Archimedes' Principle:

While you take bath, you might have noticed that a mug filled with water and fully immersed in bucket of water does not feel as heavy as when it is taken out completely from the bucket. You could feel the raise in weight as the object comes out of the water. Do you know: why this is happen? This happens because of buoyancy. Buoyancy (an upward thrust) arises because the fluid pressure increases with depth. Because of this, there is an unbalanced upward force known as the buoyant force on the bottom of the object (like mug full of water) immersed in the liquid. The effect of buoyant force on objects immersed partially or fully in fluids is summarized in Archimedes' principle.

According to the Archimedes' principle, a body immersed in a fluid appears to loose weight and the apparent loss of weight is equal to the weight of the fluid displaced by it (the body). The apparent loss in weight of the body is caused by the upward thrust of the liquid on it, which is, buoyancy.