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# Re: A Parents' day gem

Date: Tue, 28 Oct 1997 15:47:33 -0500
From: NGUILBER@peddie.k12.nj.us (NGUILBER)
Subject: Re[2]: A Parents' Day gem

As much as I enjoyed it, I was a bit concerned at the outset that
relating the "Witchcraft!" incident would incite a minor feeding frenzy
among those phys-l'ers who never met a nit they couldn't resist picking.
.....
Let's remember the context, ok? This is from a *conceptual physics*
course in a *high school*, a course in which we do not treat, when
discussing projectile motion,
-> air resistance (including spin effects)
-> the curvature of the earth
-> the coriolis effect
-> the variation of 'g' with altitude
-> the uncertainties in position or momentum of either bullet
or any of the other subtleties my learned colleagues on the list
(correctly) point out. ...

I think it is good when non-trivial aspects of elementary physics courses
are emphasized on this list. I would like to thank Emillio for the example
of a glider (or a "paper airplane" pushed from a flat table). It helped me
think about an intersting aspect of falling. The same will probably be true
when I have time to meditate on what John wrote about the quadratic component
of the friction force equation. There is a lot of depth in everything and it
good to have virtual friends willing to dig for intellectual satisfactions.

Would a nonspinning disk (a strongly prolate ellipsoid) falling down
vertically hit the floor at the same time as an identical disk pushed
horizontally from the same roof? There is no "lift force" here, only the
air resistance (horizontal drag and vertical drag).

Suppose the disk is spinning (to make sure its axis remains vertical).
Does it make a difference?
Ludwik Kowalski