Re: Newton's first law

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

Glenn Knapp wrote:

> I don't know, the first law seems to go down well with my
> students, it's the old third law that they have trouble with.

This is probably because "F, m and a" are  introduced as
physical quantities before trying to establish a relation
between them. As I already indicated, this is acceptable
in an introductory course, at least at our university. First
we learn about kinematics and show how an acceleration
can be determined. Then we show how to measure m
(with a scale) and F (with a spring). In that context all
three laws are generalizations of experimental facts.

Conceptual difficulties, as emphasized by several people
on this thread, occur when we try to turn physics into
an axiomatic science (mathematics). This is a highly
challenging and worth pursuing approach for a more
advanced course. An axiomatic approach calls for an
acceptance (justification ?) of axioms and that is why
the first law seems to be so difficult. It becomes the
chicken-and-egg dilemma.

Keep in mind, however, that I have no experience in
teaching an advanced mechanics course. This comment
is only a guess, based by long forgotten frustrations.
Ludwik Kowalski