Re: equal gravity

[Leigh Palmer <palmer@SFU.CA>]

> There is no "ridge of equal gravity".  As 1.) shows, there is only a
> single "zero-gravity" point.  I think you have mis-remembered the article
> content.  It does not jog anything in my memory :)

He may be (mistakenly) thinking about the Roche lobe in the restricted three
body problem. That's where the "massless" particle is seen; it is one of the
"restrictions". It is also a rotating frame in which the centrifugal force
also acts, and in which there are four more "weightless" (if not zero
gravity) points*. As Bob Sciamanda pointed out, however, there is no ridge on
which a particle can rest and remain weightless. It is difficult to imagine a
physically interesting situation involving two gravitating masses in which
there is no rotation (two masses attached to a massless rigid stick?). Now a
continuous mass distribution is another story, and the current maneuvering of
the NEAR spacecraft is very interesting to consider because the asteroid it
is in orbit about, Eros, is far from being spherical.

Leigh

*Two of these points are points of stable static equilibrium, not a violation
of Earnshaw's theorem because a centrifugal force is involved here.