Archimedes' principle states that any body completely or partially submerged in a fluid at rest experiences an upward, or buoyant, force equal to the weight of the fluid it displaces. This physical law of buoyancy was discovered by the ancient Greek mathematician Archimedes, supposedly while he was taking a bath.
Archimedes' principle has several applications, one of which is to determine density and specific gravity. The principle also explains why objects float. If the weight of displaced liquid equals the weight of an object, it floats. If the displaced liquid weighs less than the object, the object sinks. When an object weighs less than the fluid it displaces, such as a helium-filled balloon, it rises.
The buoyancy principle, named after the Greek scientist Archimedes, is a law of physics critical to the design of ships. It allows the volume of an object to be calculated by the volume measurement of fluid displaced after submerging the object.
When the displaced fluid weight equals the weight of an object submerged, the object floats. This is why a steel ship floats on the sea. If the weight of an object is less than the weight of the displaced fluid, such as a submerged ball, the buoyancy force equal to the weight of the displaced fluid will exert an upward force upon the object.