At 07:21 PM 1/13/98 -0800, Leigh wrote:
|>Can anyone suggest a good source for a computer demo which depicts the
|>difference between group velocity and phase velocity?
|
|Rather than a computer demo, have you a smooth-surfaced pond somewhere
|into which you might drop some rocks? Lacking that, you might just as
|well write a factoid on the board as depict the difference. They've
|seen utterly unphysical things depicted by computers on TV; why do you
|think they will put another depiction into a different class?
|
|Leigh
|
|
Sigh. The group/phase velocity distinction is one that often escapes
students, and I've found that a careful computer graphic can do wonders.
Students say "Oh, THAT'S what you mean!" You can see the light bulbs going
on. There's a big difference between that and having students memorize
factoids.
Very nice. In my mind this is the sort of thing that an instructor and
student need to have discussion over--simple student viewing isn't enough.
But animations like this, especially if the numerical parameters are under
student control, make the discussion much more productive. (example: how
would the animation change if the phase velocity were now triple the group
velocity, instead of double?)
Then, Wolfgang Rueckner wrote:
|Actually, you can also demonstrate this in a ripple tank. Float a wooden
|ruler (or any rectangular piece of wood) in the tank and give it a downward
|tap with your finger. Do this a few times to get a good sense of what's
|going on, otherwise the student just sees the water being disturbed.
This last point is critical; in any class activity the partially-engaged
student doesn't see the important detail. This is true of simulations or of
demonstrations, or even of static textbook figures.
Simulations, like figures, are really just a form of illustration. They
attempt to communicate what the model says. I still feel the argument that
since students see obviously untrue things on computer screens that they
then treat all computer graphics are suspect is specious. *** There's a huge
difference between presenting one aspect of a model of reality and
presenting a cartoon. Students ARE sophisticated enough to recognize the
difference. (How do I know this? By asking students.)
***Try this version: Since most student have seen magic shows, they will
automatically distrust all physics demonstrations. Why would they see any
difference?
As we continue to discuss the utility of simulations, remember that they are
only one SMALL part of the total mix of a physics course. They, along with
demonstrations, experiments with simple measurement tools, experiments with
complex or computer based tools, homework problems, readings, discussions,
and yes, even lectures (short!) are means of connecting with a student.
Simulations are not magic bullets, but then neither is learning to program
in (your favorite programming language here).
Finally, Joel wrote:
|I take some offense at
|the idea that 10 or 20 or 30 years of classroom experience doesn't
|constitute legitimate experience (experience) for pontificating on
pedagogy,
|just because some statistics and journal articles weren't written based on
|the said experience.
True enough. I think I was being overly careful, perhaps in response to the
extreme we saw recently from one who "knew it to be true" and needed no
proof that rock and roll causes brain damage. (but let's not start that one
again!)
Enjoying the discussion,
JEG
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John E. Gastineau mailto: gastineau@mindspring.com KC8IEW
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