Re: [FT] Help: Planets and Gravity

>	I'm glad there's a discussion going on about this right now
(though
>I haven't been keeping up with it. It enables me to ask a question for
a
>scenario I've been thinking of building. I want to set a battle around
a
>pair of Roche worlds. They're a pair of giants ~20 MU diameter,
semi-gas
>planets. They co-orbit a center point with about 4 MU of space between
them.
>htey probably need to be distorted egg shapes. The pair rotate a clock
>facing every turn.

OK, but remember, you asked for it!

I actually kind of question if that particular configuration would be
stable (they seem awfully close), but let's roll with it...

We'll kick things off with the Universal Law of Gravitation:
F=(G*M*m)/(r^2)

...where G=6.67*10^(-11) Nm^2/kg^2, M and m are the masses of the two
bodies, and r is the distance between their centers of mass.

That'll help figure if your rotation is right. I don't know what you're
using for an MU.

The acceleration caused by each body will be: a=(G*M)/r^2

...where G is as above, M is the mass of your planet, and r is any given
distance from the surface.

It will help for you to draw a picture of each gravitational field to
get
an idea on how they interact. On the exact line between the planets,
there
will be no gravity, as the two vectors will cancel out. The field will
grow
to the planet's normal value at about 60-70 degrees off the line
connecting
the two, and then increase to a maximum on the far side of each.

>	1) I want an atmosphere in the space between them - the main
>habitable part of the system.

Doesn't affect the gravity equations (much).

If you need more info, ask.

Schoon