Archimedes's principle states that an object immersed in a liquid will be supported by a pressure equal to the weight of the liquid displaced by the object. This is caused by an equilibrium of forces. The two forces seeking equilibrium are gravity and pressure from the surrounding liquid. Gravity pulls the object down through the liquid. The pressure of the surrounding liquid is resisting the free fall of the immersed object. The degree to which the weight of the object corresponds to the weight of the displaced liquid determines whether the object sinks quickly or slowly or floats. The intensity of the pressure is in direct relationship to the depth.

A cubic foot of water weighs 62.4 lb (28.3 kg). Therefore, if an object placed in water has a volume of a cubic foot and weighs more than 62.4 lb, it will sink. Rocks sink because most rocks have...