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re:Flow of energy






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From: Leigh Palmer <palmer@sfu.ca>
Newtonian mechanics is not wrong. There are many applications in
which one can produce a Newtonian solution and a relativistic
quantum mechanical approach can't even get off the ground. If you
drive a car such applications abound in your immediate vicinity.
Under no circumstances should you denigrate Newtonian mechanics
when discussing it with your students. Man could not have got to
the Moon without it!

Well I would say the Newtonian equations we teach and use ARE wrong since
they don't account for relativistic effects. To be sure, at speed domains
under 100 m/s (where most problems are formulated), these inaccuracies are
truly minute. Of course, if you take the view that F = dp/dt takes care of
any mass variance including that due to relativity, then Newton is OK in
the macroscopic domain; but normally we take Newtonian mechanics to not
include these considerations (especially when using Algebra based texts).
Once into the microscopic domain however, Newton doesn't work very well.
Nonetheless, we still teach and use Newton and as Leigh points out it works
quite well (although I suspect the NASA calculations might have included
relativistic effects--just because the computers could do it).

Above all, never denigrate anything solely because it is "not the
most current model". One need only look at the succession of
elementary particle models we've had over the last fifty years to
see the ultimate folly in that attitude. I think that cosmology
provides even more dramatic examples. Just because some thing is
New! doesn't guarantee it is Improved! It doesn't even work for
laundry soap.


This last paragraph seems to argue for care in throwing out the old and
blindly adopting the new, which is (I think) what this thread is about. To
be sure, the issue is complicated by how 'wrong' some current instruction
might be -- that is, a matter of degree rather than just a matter of right
and wrong (phlogiston is more wrong than Newton). I don't want to be in
the position of defending 'heat flow' terminology too strongly, as I don't
use it myself, but I do use energy content, energy transfer, and heat as a
noun (thermal energy), following the lead of all the textbooks I have used.
This terminology seems useful in working with the ideas of energy
conservation, of work, and with topics of calorimetry. At the intro level
almost all phenomenon being examined is macroscopic in nature and in that
domain current textbook nomenclature seems to work. I don't know that the
argument 'I can teach it right--why can't you' is valid unless the 'right'
instruction is presented to all of us in the context of the whole intro
curriculum. Doing it 'right' would seem to require that we strip those
heretical textbooks from the students hands so that they won't get confused
by reading (if you indeed get them to read) the flawed explanations.

One last comment, then I'm out of this thread. Trying to remove the
sarcasm from Van's earlier post: I really don't think the textbook authors
(at least not the whole lot of them) are so ignorant as to foolishly
perpetuate 'wrong physics'. If one WANTS to start with Classical
Thermodynamics and then be sure all the nomenclature throughout the
curriculum in consistent with the thermo, then Jim and Leigh are probably
correct. However, that's not the only legitimate way to do things
(arguments on 'heat flow' aside). I suspect the advantages of the
nomenclature wherein heat = energy, energy is transferred between objects
as opposed to work being done at every interface, and all the other points
of contention HAVE been weighed and judged to be pedagogically
superior--for the intended audience. Again, it is up to the critics to
provide a textbook (or at least rewrites of all the sections with
'incorrect' usage) that demonstrates how to do it 'right' and let the
instructional community decide if this is an improvement. 'Religious'
fervor on a topic is not enough to sway the masses (as the constructivists
on PhysLrnr have discovered).

Rick

ÿÿ re:Flow of energy