Re: operational F, m, and a

["Carl E. Mungan" <mungan@USNA.EDU>]

Joel wrote:

> I still think there is an implicit acceleration measurement occuring,
> however.  Remember we are dealing with Newton's second law, which I will
> paraphrase as:
>
> In an inertial frame of reference, the sum of the forces acting on an object
> is equal to the objects mass times its acceleration.
>
> That means, in order to use the fish scale to determine force in the context
> of Newton's second law I have to make sure that the tick mark scale on the
> apparatus is a good inertial frame of reference, which means I must
> implicitly make another kinematic measurement, namely that the tick mark
> scale has zero acceleration relative to some fiducial inertial frame of
> reference.
>
> If you buy this, it means that equilibrium measurement determinations of
> force involve measurement of acceleration.

Can't we use Newton's first law (N1) to decide if a reference frame
is inertial?

Specifically, find an object which is isolated (ie, in deep space -
this is a Gedanken experiment). Now look to see whether the object is
accelerating relative to your reference frame.

Thus, I take N1 to be a definition (namely of an inertial frame).
With this definition, I now take N2 as an experimental law, in accord
with John D's prescription.
--
Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
      U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu    http://physics.usna.edu/physics/faculty/mungan/