Archimedes Principle

Archimedes' Principle, in Hydrostatics, the principle that a fluid exerts a resultant upward force on any body immersed in it, exactly equal to the weight of the fluid displaced by the body. If, therefore, the weight of the body be less than that of the fluid displaced, there will be a tendency for it to move upwards, as in the case of a balloon. If equal to the weight of fluid displaced, the body will remain at rest in any position within the fluid. But if greater, the body will tend to sink.