The Archimedes Principle (called the law of buoyancy), states any vessel partially or totally submerged in a fluid has an upward force acting upon it that is equal in magnitude to the weight of the fluid displaced by the vessel. The volume of the displaced fluid also equals the volume of the submerged portion of the vessel.
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.