If you have tried to push a beach ball under the water you have experienced how the
water pushes back with a strong upward force. This upward force is called the buoyant
force , and all fluids apply such a force to objects that are immersed in them. The
buoyant force exists because fluid pressure is larger at greater depths.
An object immersed in water generates a downward force ,
where is the area of its top surface. The object
also generates an upward force , where
is the area of its bottom surface. (For clarity,
the object has same top and bottom areas.)
In conclusion, any fluid applies a buoyant force to an object that is partially or
completely immersed in it ; the magnitude of the buoyant force equals the weight of the
fluid that the object displaces. This is called the Archimedes' Principle and it is
written in an equation :
2. Weight of the displaced fluid.