Buoyant Force Buoyant Force A completely submerged body displaces a volume of liquid equal to its own volume. Archimedes' Buoyancy Principle asserts that an object immersed in a liquid will be lighter by an amount equal to the weight of the fluid it displaces. The upward force exerted by the fluid is known as buoyant force.
Buoyant force is caused by gravity acting on the fluid.
It has its origin in the pressure difference occurring between the top and bottom of the immersed object, a difference that always exists when pressure varies with depth. Imaging without the object, the same immersed space will be occupied by the same volume of fluid. The weight of those fluid is supported by other parts of the fluid. So the buoyant force is the weight of the displaced fluid. I hope this java applet will help you learn more about buoyancy.