Re: is free-fall an inertial frame?

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

> > > is free-fall an inertial frame?
> >
> > Yes, no, and maybe.
If two reference frames are moving relative to one another with a constant
velocity, and one of them is an inertial reference frame, then the other is
also. I don't think anyone has a problem with this. If, however, the
relative motion between the two is not constant then both of them cannot be
IRFs. In the case of ref. frames attached to the earth and free-falling
near the surface of the earth, it would appear that one can choose which is
to be considered the IRF arbitrarily (that is, depending on which world
picture--Newtonian or GR--one desires to adopt), but whichever one we
choose as the IRF, then clearly the other one cannot be, as seen from the
chosen IRF.

This seems to be a bit of a paradox, and I may be painting myself into a
corner, but I guess it won't be the first time. A person in an earth-bound
laboratory can conduct experiments that (within the limits imposed by
rotation and variation of g) will obey F=ma, and can thus conclude that she
is in an IRF (approximately). She can then go to her neighborhood theme
park and conduct the same experiments in the free-fall ride and draw the
same conclusion (again, approximately). Her transition from one IRF to the
other occurs at the beginning and end of the ride when her acceleration
changes rather suddenly (jerk). But while she is falling, if she were able
to observe her alter ego conducting the lab experiments, she would assert
that, from her perspective, they did not satisfy F=ma (unless some
non-inertial extra force is postulated). The converse is also true. While
standing in the lab, the experiments conducted in the free fall ride will
also not satisfy F=ma (unless some non-inertial force--in this case
Newtonian gravity--is postulated to exist in the free fall ref. frame). Go
figure.

I'm getting dizzy, and it's not the Earth's rotation that is doing it.

Hugh

********************************************************************************
Hugh Haskell

<mailto://haskell@odie.ncssm.edu>
<mailto://hhaskell@mindspring.com>

The box said "Requires Windows 95 or better." So I bought a Macintosh.
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