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Re: Old guitar strings--actually Leigh's comments



On Wed, 5 Nov 1997, Richard W. Tarara wrote:

I have some problems with Leigh's characterizations below.

As a card-carrying curmudgeon myself, I found Leigh's comments (below) to
be quite moderate, fair and restrained. They were also worthy of thinking
about. Too often we physicists come across as ivory-tower dogmatists who
are contemptuous of the 'practical arts' and ignorant of them as well. On
the one hand we are seen as oversimplifying some things, and
over-intellectualizing others. We should be aware of these perceptions and
do what we can to deflect them in advance.

First, we look up from time to time from our textbooks and make contact
with the real world we claim to be talking about. When we idealize a
situation, it doesn't hurt to say so, and point out (briefly) in what way
we are idealizing, and why. We shouldn't make statements in a dogmatic
manner, such as "the trajectory of a bullet is a parabola" (wrong on at
least five counts). Worse yet is to expect students to parrot back
incorrect slogans and dogmatic assertions on exams.

What I really take exception too is that the teacher was 'overreaching his
competence'. The fundamental principle in the instruction has to do with
the independence of the gravitational force and the horizontal motion. To a
very good approximation, this principle is upheld in projectile motion up to
the point of using very high velocity bullets and/or bullets that tumble.
The 'nit-picking' that has been going on about the true behavior of 'real'
bullets isn't really relevant to the original message. Clearly the parent
objecting to this description WAS NOT invoking any of the subtle arguments
about the motion of projectiles through a viscous media with spin and/or
tumbling.

Yes, this point seems to have been missed. No one enlightened us on
exactly *why* the parent was furious.

While I sympathize with the desire to make the physics we teach applicable
to the everyday world around us, there is a fine line between being accurate
and complete and being totally opaque to the students. Again, this
discussion falls back on model building and defining the limits of
applicability of any given model.

There's an even more fundamental pedogagical principle we should remember.
Never attempt to *teach* something you don't know fully, in detail, and at
a level well beyond the level of the course. If in doubt, leave it out.
One of the marks of an educated person is to know the limits of one's own
knowledge and understanding (and there always are limits). Worse than "not
knowing" is "knowing things that aren't so".

-- Donald

......................................................................
Dr. Donald E. Simanek Office: 717-893-2079
Prof. of Physics Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745 CIS: 73147,2166
Home page: http://www.lhup.edu/~dsimanek FAX: 717-893-2047
......................................................................


-----Original Message-----
From: Leigh Palmer <palmer@sfu.ca>

Physicists are usually ignorant of such real world oddities as these.
That is the kind of ignorance which leads to interactions that annoy the
man in the street (who may be knowledgeable in some art or craft). An
example came up recently when a teacher overreached his competence in
suggesting that bullets dropped vertically and fired horizontally fall
at the same rate. People with knowledge of small arms ballistics (many
of whom never take standard physics courses) know that is untrue. The
disease even manifests itself more dramatically when physicists try to
put other fields, some of which are doing nicely already, on a "proper
scientific" foundation. An example is the introduction of "scientific
pitch" based on a middle C frequency of 256 Hz to make calculations
easier for even tone-deaf physicists!

Leigh