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[Phys-L] Re: A Third law question

Now as described it certainly sounds more reasonable. It conforms to what
we know about student learning. And it would certainly work better than
"conventional" education because it puts everything in a hands on, minds on
context. Note that the other reformed programs also do similar things, but
at a different starting point. For example most have the students actually
find the relationships involved such as a=F/m through an experimental
procedure.

Unfortunately, it is still necessary to find out what the ideas the students
actually come away with and the only tests that do this currently are the
FMCE/FCI. One could use some of the McDermott evaluations, but they are
generally not as comprehensive, and results based on them are not as well
published. The anecdotal evidence you cite is certainly favorable, but such
evidence can really only be supporting evidence. I have no doubt that your
program works better, but does it give 70% normalized gain? At present the
maximum gain has now been pushed to close to the 90% level by a few
Modelers.

The other question is which sequence works best with various levels of
students. I have the definite feeling that it will not work as well with
lower level students who lack proportional reasoning and are very weak in
conservation reasoning. The big advantage of going V -> a is that the idea
of the area under a curve has meaning for the V-t graph. Students actually
come up with the idea of adding up the area in strips. Once this idea has
been established for one model, it may be easier to use the area in other
contexts. The momentum first sequence may be better for formal operational
thinkers, or in the end it may actually produce the same results as the
"conventional" sequence implemented in a reformed fashion.

My real skepticism is that momentum first is "superior" or the best way. I
will grant that it can work better than traditional pedagogy if it is
implemented in a research based fashion, but not necessarily better than
other research based pedagogies. In the end it may be that it works equally
as well, or that it produces greater strengths in a complementary fashion to
the other reformed pedagogies. But we don't know because there are not
published results that can be compared to other researchers.

I would not hurt to give the FCI or FMCE as pre and posttests just to see
what results you get. You might just be surprised either pleasantly or
unpleasantly. Either result should be published to add to the growing data.
So far the only a few sequence changes have been verified as being better.
There is evidence that momentum should be taught before energy and that 1-D
examples should be exhausted before going on to 2-D examples. Beyond this
there is little evidence for other major sequence changes. The 1,2-D
problem has been confirmed by McDermott in the latest AJP and has been
previously reported by Laws et al.

John M. Clement
Houston, TX


> Let me reiterate what John D. said. Conservation of momentum is the
best way I know of to get students to understand forces and their
affects, including N3. It doesn't require fancy equipment to get
students to accept it, only a few demonstrations and some hands-on
work by the students. If these are gen-ed students, they really need
to get that hands-on work, so they will know what to do with their
> students in due course, and why.
>
And then,

At 19:06 -0500 10/12/05, John Clement wrote:

And what evidence is there for this assertion? Can you show this by pre
and
post-testing on either the FCI or FMCE? I truly doubt it.

Conservation of momentum is weakly connected to forces in the minds of
students. Indeed getting them to make the connection is fairly
difficult.
There are some excellent direct demonstrations of the effect of forces in
the Interactive Lecture Demonstrations by Thornton et al that work fairly
well and show high gain on the FMCE. Can you demonstrate similar gain by
using conservation of momentum labs?

If you can get similar gain then by all means publish the results so that
others can use the same method.

I don't have FCI or FMCE results to show for this since I don't use
either one (I am not yet convinced these test measure anything of
real value, but let's not get into that argument here), but I have
taught an intro course for the past 10 years in which we start with
momentum. The students establish the conservation of momentum
empirically, using air-track collisions. No use of the word force
happens until after the momentum section is completed, but once they
understand momentum, then examining the details of collisions allows
force to arise in a very natural manner as "what it is that causes
momentum to change." Once we have momentum as a concept and they have
more or less internalized it, it is quite possible to "derive" all
three of Newton's laws (we use a rather arm-waving technique, and
make no claims of rigor, either here or with the students), but it is
also made clear to the students that we could have started with
Newton and then "derived" the conservation of momentum. Only after
Newton's laws are in their hands to we delve at all deeply into the
nature of force, acceleration is also a late-comer to this program,
as are the kinematics equations.

My admittedly qualitative impressions, based on a comparison with
general student performance over the prior ten-year period is that
the students come away from this with a firmer grasp of classical
physics in general. They appreciate the conservation laws, and they
understand more about the nature of forces. Such feedback as I have
had from former students has generally been positive. They say that
the physics courses they had in college were easy for them, compared
to other students who had been exposed to physics in a more
traditional setting.

I would agree that, in a traditional setting, force and momentum
would likely be only weekly coupled, since they are typically taught
as essentially unrelated topics, so it isn't likely that most
students would see the connection in a first course. But if one
follows a pedagogically logical sequence, in which each new topic
follows naturally from the preceding ones, it is much easier for the
students to see the connections. I have had students complain about
why we even have them learn about forces, since momentum is a so much
easier way to solve the same problems. The idea that both force and
momentum could be used to solve many types of problems never occurred
to out students before we started doing momentum first.

Ruth Chabay and Bruce Sherwood are teaching engineering physics to
students at NC State using this method (momentum first), and that is
the format that their text, "Matter & Interactions" follows. Since
they are in a better position to conduct research, I suspect that
they may have the sort of data you requested. Why don't you ask them?

Our program was developed independently of them, but in my
conversations with them, they indicate their impressions to be much
the same as I have outlined above.

Hugh
--

Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

(919) 467-7610

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