Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Explaining




-----Original Message-----
From: Raacc@aol.com <Raacc@aol.com>
To: phys-l@atlantis.uwf.edu <phys-l@atlantis.uwf.edu>; Raacc@aol.com
<Raacc@aol.com>
Date: Friday, February 20, 1998 3:14 PM
Subject: Re: Explaining


In a message dated 98-02-20 12:34:00 EST, Bob Sciamanda writes:

<< At the introductory level, I also "derive" the ideal gas equation by
specifying N/3 point molecules travelling with the RMS velocity in
each of the three Cartesian directions. (A commonly exploited
simplification - and illumination).
>>
Bob,

I have no objection to using simple models. My response to this post
was more
to the origional poster, from a different thread, that I misplaced.
Thanks to
Leigh, I was able to respond anyway.

As I recall, it dealt with the student misconception that resistor
heating was
a result of electrons losing kinetic energy. I was simply trying to
explain
that while this may be a misconception if you stick to a certain model,
it may
be a valid consequence with another model. How is it then possible to
say if
the student's response was a misconception, or if they may have given
more
detailed thought to the problem? Only by communicating with the student
I
presume.
Bob Carlson

********************************************************
Bob Carlson makes a humanizing point here which is easily mis-stated and
mis-interpreted, but whose useful wisdom only comes with the mellowness
of age (or at least experience). If I proceed cautiously, I would go
even farther:

When younger, I would fight with youthful vigor and passion (at least
internally) every mis-conception or badly limping model of students,
teachers, engineers, authors, etc. With the mellowness and hopefully
increased wisdom of age I see even more clearly the errors of these
mis-conceptions (including my own), but more importantly I also see that
my adamant objections have often been mis-spent.

We all construct our own models and fit them to be of use for as far as
we can (or perhaps plan to) see. If someone sees farther (or wider) they
will construct different models. Each has its own use; the hammer for
putting up dry-wall, the sledge hammer for laying railway track.

A case in point is the mechanism by which electrons in a current carrying
wire are impelled: 1) the electrostatic field of surface (and other)
charges, vs 2) the forces of moving electrons pushing those ahead of them
out of the way (hydraulic, or billiard ball model). Even when the books
preached 1), graduate engineers conveniently thought 2) for their entire
lives. I became especially concerned when textbooks began to become mute
on this subject (although at the same time equations like j = sigma*E
began to come down into introductory books). Now 1) is on its way back,
which I applaud.

But now I try to calmly and dispassionately ask myself: Who cares?
(More sanely, when should one care, and to what extent?) If it does not
lead to the faulty design of a bridge, or to some other bad engineering,
it is harmless and perhaps even useful.
(True, it may lead to bad thought, but he will never see that far.)

Now I consider that the "useful misconception" can be very much like a
mnemonic: a useful representation, an algorithm of calculational value.
Feynman playfully tells (in QED) how he teaches grad students to rotate
arrows and place them end to end to solve a QED problem. RF draws a
parallel between these QED calculations and the enigmatic Mayan
calendar/eclipse algorithms. His point is that the calculational
procedures work; what they mean, and why they work, is something else.
Students might hang dozens of representations (mnemonics) onto that
algorithm. Take away the (presently accepted) phasor meaning, and the
procedure is just as useful.

My criteria for "best model" (heavy in far reaching intellectual
consistency), are quite different from the typical engineering student's
criteria (heavy in easy applicability to a narrow scope of problems). As
I have stressed elsewhere, I believe that we have already crossed that
conceptual barrier beyond which no single human model can usefully
represent all aspects of reality (eg an electron). I have no doubt that
the more we learn of reality the larger will become our repertoire of
models needed to describe the same reality under different circumstances,
in human terms.

Bob Sciamanda sciamanda@edinboro.edu
Dept of Physics trebor@velocity.net
Edinboro Univ of PA http://www.edinboro.edu/~sciamanda/home.html
Edinboro, PA (814)838-7185