It's a theoretical study. I would like to understand how the sum of forces can be at 0 if I put an object (vacuum in it) in a big liquid disk (disk is fulled with liquid), the disk is big enough for agglomerate liquid (like this works with a planet, matter is agglomarate with gravity). There is no external circular wall for disk ! it's very important. I attach the vacuum object with something external at disk (black color). The vacuum object has an extenral force give by liquid, force of buoyancy, this force is transmited to black object. I study the sum of forces on all the system (vacuum object+disk+black object). What's compensate this force ? How liquid can compensate this force ? And if liquid compensate the force, this would say if I put a bubble in water the bubble go to one direction and water go to the contrary direction, this would change the center of gravity.