Re: multi-step reasoning

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

I may be dense this morning, but it seems to me that changing the volume
by definition means that work will be done...so I don't know what it
means to say "if no work is done"
If I think of a PV diagram, then even for constant n, it is clear that
there is an infinite numbers of paths which will double the volume of
the ideal gas.  This is of course not obvious if the students think only
in terms of the equation...hence the value of the graphical
representation.

joe

On Wed, 21 Aug 2002, Chris Horton wrote:

> If no work is done then t can't change - something which is extrinsic to the
> equation.  There is the rub.  You have to specify how this could happen.
>
> So if t doubles what happens to P and V?  Answer me that!  Hah!
>
> 8-)
>
>
>
>
> > From: Herbert H Gottlieb <herbgottlieb@JUNO.COM>
> > Reply-To: "phys-l@lists.nau.edu: Forum for Physics Educators"
> > <PHYS-L@lists.nau.edu>
> > To: PHYS-L@lists.nau.edu
> > Subject: Re: multi-step reasoning
> > Date: Wed, 21 Aug 2002 01:28:32 -0700
> >
> > Chris...
> >
> > I was quite interested in your PV question below and
> > wondered if I was able to arrive at the correct answer myself..
> > I reasoned that if V is doubled, (other things being equal)
> > then P would immediately be reduced to half its value and the
> > nRt would remain the same.
> >
> > Is my reasoning correct???
> >
> > Herb
> >
> > On Wed, 21 Aug 2002 00:39:41 -0300 Chris Horton
> > <chrisahorton2@HOTMAIL.COM> writes:
> > > One place where students are called on to think beyond a simple
> > > relationship
> > > is with the ideal gas law
> > >
> > > PV = nRt
> > >
> > > I don't have my sources available but I was reading recently how
> > > nearly all
> > > students - including some graduate students in chemistry - faced
> > > with a
> > > question like "what will happen if V is doubled?" will either ignore
> > > one of
> > > the three variables, or apply them one step at a time in a
> > > sequential
> > > reaoning process, usually imagining a two-step process over time.
> > >
> > > What is going on is that they are trying to arrive at an answer
> > > algorithmically, when the algorithms won't give them a meaningful
> > > answer.
> > > What is needed is to have the students learn to habitually create
> > > models of
> > > situations, and consider carefully what all the constraints are on
> > > their
> > > models, before trying to crank out an answer.
> > >
> > > Students can learn this habit but they won't as a rule come up with
> > > it
> > > themselves.  Students want the easy way and that ain't it! But once
> > > they
> > > learn it they will find it is not just a more powerful way, it's
> > > also more
> > > satisfying.
> > >
> > > 8-)
> > >
> > > Chris Horton
> > >
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>
>
>
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Joseph J. Bellina, Jr.               574-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556