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Re: heat is a form of energy



On Wed, 8 Sep 1999, Leigh Palmer wrote:

At 8:49 AM -0700 9/8/99, William Beaty wrote:

...and Newton's laws are cognitively flawed because they don't incorporate
relativistic concepts. They have limited application. We should stop
using them?

Explain to me how they are cognitively flawed. I'm unaware of any
problem there.

Newtonian mechanics directly implies that there are no "speed limits"
placed on relative motion, and also that time and mass behave in a
Classical manner. Therefor Newtonian mechanics is horribly misleading,
and we should not teach it. Instead we should wait until the undergrad
level, and then teach SR and GR directly, when no "Newtonian" concepts
intefere, or need to be unlearned. (Playing devil's advocate here. In
reality I think we should teach Newton's laws. And "heat". And also the
Bohr-orbital or "solar system" description of atoms. And then later
supply the information that lets students modify and extend these
concepts.)


"Heat" works fine as long as we remain extremely aware of its limitations
and of the misconceptions it can breed (no, I myself am not yet totally
aware of these. I'm still learning thermo and trying to assemble an
intuitive picture of entropy concepts.)

By implication you are telling me that "heat" works better than
"energy" in some application of the pedagogy. Please give me an
example; I can't think of one.

I see that "heat" is the same as "energy", within limits. Call it
"thermal vibratory energy" or call it "heat", and we communicate about the
same concept. I'm debating Jim Green in this thread at the same time, and
I suspect that he would strongly object to our replacing the noun "heat"
with the noun "energy" and therefore claiming that "energy" flows from a
hot object to a cold one.


Touch a warm copper block to a cold one. "Heat" flows. The "Heat flow"
concept is a useful mental tool. Do you have an alternative set of
concepts which can be understood by students/teachers in the lower grades?
Or should we remove Thermo from curriculum material below the undergrad
level?

If you want to use the analogy why can't you say "energy flows"?


I can! I thought I was not allowed to say this. "Energy flow" is being
attacked too, but apparantly you aren't part of that fight?


Also, incoming students already understand "heat flow". If we ban the
word "heat" and give bad grades if they use it, then the students might
come to think that "thermal energy" is a different animal as compared to
"heat", and that two different types of energy exist here.


In
what way is it better to say "heat flows"? If there is a difference
(as the use of a different term would imply) what is it?

Well, let me see. Light propagates. Electromagnetic energy propagates.
Does this confuse students? Should we ban the word "light", and instead
say that only "EM radiation" is real, and regard "light" as an unnecessary
and confusing entity which doesn't really exist? I think the same
situation applies to "Heat". "Heat" in solids is oscillatory energy
stored in atoms, but just because we can call it "Oscillatory atomic
energy", doesn't mean that we should ban the term "Heat."


Would you
similarly speak of the flow of work into a copper block being
pressed into a belt sander, or the flow of work into a descending
yo-yo?

Sure. If "work" (noun) is defined as a conserved quantity which can be
stored in a pendulum or a spring or a flywheel, then heat and work are
basically the same thing, only the frequency is different. Analogy: if I
run my finger across a row of non-swinging pendlulms and leave them all
crazily swinging, my finger experiences a sort of semi-constant friction
as it moves down the row. At the same time the pendula receive and store
high-frequency energy. This is a simplified model of how frictional
heating takes place, and how low-frequency macroscopic mechanical "work"
is converted into high-frequency "stored heat" via a frictional process.


Heat and work are processes. The name for the quantity of energy that
is associated with each process has the same name as the process, an
unfortunate feature, in my view.

If "heat" and "work" are verbs, then they are processes. If they are used
as nouns, then they are more like conserved substance-like quantities.

Inject "work" into a capacitor by connecting it to a hand-cranked DC
generator and then cranking the handle. Now disconnect the capacitor and
throw it across the room. "Work" has been transferred. Now connect that
capacitor to a DC motor on the other side of the room, and the "work" can
be used to lift a mass attached to a windlass. Throw the de-energized
capacitor back and repeat the process continuously, and we have flow of
"work" taking place.

If this whole controversy is about whether we should allow "work" and
"heat" to be defined as nouns, then this controversy is Swiftian:
the bigendians want to expunge the littlendian heresies, while ignoring
the fact that both opponents are greatly in favor of cracking that egg and
getting to the important stuff inside.


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