I would like study a theoretical problem. A system composed of 2 spheres can move at left of at right in water. One sphere has gas at low pressure and other sphere has water in it. The wall of spheres are very thin and has the same density of water. Sphere of gas don't has force because it has same water at left and at right. But sphere of water "see" a virtual sphere of water that attract it (because in other direction there is sphere of gas), this force is F1. The pressure must compensate F1 but I don't understand how because pressure is give all around sphere of water and density is not a linear law and angles are not the same (if you change angle, you change distance). And especially the layer around the sphere of water is not at R but at R more half thickness of molecule. Do you know if this calculation is done somewhere in the net ?