# Archimedes' principle and pressure It says that the medium is water. I know from Archimedes' principle that we can calculate the buoyancy force by calculating the hydrostatic pressure on the top of the object and below the object, and subtract the forces resulting in the buoyancy force.

However, why does this work? As far as I know, the hydrostatic pressure depends on depth ($$p=ρ*g*h$$) because there are water layers on top of each other which increase the pressure with depth. However,under the cube (where it says 2943 Pa) there is no water above it, but we can still calculate the water hydrostatic pressure like we're used to. Why?

• Interesting that the English version of the Wikipedia article doesn’t have this figure. It should also be noted that the pressures shown are guage, not absolute Aug 28 at 9:22

Pressure is a scalar quantity and so the pressure immediately below the cube is $$2943\,\rm Pa$$ at every point along the bottom of the cube and along a horizontal line extending to the right and left of the base of the cube.
Given that the pressure immediately below the cube is $$2943\,\rm Pa$$, the water exerts an upward (normal} force equal to $$2943 \,A\,\rm N$$ on the base of the cube where $$A$$ is the base area of the cube.