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Re: F=ma



At 01:45 -0800 11/10/99, Miguel A. Santos wrote:
On Tue, 9 Nov 1999, Leigh Palmer wrote:

I recognize that what I've said above applies also to Newton's
second law when it is applied to forces of contact. There is a
possibility of a causal element when Newton's law is applied to
forces that act at a distance, however.

But not within Newtonian mechanichs, isn't it?
Could you explain a bit more what you mean in this last sentence?
I suppose you're thinking in terms of an interaction which travels with
finite velocity. But for Newton, altough he admitted no to be comfortable
with it, the forces acted intstantly. It would seem that not even for
forces acting at a distance could you mantain then your 'causal element'.

Yes, that's what I had in mind. While the Natural speed limit was
not part of Newton's phyics, it is somehow part of the package that
comes to us as a beginning student. It is in the popular culture,
even if it got there by nefarious (non-physics teaching) means.

Well, I'm a physicist and I got time to learn this point, but what about
the three-years ingeneers studies? Here in Spain, they all have an almost
common physics course during his first semester. Should one also care
about how to state things like F=ma? Is it worth enough, I mean, does this
care improves really their understanding?
What about at High School? Is this refinement really effective or can it
be subtituted by letting them do enough exercises, discussion,...?

I recognize no fundamental differences among groups of students
classified by discipline*. There are probably larger differences in
classifying them by sex, and those differences are not great. The
recognition of a much greater diversity of ability to assimilate
new concepts within any particular group is one I have to keep
reminding myself of repeatedly.

Leigh

*Our engineers are better physics students than our physics majors,
but they were more rigorously selected on entrance; they were all
straight A students in high school. The difference has nothing to
do with engineering *per se*. Engineers always make up the largest
group of students in my (elective) junior astrophysics course.