Re: Apparent weight

["A. R. Marlow" <marlow@loyno.edu>]

On Sat, 21 Feb 1998, Rauber, Joel              Phys wrote:

> ...
> Put more simply, "how do I know if the frame of reference I'm using for 
> measurements is inertial?", I have to know this before (and independently) 
> to decide if a measured acceleration indicates a force that  passes your 
> acid test or not.
>
> I can certainly say, my frame of reference is inertial with respect to the 
> star frame (let's rather say the far away galaxy frame); but that doesn't 
> resolve the question, as I don't know if the far away galaxy frame is truly 
> inertial or not.
>  
> It strikes me that Bowman's attitude towards forces makes the need for this 
> knowledge moot.
>
> Joel Rauber

Thanks very much for the 1958 reference to AJP;  I haven't read that paper
in some years, and had lost the reference.  I will certainly look it up
again and reread it.

I think that Doppler variations in the universal microwave background are
nowadays used to try to determine whether or not you have an inertial
reference frame, as well as to give our speed relative to the average
galactic framework, but neither those or the galaxies are taken as the
definition of inertial frames.  The only definition I know is the one that
says "If there are no accelerations except those corresponding to the
measured physical forces present, then you have an inertial frame."  This,
of course, presumes that you have means of measuring forces as
primitive physical quantities in themselves ("pushes and
pulls")independent of detecting the very accelerations that the forces
produce.

As discussed in many previous posts, I have no problem with that, and
accept various pressure sensitive devices (as well as human tactile
sensation as an approximate guide over a limited region) as valid bases
for independent force measurements.

I think you are right in suspecting that the mathematical construct
approach toward forces makes the need for this moot, since in that
approach forces need not be tied to any such independent detection and
can be supplied by mathematics.  I'm not sure how that approach treats the
source tensor (containing such things as pressure density, Etc.) for
general relativistic curvature



A. R. Marlow                          E-MAIL:
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