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
student I'd had about 20 years before. He immediately recalled the
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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