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

["Bob Sciamanda" <treborsci@verizon.net>]

My point is that the motion of an observed mass in free fall is determined 
ONLY by the properties of the observer's frame.  In other (non free fall) 
situations, other influences will also affect the observed motion of the 
mass.  This is what motivates my suggestion to name your (1)g the "free fall 
g".

-----Original Message----- 
From: John Denker
Sent: Saturday, January 05, 2013 7:53 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] two very different "gravity" concepts

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.

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Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://mysite.verizon.net/res12merh/