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Re: A Parents' Day gem

A postscript to the recent discussion on which concepts to begin the year
with in physics ...

We had Parents' Day last weekend at the boarding school where I teach.
my end, it went by without a hitch. However, the teacher in the classroom
to mine, a veteran educator who teaches a conceptual physics course, was not
quite so fortunate. His course had been studying projectile motion recently,
and apparently one of his student's parents was not at all pleased with
what my
colleague had been teaching.

The parent became very agitated. In the Q/A period after a presentation,
he exclaimed, "I hear you are teaching WRONG THINGS in this class!"
The teacher replied, "How so?"
"Well," the parent charged, "my son had an assignment recently where YOU
were teaching that a bullet FIRED from a level gun and a bullet DROPPED from
the gun when the shot was fired will both hit the ground at the SAME TIME!"
"It is not I who teaches that," the teacher responded. "The laws of
physics teach you that."
"That's LUDICROUS!" said the parent. "ANY fool can see that the forward
momentum of the SHOT bullet will make it spend LONGER in the air that the
DROPPED bullet!"
"I can prove it to you mathematically if you wish," replied the teacher,
"but they will, in fact, hit the ground at the same time."
A pause. Then:
"This is witchcraft!" the parent hollered. "WITCHCRAFT!!!" And he
and stormed out of the classroom.

This really happened.

No word yet on whether or not the kid has dropped physics.

A previously undiscovered occupational hazard, apparently, with starting
your year with kinematics! 8-)


Nick Guilbert

The Peddie School
Hightstown, NJ

The first question that pops into my mind is, why didn't he do the demo to
show that they hit at the same time (at least for low velocity situations)?
Offering to mathematically prove the result just adds fuel to the fire. A
demo puts it all to rest, and once the parent calms down, then the caveats
can be added.

But of course in the case of a real bullet fired from a gun, they don't hit
at the same time, because there are all sorts of things that get in the
way, like the curvature of the earth, the interaction of the spinning
bullet with the air (I don't know exactly what this does to the bullet, but
its a fair uess that it does something), wind or air currents, any slight
misalignment of the gun with the horizontal as the bullet leaves the
barrel, and others that I can't think of right now.


To get random signatures put text files into a folder called "Random
Signatures" into your Preferences folder.The box said "Requires Windows 95
or better." So I bought a Macintosh.