Buoyant force plays very important role to determine whether the object floats on the fluid or object sink inside the fluid.
Hydro-static pressure difference is the main cause of the buoyant force, due to increase in the pressure of the fluid with increase in depth cause an net upward push force on the object.
For floating object, the buoyant force acting on the object is equal to the weight of the object, and weight of the fluid displaced by the object is equal to the weight of the object.
An object floats if its average density is less than the fluid density (Buoyant force is greater than the weight of the object).
An object sinks if its average density is greater than the fluid density (Buoyant force is smaller than the weight of the object).
