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Re: [Phys-L] long-range forces, short-range couplings



We start with an easy question: How can you have a
"long-range" force at all, given that special relativity and
basic notions of causality require everything to be local in
space and time?

But students have no clue about relativity and its ramifications. They have
to work their way up to it, not start with it as the first idea. Since
students think in an Aristotelian or perhaps a medieval fashion they have to
first discard their non-Newtonian concepts.

That is where interactions comes in. The basic concept is not nebulous,
because one can readily see that motion is changed in an interactive
fashion. Research has shown that introducing the concept of interactions
before NTN3 improves student understanding of NTN3. The use of interactions
is instead of action and reaction. The latter terms are very loaded.
Students already have a concept of action and reaction as what happens, so
when you jump off of a boat they clearly see that the action (jumping) is
much bigger than the reaction (boat recoil). So they form the idea that the
forces are different on each. But using interactions gets away from that
already formed paradigm by using a different word. At that point NTN3 can
be understood much better. Actually many students have the idea that when
you push on a wall, it doesn't push back, and again establishing the idea of
interactions helps them understand that.

If I were to explain how short range coupling can result in long range
interaction, the students would think I was using double talk. It is like
the far side cartoon showing what the master thinks he is telling his dog,
and what the dog percieves. To them it would be gobbledy-gook. Actually
understanding is built by the individual thinking about various ideas and
their ramifications, and NOT by just explaining it.

As to careful explanations, there is research that shows students learn less
from careful explanations than from explanations that have some confusion.
The confusion forces them to think it through themselves and thereby
understand better. Of course interactive engagement works even better than
either type of explanation. I assume the intended recipient of my message
will either not get it, or not respond, because of non-interaction.

John M. Clement
Houston, TX



Then: If you start talking to students about "interactions"
there is zero chance that they will understand what you mean.
It's a physics jargon term that is simultaneously highly
technical and rather nebulous. If you're careful you can
explain how a local, short-range, indeed zero-range coupling
can give rise to a long-range net interaction.
However, it's going to take a lot of explaining before the
students have any clue what you're talking about.