The principle of buoyancy is called Archimedes's Principle, since it was discovered by this Greek mathematician in the third century B.C. The principle states that the buoyant force acting on an object placed in a fluid is equal to the weight of the fluid displaced by the object. An object completely immersed in a fluid (liquid or gas) displaces a volume of fluid exactly equal to the volume of the object. The weight of that volume of displaced fluid is the buoyant force acting on the object.

Fluids such as water or air exert pressure in all directions and the amount of pressure depends on the depth of the fluid. The pressure on the bottom of an object immersed in a fluid will be greater than the pressure on the top of the object. The imbalance of pressure acting on the object creates...