Re: Appropriate for Gen Phys? was: comprehending electric/magnetic interactions

[Jack Uretsky <jlu@HEP.ANL.GOV>]

        I guess my question is (try to forgive the loaded language), why
force a formal model on kids <at that level>.  The fun of science is
wading through all the wrong models. That's some of what we're trying to
convey, right?  And with that comment, I'll engage in a diversion on a
related subject that I just happen to be reading about.  Enter the
Y-Chromosome.
        A recent enjoyable, amusing, (and a bit ribald) book that got a
rave review in Nature, is <Y: The Descent of Men> by Steve Jones.  Jones
is an evolutionary biologist and a noted authority on Darwin, as you might
guess from the title.
        The theme of the book is the evolutionary self-destruction of the
Y-chromosome stemming from the fact that there is only one in the male
(note that I am not specifying species).  This leads to the well-known
prediction that the human male will become extinct in about 10 Myears,
simply as a result of reproductive errors.  That is, there is no second Y
that can serve as a model for correction of an error.
        The female line, by contrast, is much stronger because the X's
descend in pairs, enabling the correction of errors in the reproductive
process.
        In the last couple of weeks, however, the prediction of the end of
maleness has changed radically, and it appears that we've all swallowed
the wrong model.  Analysis of the Y-genome has discovered that DNA,
previously thought to be "junk", turns out to be duplicates of "real" DNA
needed for reproduction.  In other words, the Y can correct reproductive
defects using internal models, rather than an external model like the X
does.
        So in the year 2003 we can sing: Hallelujah, mankind (emphasis on
the "man" syllable) is saved!  This is part of what I think to be the
excitement of science.

On Thu, 3 Jul 2003, John Clement wrote:

> It certainly is a reasonable explanation, however the MOP series gives
> students a "formal model".  After exploration, the formal model is
> presented, and students are asked to reason using it.  Notice that this
> is a classic learning cycle.  They are then asked to distinguish between
> charges and "nanomagnets".  The domain structure is only touched on.
> The primary idea that students must work with is that macroscopic
> magnets consist of "nanomagnets" which are aligned for greatest
> strength.  They have already seen this effect in labs, and have seen
> that N and S poles are never separated.
>
> One of the things that is being demanded is that any statement they come
> up with must be consistent with all of the facts.  For example they see
> that bar magnets produce a stronger magnet by putting N to N & S to S.
> They also see that disk magnets are stronger when N & S are together on
> top of each other.  They have to give up simple N to N or N to S and
> instead think in terms of microscopic magnets or nanonmagnets lining up.
>
> They also have to realize that magnetic forces are NOT electrical forces
> and that different models apply.  With the beginning students this is
> very important.  A connection is made between them, but at this level
> they have to learn to distinguish between them.  Learning to reason with
> formal models is actually at the higher level of formal reasoning
> according to the Piagetian classification.
>
> At this point, many HS physics courses talk about electrical forces, but
> never really do anything with magnetic forces.  The misconception that
> magnets work by electrical forces is never properly addressed as a
> result.  Students still harbor the belief that magnets interact with any
> metal, and they never make the connection between compass needles, the
> earth, and magnets in the laboratory.  Incidentally magnets are often
> mentioned in history, but students usually do not make any reasonable
> connections there either.
>
> By the end of the combined electric, magnetic, gravitational unit many
> students are beginning to make distinctions, but sadly some are not.
> The "wrong" explanation is only "wrong" at the end, and is a perfectly
> good idea part way through.  I would also prefer to call a "wrong"
> explanation an inconsistent explanation with the model.  This actually
> mirrors the way science proceeds.  At any given stage "wrong"
> explanations are just explanations that are not consistent with current
> model or paradigm.
>
> John M. Clement
> Houston, TX
>
> >         Exactly!  What experiment demonstrates that the "dropping
> > the magnetic particles" explanation is wrong?  The entire philosopy
> that
> > most of us want to promote is "learning from experiment".  So there is
> a
> > level at which "particle dropping" is as good a hypothesis as any.
> >         In my experience it adds fun and interest to the classroom to
> > tentatively adopt primitive explanatios - the only proviso is that the
> > explanations must eventually be tested.
> >
> >
> >
> >
> > > Brian Whatcott    Altus OK

--
  "Don't push the river, it flows by itself"
                                Frederick Perls