Re: F=m*a before kinematics?

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

Peter Schoch wrote:

> We used to do this [F=m*a before too many kinematics
> problems] at Lehigh, when we used the book by Radin
> & Folk.  It worked excellently!  ....If I could find a
> book to do it this way now, I'd jump at it! ....

I will try to teach this way. In my textbook F=m*a is after
chapters on kinematics but I can introduce it earlier and use
it as a guide for deciding about the direction of acceleration.
The nuances of Newton's laws will wait till kinematics is
done but the idea of "net forces cause accelerations" will
be introduce together with the concept of acceleration.

The acceleration sign rule is going to be simple. In a chosen
coordinate system a component of "a" is positive when the
direction of the net force component is along the positive
axis. And it is negative otherwise. In a vertical case (with
y axis up) the acceleration "a" must be negative, even when
the speed is increasing. I suppose that most textbooks can
be used to implement this approach.
Ludwik Kowalski