When an object is placed in water, the water provides it with an upward force . This is called UP-THRUST. Up-thrust is the force that pushes an object up and makes it seem to lose weight in a fluid. The up-thrust force acts on a heavy material.It helps to cancel some weight of the material and helps the material weigh less in water than in air. If we weigh the weight of the placed material in water, the displaced water is equal to the up-thrust. This principle is known as ARCHIMEDES PRINCIPLE.
If the immersed material in water weighs greater than its up-thrust, the material will sink in the water. The object can only float when the up-thrust equals the weight of the object. For example the boat is able to float in water because its weight is equal to the up-thrust. We are able to swim because of the upthrust as our weight equals it.