Re: F=ma

[Gary Karshner <karshner@STMARYTX.EDU>]

Leigh,
        Sorry no good references, but Newton purposely built this ambiguity into
his physics. His third law tells us that action and reaction are equal or
interchangeable. Which is the action and the reaction?
        More importantly the Principia not only was designed to bury Aristotelian
Physics but Cartesian physics as well. The Cartesian's started with
mechanisms and then built their physics around it. For example, they
imagined gravity as the flow of ether into the vortex of the sun.
Centrifugal force was then necessary to keep the planets in orbit. Newton
pointed out that if this model was true that the planets should quickly
spiral into the sun as the leading side of the planet was colliding with
the ether and should slow down it motion. He invented centripetal
acceleration as an answer to their force.
        The Cartesians criticized Newton's work for not telling us what gravity is
but only how it behaves. Newton responded that all you need to know is how
it behaves. This tension, of course, is still with us as any follower of
this list will attest. Newton avoided causes in part because it had lead
the Cartesians so badly stray.
        Just a few in sites into the causes of your wondering.

Gary

At 07:02 AM 11/5/99 -0800, you wrote:
> I've always looked at Newton's second law as being somehow incomplete.
> It does not include what I consider to be a causal element. Forces do
> cause accelerations, at least that is what my intuition tells me, or I
> was successfully brainwashed a long time ago. (This latter possibility
> is often referred to as "common sense".) Newton's law, especially
> written with a "coefficient of inertia", the mass, does not imply that
> forces cause acceleration. If one were to write it as a=HF, where
> H=1/m is the coefficient of compliance (or some other such name) it
> would look better to me.
>
> Someone clever must have written about this. Anyone out there know a
> favorite read on the topic?
>
> Leigh
Gary Karshner

St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU