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



I have some problems with Leigh's characterizations below. First of all,
with the demeaning tone taken towards some of the contributors to this list.
I've discussed this before both on and off the list. The 'curmudgeon'
approach isn't as useful today as it might have once been. I suspect Leigh
gets away with it in the classroom exactly because of his age, but I suspect
if younger instructors try this tact with students they might well find
their evaluations and chances for tenure somewhat at risk! I give up hoping
that Leigh will be more moderate--on the other hand, maybe he has been ;-)

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. I also have serious doubts that the many 'people with knowledge
of small arms ballistics' know much more than that the site adjustment is
not necessarily linear with muzzle velocity. At least, I doubt there are
very many people who know enough about the ballistics to object to the
simplified trajectory model used in introductory courses on a sound physical
basis.

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.

Rick

-----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