Ok, folks, educate me. I've read all this pussyfooting around the subject
of inertia demos, but no one has yet said what, exactly, students LEARN
about INERTIA from such demos. I haven't a clue. What physics do they come
away with that's useful in other situations? Keep it simple and spell it
out clearly so my feeble brain can comprehend. Convince me that this
tablecloth demo, as usually done, has *any* educational value.
These arguments *don't* convince me, so you'll have to come up with
something better:
(1) It shows that a body at rest remains at rest until acted upon by a
force. (It doesn't show that at all, for the cloth *is* exerting a force,
and a considerable one, on the bottom of the objects. Yet they remain
essentially at rest. At least you hope they remain at rest.)
(2) It demonstrates that bodies with more mass (inertia) are harder to
move. (As these demos are usually done, all bodies, even with different
masses, do not move much, and any differences can't be readily noticed.)
(3) It demonstrates F=ma. [Huh? Exactly how?]
(4) It demonstrates that if you do something to objects quickly enough,
they won't notice. [I like this one, for it is consistent with what is
observed.]
(5) If you don't see the point of this demonsration, you don't understand
inertia. [Widely used, but it *may* indicate that the one who uses this
line doesn't understand it well enough to explain it, or the thing may
be more complicated than it appears, or it doesn't really demonstrate
the point intended very well.]
(6) Observing *anything* is good education, even if students don't
understand all the physics behind it. [I don't entirely disagree. But I
have a reservation. In one of those required liberal arts courses we all
have taken I recall a quote "The unanylized life is not worth living."
[Who *did* say that?] I submit: "The unanalyzed physics demonstration is
not worth doing, or watching."
Better yet, I challenge you to try this:
Do the tablecloth-yanking demo for an ordinary class of college freshmen,
or your honors high school class. Or do one of the other simpler forms of
it previously discussed.
Ask them to write a short essay or paragraph telling what they learned
about inertia from the demo. Ask them if the demo taught them anything
else about physics.
I think you will be surprised/shocked/apalled when you read the responses.
If you get any good, or outrageous ones, please share them with us. We
should seek this feedback more often after we do demos.
BTW. I notice that Freier and Anderson's book _A Demonstration Handbook
for Physics_ has two categories: "Inertia of rest" and "Inertia of
Motion." They put the tablecloth demo in the first category. As you know,
they explain nothing in this book, and seldom give any instructions for
effective presentation.
-- Donald
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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
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