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Re: [Phys-L] heat content

Consider an over-and-under water pistol/dart gun (no, I've never seen one either) at a temperature of 25 degrees Celsius, cocked, loaded with water, spinning, and moving through space relative to the observer's reference frame. The pistol has spring potential energy, kinetic energy of translation, kinetic energy of rotation, electrostatic potential energy associated with interactions at the atomic level, and kinetic energy associated with the motion of the atoms and electrons within the material making up the object. Now consider the object to be in thermal contact with surroundings at a lower temperature than the object. The object radiates energy away in the form of infrared radiation until it comes to a temperature of -5 degrees Celsius. I am open to change, but at present, I would call that atomic-level energy that the object had, but later got radiated away, "thermal energy". I'd consider calling it "internal energy" but I'd be concerned that some people might include the energy of rotation of the object about its center of mass as well as the spring potential energy of the object in their definition of "internal energy," in fact, doing so seems reasonable to me. I consider the thermal energy to be the energy that could (and would) be transferred to a colder object just by bringing the object in question into thermal contact with that colder object. Note that it includes both the kinetic energy associated with the motion of the atoms and the electrons and the potential energy associated with interactions at the atomic level. I think that categorizing energy in terms of the way it manifests itself--a compressed spring, translational motion of the center of mass of the object, rotational motion of the object about its center of mass, and the phase and temperature of the material making up the object, comes in handy. I don't see any contradiction between categorizing energy in terms of the way it manifests itself and the fact that energy is energy. I don't see a problem with using the expression "thermal energy."

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Friday, February 07, 2014 7:52 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] heat content

In this message, I am not talking about politics, public policy, planets, oceans,
climate, or weather. I'm just talking about basic principles of
thermodynamics.


On 02/07/2014 03:13 PM, Robert Cohen wrote:
Just curious but does it bother anyone that NOAA refers to the "ocean
heat content" as opposed to "ocean thermal energy content" or some
such phrase?


Well, many physicists see the word "heat" as a red flag.

Speaking for myself, I see something like the red flag
in the diagram shown below: A guy is standing on top of
Mt. Baldy during a raging thunderstorm. He is holding
up a tall metal pikestaff bearing a little red flag that
says "heat".

Very indirectly, the flag might call attention to the fact
that the guy is doing something stupid.

HOWEVER ... changing the terminology on the flag isn't
going to solve the problem. In particular, changing it
to say "thermal energy" is no improvement whatsoever.

The problem is with the physics of the situation. Making
the terminology more politically correct will not change
the physics of the situation.

Some non-metaphorical discussion appears below the diagram.


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In physics, the word "heat" is used with at least four or five
different technical meanings ... and that's not even counting
the various non-technical, metaphorical, and/or jocular usages.

We are dealing with just one of the usages here, namely "heat
content" ... which for present purposes is exactly synonymous
with "thermal energy content".

The problem is, these terms refer to something that does not exist,
except possibly in trivial cases. It does not matter what you call
it. You can call it "heat content" or "thermal energy content" or
"caloric" or whatever ... and it still does not exist. The basic
rule is that energy is energy, and "thermal" energy cannot be
distinguished from any other kind of energy. This has been pretty
much known in the literature since 1798, although that's not the
whole story.

The other part of the story has to do with /entropy/.

When somebody says there is too much heat in the ocean or anywhere
else, they might mean that there's too much energy, or too much
entropy, or quite possibly both. It should be obvious that you
cannot use one number ("heat content") to quantify two things
(energy and entropy). I guarantee that choosing a more politically-
correct name for this one number will *not* solve the problem.

For the tiny minority of people who care about the history of
science, we note that there is precedent for this. The idea
of "phlogiston" was widely used in the scientific community,
and remained in use for many decades even though it was known
to not fit the facts particularly well. There were many attempts
to replace phlogiston with something else, but none met with
much success until it was realized that phlogiston had to be
replaced by *two* ideas, namely energy and oxygen.

So it is in our time. The whole idea of "heat" is as dead as
phlogiston. "Heat" needs to be replaced by two ideas, namely
energy and entropy. Trying to quantify the "heat" is a fool's
errand. Don't do it. Quantify the energy and entropy instead.

BTW this is one more nail in the coffin, as if any were needed,
demonstrating that you can't believe what you read in the PER
literature. I'm referring to the holy wars over how "heat"
supposedly "must" be defined ... plus long, detailed disquisitions
on how to explain irreversibility in terms of energy, et cetera.
People who have some understanding of the actual subject matter
hold their noses and run away screaming.
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