# I Gravity along ecliptic

1. Jan 11, 2017

### havonasun

I am curious to know if the gravitic field of a rotating, disk-shaped mass is denser along its ecliptic. I'm referring to rotating bodies such as stellar systems, galaxies, etc. I would like to know if a second mass, passing through the ecliptic, would experience a difference such as tidal forces or perturbations. Basically, does a massive disk have any difference in its gravitic pull axially vs radially? From a great distance, it would just be a point-source, but up close I'm thinking that the magnitude of the vectors of individual bodies comprising the whole would be less axially than radially.

2. Jan 11, 2017

### Staff: Mentor

The gravitational field of a disk is different from the field of a sphere. For a disk of uniform mass, this website has some plots of the gravitational potential. The force is orthogonal to the equipotential lines and stronger where the lines are denser.

3. Jan 12, 2017

### havonasun

From what I can interpret, the graph I would be using would be 'rotating w/star.' The field is densest at the center because of law of squares, and weakest horizontally from the center. It shows another dense region outside the disk radially. So, yes?

4. Jan 12, 2017

### Staff: Mentor

The page doesn't load right now, but as far as I remember the "rotating" probably included effective potentials for orbiting bodies. I'm not sure if you want that.

If the disk has a cylindrical symmetry, its rotation does not matter for the gravitational potential (ignoring relativistic effects).

Edit: Looks like relativistic effects are considered. Do you really want that?