Re: [Phys-L] two very different "gravity" concepts

[John Denker <jsd@av8n.com>]

On 01/05/2013 05:17 PM, Bob Sciamanda wrote:
> OK, but one measures the "g" of a given frame by observing, from that frame, 
> the motion of a mass in "free fall".  No?

We agree that the "drop" method is one way of doing it.
It makes a fine Gedankenexperiment.
It also is used in practice, by top-notch experts:
  http://www.microglacoste.com/pdf/newgeneration.pdf

Meanwhile, there are other methods that also work.  Weighing
a known mass works just fine for a wide range of practical 
purposes.
  http://www.aircraftspruce.com/menus/in/accelerometers.html

The fundamental physics point remains that the same "g" acts
on all objects, whether they are freely falling or not.

This g fundamentally reflects the absolute acceleration of 
the /frame/ rather than the acceleration of any particular
object.  The g field exists even in regions where there
are no objects at all.