Re: F=ma

[Leigh Palmer <palmer@SFU.CA>]

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.