Re: [Phys-l] definition of gravity

[John Mallinckrodt <ajm@csupomona.edu>]

On Nov 8, 2011, at 9:05 AM, John Denker wrote:

> On 11/08/2011 08:46 AM, LaMontagne, Bob wrote:
> > > What name do you give to that part of the" gravitational field"
> > > solely due to the presence of a nearby gravitating object (such as
> > > the Earth)?
>
> That is a seriously good question.  I've struggled with that.
> *) In many applications it makes sense to call it the /primary/
>  gravity (g_I).
> *) Sometimes I call it the /Newtonian/ contribution to the
>  gravity, in honor of Newton's law of universal gravitation,
>  and of his application of that law _in a nonrotating frame_
>  to the orbital dynamics of the moon.
>
> If anybody can come up with a cleverer name, that would be
> great!

In GR, the thing Newton calculates as GM/r^2 is simply the *relative* acceleration of inertial (i.e., freely-falling) frames located at 1) the center of a spherically symmetric object of mass M and 2) some distance r from the center and beyond the surface of the object.  It quantifies the effect of the spacetime curvature in between those two points.

John Mallinckrodt
Cal Poly Pomona