define archimedis principle

"MAGNITUDE OF BUOYANCE FORCE IS EQUAL TO THE WEIGHT OF THE FLUID DISPLACED BY THE BODY."

Archimedes` principle, principle that states that a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid. The principle applies to both floating and submerged bodies and to all fluids, i.e., liquids and gases. It explains not only the buoyancy of ships and other vessels in water but also the rise of a balloon in the air and the apparent loss of weight of objects underwater.