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Re: F=ma



At 07:02 AM 11/5/99 -0800, Leigh Palmer 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.

Leigh raises an interesting (indeed profound) question.

Here is a good way of resolving the question: F does not cause ma, nor
does ma cause F. The laws of physics (and equations in general) do not
express "causation" as the term is usually understood. It suffices to say
that you can't have F without ma, and vice versa.

Causation is directional. Equivalence, according to the formal definition
of equivalence, is nondirectional (reflexive). F is equivalent to ma.

Someone clever must have written about this. Anyone out there know a
favorite read on the topic?

Richard Feynman, _The Character of Physical Law_. I strongly recommend
reading the whole book.... but the passage that most directly addresses
Leigh's question starts at the top of page 46.

______________________________________________________________
copyright (C) 1999 John S. Denker jsd@monmouth.com