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[Phys-L] Re: Aristotelian thinking among modern students



1) I hope that somebody planing to write a really innovating
Introductory Physics textbook pays attention to some of our threads.
Most textbooks are essentially similar because authors (and publishers)
do not want to take a chance. On the other hand, a really innovating
text is needed. An author and publisher willing to take a chance might
be able to produce something that is not only useful but profitable as
well.

2) I am puzzled by the "Slo" in your signature file John. It wasn't
there last year. What does it represent?

Ludwik Kowalski
Let the perfect not be the enemy of the good.


On Oct 20, 2005, at 1:55 PM, John Mallinckrodt wrote:

I can understand students' misunderstanding with regard to velocity
being zero and acceleration not being zero, but I am amazed that
students would think that some force other than gravity was acting
on the object to make it move upward, even after it left the hand
that threw it. It very much reminded me of Aristotelian thinking.
Any comments?

This is just one reason why, IMO, the impulse = change in momentum
approach to Newton's second law is SO much to be preferred to the
acceleration = net force/mass approach. [Another is the fact that
you can delay even mentioning the word acceleration until much later
in the course. As I've mentioned before here, the concept of
acceleration is one that I believe even Newton himself had difficulty
with. Moreover, Newton actually uses the word "force" in place of
what we call "impulse." See
<http://lists.nau.edu/cgi-bin/wa?A2=ind0204&L=phys-l&P=R4205&m=18041>]

Call it Aristotelian thinking if you like, but I think Newton himself
had something pretty similar in mind. The reason students think
there is something other than gravity that has an influence on the
motion of the rock is because there is--the hand that threw it. They
don't see any good reason to deny the influence of the hand just
because it is no longer in contact with the rock and it is obvious to
them that, absent the influence of the hand, the rock would not be
going up.

The hand does "give something" to the rock that the rock now "has",
not force, of course (of course, of course. No one can point to a
force of course! (Sorry, just my sixties childhood getting the better
of me once again.)) but momentum. At this point in the course they
haven't been told about impulse and momentum, but I would submit that
they understand the CONCEPTS of impulse and momentum intuitively (as
Newton did) much better than they do what we call "force." It only
makes sense to capitalize on the correct ideas they have and refine
them rather than try to beat those ideas out of their heads and
replace them with less intuitive notions.

--
John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>