Re: Student Questions

["John S. Denker" <jsd@MONMOUTH.COM>]

Tina wrote:

> > I am currently teaching forces to my general physics
> > class.

John Barrer wrote:
> Start by getting them used to the question "What
> objects are interacting with the mass?"

If that means what I think it means, then I'm not
convinced that's the right starting point.

I don't subscribe to the school of thought that starts
with position -> velocity -> acceleration and then
_defines_ force in terms of F=ma.  (If force is defined
that way then F=ma becomes a tautology.)

Instead, I take the point of view (both for physics
reasons and pedagogical reasons) that force exists
unto itself.  (Therefore F=ma is a nontrivial
expression, subject to experimental verification
or falsification.)

Specifically, I would hand the student one end of a
rope.  I pull on the other end and say
        "Feel that?  That's a force."
I pull harder and say
        "Feel that?  That's a larger magnitude of force."
I pull off to the side and say
        "Feel that?  That's a force in a different direction."

You will note that these exemplary forces are defined
absolutely without reference to any mass.