phrases, such as "energy in the form of heat", "heat
released
in a
reaction", "heat produced through friction" or "heat flows" are too
deeply
rooted to be abandoned. Renaming Q in thermodynamics would be less
confusing
than renaming it in elementary physics. Wouldn't you agree with Jim
that
the
most effective way of confusing students and teachers is to redefine

traditional words with which they are already familiar. Can students
learn
thermodynamics before they learn calorimetry?

By the way, I still think that a distinction between thermal energy
and
internal energy can be very useful in many problems. Thermal energy
is
that
part of internal energy which is associated with motions and
interactions
of
molecules and atoms. The internal energy, on the other hand, is not
limited
to its thermal component; part of it may be associated with motions
and
interactions of macroscopic components of a system, such as wheels,
belts,
springs and pistons. 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
Kowalski