Date: Thu, 28 Sep 2000 10:31:51 -0500

Author: Laurent Hodges

Subject: RE: Classroom demonstrations: education or entertainment?

Post:

>Analysis of the performance of different student groups
>shows that students who do not see a demonstration fare no worse than
>students who are shown the demonstration in the traditional way. The data
>suggest a small improvement in performance when students have to predict
>the outcome of a demonstration before seeing it.

One of my favorites is the large wooden yo-yo with a stout string attached
to the axle. Show the students the yo-yo and sketch its construction on
the board just to be sure they understand it. Put the yo-yo on the table,
hold the string straight up, and ask what will happen when you pull the
string up: the string unrolls and the yo-yo remains on the table, rotating
some; the yo-yo follows the string up centimeter for centimeter; the yo-yo
rolls up the string. HA-HA-HA: of course they know what will happen. The
class gets this one 100%.

Then repeat with the string horizontal. HA-HA-...-hmm. Maybe not so sure.
The class is divided on this one.

Finally show them that holding the string out at the correct intermediate
angle will cause the yo-yo to slip on the table without rotating.

Another demonstration: Once on an out-of-town trip I met by accident a
pleasure demonstrations had given him and said his favorite was the
mechanical analog of the Doppler effect. On this one we have a long, long
motor-driven string across several tables, moving in a loop about a pulley
at the far end. We have white paper "riders" (long slender pieces of paper
folded at the midpoint) that can be dropped at regular intervals (using a
metronome) while the demonstrator stands still, moves with the string, or
moves in the opposite direction, to model the change in wavelength. I
remember being a little surprised that he remembered that particular
demonstration so long afterwards, but apparently it made quite an
impression on him.

Laurent Hodges

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