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heat is "real", but...



On Wed, 31 Jan 2001, Larry Woolf wrote:

"When you grasp that heating is a way of doing something and abandon all
attempts to identify heat as an entity, especially a vague, metaphysical,
even paranormal entity, you can think more clearly about thermodynamic
problems. We know of no examples in which invoking a mythical substance
called heat leads to increased physical understanding."

Hmmm. Sounds like a straw man argument. And should we also say that
sound is "not a noun," and neither is light, because there are no mythical
SUBSTANCES called sound or light?

But who insists that "heat" is a substance? Perhaps words are being put
into the mouths of the "heat believers" to make their viewpoint look
foolish. Heat is only "substance-like" in that it is a conserved
quantity in some circumstances. If "heat" is composed of the KE of matter
plus the IR light which propagates between molecules, then "heat" is very
similar to "sound" and to "light." As a matter of fact, it is nothing
more than a mixture of sound (chaotic mechanical vibrations) and light
(radiation emitted by warm materials.) Photons + phonons = 'heat.'

On the other hand, I think that "heat", while a useful concept, is still
misleading in many ways. Hot objects put out thermal radiation, but
should we say that their internal "heat" has been CONVERTED into thermal
radiation? No, because the "heat" within a solid object is partly MADE of
the same kind of thermal radiation which escapes from its surface.
Similarly, when sound is absorbed by an object, does the sound change to
"heat?" No, the sound simply raises in frequency, becomes turns broadband
(like white noise.) Also, it's easy to get the wrong impression that
infrared light is made of "heat", while visible light is not. As if a
white-hot iron poker isn't full of visible light within its surface!

Pour high-frequency white noise into an object. Pour bright light into
the same object. The object contains "heat"; it contains photons and
phonons which are constantly trading places as they are each absorbed by
molecules and reemitted in the other form. Touch that object to a cold
one, and "heat" flows from the hot one to the cold one. What flowed?
High frequency sound, and invisible light. (Well, if a white-hot poker
touches another bit of iron and heats it red hot, then VISIBLE light also
flowed between the objects.)

This "heat" stuff is real. But it's too darned complicated to understand
easily, and it usually leads to misconceptions. Rather than trying to
make a law that says HEAT IS NOT REAL, we instead could accept that heat
IS real and end the fighting. And then fight instead about why "heat" is
too complicated and misleading to introduce at the N grade level.


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