Archimedes' principle When a body is partially or fully immersed in a liquid, it experiences an upward thrust which is equal to the weight of the fluid displaced by the body. Therefore the weight of the body immersed in a liquid is reduced. The reduction is equal to the weight of the fluid displaced. A floating body displaces its own weight of fluid. The upward thrust, is called buoyancy. This force acts through the centre of gravity of that fluid which would replace the immersed part of the body.