State Archimedes principle.

Hint: Archimedes principle is based on the fact that the volume of the immersed object in liquid is equal to the volume of the displaced liquid. It basically tells us how the mass of the object in liquid is related to the amount of the displaced water. Hence we can define Archimedes principle for the above phenomenon.

Complete answer:
When immersed in water, the two surfaces that are the upper surface of the object and the lower surface of the object have two different forces. This is due to the fact that the pressure due to the column of water at a particular level increases with depth. Archimedes made an observation on how the up thrust generated on the body can be related to the water when the body is immersed in water.
Archimedes principle states that when a body is fully or partially immersed in fluid, it experiences an upward thrust equal to the weight of the displaced liquid and its upthrust acts through the centre of gravity of the displaced liquid.

Note:
To understand why the upthrust is generated consider the following example. Let us say we place a square block in the water of a particular height and say ‘h’. Now we know that the pressure due to the column of water increases with depth. As pressure increases, the thrust on the bottommost surface of the block will be greater than that of the upper surface. Therefore when an object is immersed in water, it experiences an upthrust. It is also to be noted that the up thrust generated is proportional to volume of the body immersed in liquid and not the entire volume of the body.