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Re: Insulation/temp gradient



( I reviewed my offering written here, and had real difficulty in
deciding whether to delete it or hit the Send button.
I fear I cannot contribute much of value in the heat debate -
the topic is so loaded, it seems. )


At 15:07 9/7/97 -0400, Bob responded to this:

Brian wrote:
. . .
If you will forgive yet another electrical analogy, it is evidently
a comparable situation to a string of resistors in series.
. . .

[Bob]
Has our discussion about precision in language made analogies something
odious? Then we have lost something valuable. There is nothing to
apologize for. It would be a disservice to our students NOT to point
out such "analogies"; ie., cases where the same mathematical model is
commonly used to describe two or more different phenomena.

[Fred]
...we end up treating students like parrots. We have students
name the phases of the moon on a test. Who has time, or will take the time,
to EXPLAIN or DEMONSTRATE how two spheres revolving around each other
illuminated by a third, distant sphere interact. What teacher asks a
student to EXPLAIN something on a test.
Those who promote the teaching of Science primarily through
mathematical modelling are responsible for this result. There is no time
left for physical or conceptual modelling. Only a tiny fraction of 1% of
people see any meaning in a mathematical model. Yet it is the PRIMARY
teaching method used in many science courses.

Fred Bucheit


I think Fred might note that an inverse square law used to describe
force due to charge and force due to gravitation could well lead
students to expect a similar physical mechanism.
Gravitational force is however described as a distortion of an ether:
(it is not of course called an ether in this century, just 'space-time.')

Where is the teacher who offers the idea that electric force could also be
described by a 'distorted ether' model, but is not because we have chosen
otherwise?



(This is surely not a purist's analogy - to compare dV and dT is not
quite respectable...) . . .
brian whatcott <inet@intellisys.net>
Altus OK


One of my concerns with this analogy was the unipolar nature of temperature
compared with the bipolar nature of electrical potential.
There is a comparable difference between gravitation and electrical
potential in this respect. I would rather have teachers stress the physical
model rather than the purely mathematical formalism.
Maths is not physics.

[Bob]
Physics really has only a few basic mathematical models, and not many
more (maybe fewer) basic conceptual models. It is an important part of
our physics to realize that reality is something beyond all of these
models, and to notice that in our analyses one and the same mathematical
model may be paired with different conceptual models to describe
different phenomena. Part of our understanding is to notice, appreciate
and ponder (surely not disparage) the analogies that result.
--
Bob Sciamanda

This seems like a balanced, measured statement of the position.
So am I the only one who registered the cries of anguish when I
suggested the virtues of analogies in this list some time ago?

And am I misconstruing the very real anguish expressed by the
people with insight into thermodynamics, when the verb 'flow' is
used in connection with the word 'heat'?
Electric current certainly 'flows' in the useage of most users
of electrical units.

But the discussion on heat is now so distressed (again?)
that radiative, perhaps even conductive heating is said to be
a 'work' issue, as quoted below:

[Ludwik]
The energy related threads made me aware that thermodynamic heating
(a process by which the internal energy of a system is changed due to a
difference of temperatures between the inside and outside) should not be
confused with "pseudo-heating", for example, when a penetrating radiation
(alpha particles, electrons, photons, etc.) is entering a system...


(Surely PHOTONS are the transfer mechanism for heating???)

With apologies in advance if I have succeeded in stirring
pointless debate or muddying the water, so to speak.
brian whatcott <inet@intellisys.net>
Altus OK