Re: [Phys-l] Equations (causal relationship)

["Edmiston, Mike" <edmiston@bluffton.edu>]

> Why don't we just agree as follows:
>   a) Sometimes ma is calculated from F and sometimes vice versa;
>   b) The equation F=ma covers both cases.

Absolutely.  I've never had a problem with that.

I can imagine a particle having its net acceleration resolved into a 3D
coordinate system.  I personally wouldn't say that a(x), a(y), and a(z)
are three simultaneous accelerations; rather, I would say they are
components of the one acceleration.  Then, when a(net) is zero, I would
say all the components are zero.

Where I have difficulty is imagining three simultaneous nonzero
accelerations that add to zero.  The only observable result is a(net)
equals zero.  I cannot oberve the individual nonzero accelerations.  I
don't think it is a failure of my imagination or my experimental skill
that I can't figure out a way to measure them, I think they cannot be
measured in principle.

So in my mind the question is, does the fact I can calculate these
accelerations from F=ma mean they exist even though it is not possible
to observe/measure them?

A more broad rephrasing of the question is, if we hypothesize something
exists, but then conclude it cannot be observed or measured, does it
really exist?  Of course with regard to this question I am familiar with
observables and non-observables in quantum mechanics.  However, the F=ma
case with macroscopic objects is not a situation with which I am
comfortable believing in non-observable realities.


Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu