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Re: ENERGY WITH Q PLEASE VOTE



at the risk of ridicule, I'll comment: When one bends (or rolls, etc.) a
typical metal sheet it becomes warmer. However, the process also adds defects
-- defects "are" potential energy. i.e. upon annealing one will find the
"internal energy" increase in the metal is greater than the amount added by the
annealing process. So is the defects energy internal energy? A la number 2?

bc

P.s. I think students should be introduced to #3 (along with history of
caloric, phlogiston, etc.), then once enlightened they may use 1 & 2 as
appropriate.

P.p.s. Also how does one "handle" state changes?

kowalskil wrote:

I am not in favor of voting. Good comments are much more
useful. You presented these alternativews:

1) heat is energy transfer due to temperature difference?
2) heat is internal energy or thermal energy?
3) heat is not a noun?

I would not say heat is internal energy, it is part of
that energy (which is often transferred due to a temperature
difference). It is also energy which appears when mechanical
energy decreases due to friction-like forces. It is also
energy which appears in some chemical reactions. It is also
energy which appears when fission fragments are stopped in
nuclear reactor. It is also energy which appears in a
microwave oven. It is also ...

In calorimetry we define heat in terms of what it does
to water, not in terms of what model we use. That was a
very productive approach.

If heat is a form of energy then it is a noun, like
kinetic energy, or like momentum, or like force, or
like velocity, or like .... What is wrong with this? I have
nothing against a different word for the same concept. But
for the time being I will use heat.
Ludwik Kowalski

Larry Smith wrote:

At 3:44 PM -0500 11/9/01, Carl E. Mungan wrote:
From what I have heard on PHYS-L and elsewhere, I suggest the
following basic definitions of heat:

1. Heat is the energy transferred between two bodies owing to their
difference in temperatures. This energy can be transferred by
conduction, convection, or radiation. The canonical example is a hot
plate warming up a gas, where the system is the gas. The heat
transfer can be either reversible or irreversible. If reversible, it
equals the integral of TdS. If irreversible, it is possible to
construct an equivalent hypothetical reversible path between the same
initial and final states of the system, such that the integral of
dQ/T for that process equals the entropy change. At the risk of
agitating some members of this list, I believe this is the
conventional definition found in most texts of either intro physics
or advanced undergraduate thermo and it is the view I prefer.

2. Heat is internal energy, or possibly just certain forms of
internal energy called thermal energy. Heat therefore does not
necessarily get transferred from a hot body. For example, the
adiabatic compression of an ideal gas produces heat in the gas
because the gas warms up. For more general materials, heat is also
produced during phase changes. The heat of an isolated body is time
dependent in general - for example, a rotating fluid initially
possesses mechanical energy but viscosity slowly transforms that into
heat. Heat is the integral of TdS regardless of whether the process
is reversible or irreversible. Hence, in a free expansion of an ideal
gas, heat is positive since the entropy increases, despite the fact
that the gas temperature is constant and the system is isolated. This
appears to be Ludwik's view in at least some parts of his document.

3. There is no such thing as heat. I know what energy is. I know what
work is. Heat is just a special kind of work applicable to specially
contrived problems. So who needs it? Certain list members seems to
hold this view. But they can and have spoken for themselves.

If we were to take a vote could everyone vote for one of these choices?
Has Carl stated them satisfactorily? Are there other candidates?

Let's take the vote.

How many think 1) heat is energy transfer due to temperature difference?

How many vote for 2) heat is internal energy or thermal energy?

How many vote for 3) heat is not a noun?

I think we're pretty sure Jim Green, Leigh Palmer, and the editor of AJP
vote for #3.

Lots of freshman textbooks seem to be in the #1 camp.

I don't necessarily think physics can be decided by democratic vote but
maybe definitions and conventions can (over time). Are all three choices
equally good as long as we're individually clear to our students, or is
there virtue in all teaching it the same way? And if it is good to all
teach it one way, is one of the three choices above clearly better (at
least pedagogically)?

If Jim Green is right but in a small minority, is it worth the trouble to
change the freshman textbooks? My opinion is that yes, it is worth the
100-year effort it will take to reform our usage if it is in some sense
more correct or pedagogically preferable.

To those who disagree with Jim Green: do you disagree that #3 is correct,
preferable, or more clear (please read his web page about the first law at
<http://users.sisna.com/jmgreen/>); or do you just not think it worth the
effort to change even though he be right?

Cheers,
Larry