# What's the point/area of space called where there is equilibrium between 2+ different gravitational forces?

For some reason I want to call it a 'gravity well' but I know that a gravity well is just the gravitational force distribution in space due to an object with mass.

But regarding my question, isn't there some term that describes this 'sweet spot', like balancing on top of a ball, where the gravitational pull of both/all massive objects is equal, and therefore an object floating on the spot will have less of a tendency to drift about, unless, again much like being on top of a ball, it is perturbed slightly, causing a gradual pull in one direction.

I can't think of the word or description, but I know it must exist. It's hard to google something when you don't know what its called! Thanks in advance.

• are you thinking of Lagrange points?
– user20636
Jun 9, 2019 at 21:17
• @JCRM yes that's the one. Thank you. If you wanna write an answer I'll accept it Jun 9, 2019 at 21:33
• Lagrange points are not zeros or cancellation of gravitational forces. They are points where the forces result in stable circular orbits which are stationary in the rotating frame. They are zeros of the sum of gravitational forces plus the gradient of a pseudopotential in the rotating frame.
– uhoh
Jun 9, 2019 at 22:06
• At earth moon L1 point the earth's gravity is more than double that of the moon. At L2 and L3 the two bodies pull in the same direction. Gravity does not cancel at any of the 5 Lagrange points. Jan 23, 2020 at 13:39

The term you are looking for is most likely Lagrangian point. Often synonymous, but sometimes used less strictly is Libration point.

It's important to be careful about exactly what we mean when we say "cancels out", "equilibrium" or "static".

When we have more than one body, they can't all be static. If they didn't move relatively to each other, their mutual gravity would soon make sure they do.

Instead, in a three-body system, what we usually look for is maintaining the same relative distance to both the parent bodies. This means orbiting the barycentre at the same angular velocity as the parent bodies.

Said in another way, it's the gravity of both bodies, in addition to centrifugal force in the rotating frame of reference that together are in balance in some sort of tug of war game.

This can only happen in 5 distinct points:

They are commonly denoted with the numbers above, L1, L2 and L3 on the same line as the parent bodies, and L4 and L5 60 degrees before and after (those two also happen to be stable). It's also common terminology to use abbreviations of the parent bodies' names to identify them, so "EML1" refers to the Earth-Moon L1 point.

There are no common cases of such points with more than two parent bodies involved, except for some exotic ones

Also of interest is that inside a uniform shell of mass, gravity in all directions cancel out (the shell theorem)

• I believe Lagrange points is the term OP was looking for. But Earth's gravity is more than double the moon's gravity at the Earth Moon L1. Gravity doesn't cancel out at any of the Lagrange points. Add in the clarification that it's a tug of war between 3 players and you'll get my upvote. hopsblog-hop.blogspot.com/2016/11/… Jan 23, 2020 at 13:35
• In other words, the equilibrium point moves, and in fact accelerates due to its circular motion. The L1 point is a nearby point with very similar motion, but which is located far enough in the right direction from the equilibrium point that gravitation provides the acceleration needed for an object to stay at the point. The actual equilibrium point has no special name that I'm aware of, the Lagrangian points are of more interest. Jan 25, 2020 at 13:39