Archimedes' Principle

A physical principle stating that a body wholly or partially immersed in a fluid at rest experiences an upward buoyant force equal in magnitude to the weight of the fluid displaced by that body.

A body wholly or partly submerged in a fluid at rest experiences an upward buoyant force whose magnitude equals the weight of the fluid displaced by the submerged portion; the resultant buoyant force acts through the center of buoyancy (the centroid of the displaced volume).