Buoyancy is the term used to describe an upward force which acts upon an object, produced by the surrounding fluid. This fluid can be rather a liquid or a gas.
Pressure in a liquid increases with depth. Archimedes' principle states that an object fully or partly immersed in a liquid is buoyed upward by a force equal to the weight of the liquid displaced by that object.
This law helps explain how boats which weigh many thousands of tonnes can float on water.
The hydrostatic pressure at a depth h in a fluid is given by:
P = ρhg
ρ = the density of the fluid
h = is the depth of the fluid
g = standard gravity