Re: summary of weight

[John Denker <jsd@MONMOUTH.COM>]

At 07:26 PM 10/16/99 -0400, Bob Sciamanda wrote:
> > . . .
> > Arguably an even better way to do it would be to imagine super-tall
> > scaffolding on rails, moving westward relative to the earth's surface so
> > as to nullify the earth's rotation.
>
> It would seem that this would subtract coriolis and centrifugal inertial
> effects from your g value.  Are not these effects part of the chosen
> frame?

It depends on what you mean by "the" chosen frame.  One of the main themes
here is the existence of a multiplicity of inequivalent frames that might
reasonably be chosen.

If you choose to sit in the lab watching a centrifuge, centrifugal effects
are not part of your g value.  If you choose to ride in the centrifuge,
using the centrifuge cabin as your frame of reference, then centrifugal
effects must be included in your g value.

You are free to chose:
 a) a nonrotating frame comoving with the center of the earth, or
 b) a frame comoving and corotating with the earth, or
 c) something else entirely.

Choose what you like -- but remember that choices have consequences.  For
locations at or near the earth's surface, the effect of the earth's
rotation is pretty small, so (b) is a common and sensible choice.  OTOH
when you go out to astronomical distances, the consequences of choice (b)
get pretty messy.

Most students don't have the mathematical sophistication to handle rotating
reference frames reliably, so for analysis of orbits etc. I would nudge
them toward option (a).

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