Why does the liquid press on a submerged body from the bottom up?

The liquid presses on the submerged body from all sides normal to the surface.

For clarity, consider a submerged cube with side a.

The forces with which the liquid presses on the side faces balance each other.

Top and bottom pressures:

Pv = ρgh,

Pн = ρg (h + a),

where ρ is the density of the liquid,

g – acceleration of gravity,

h is the immersion depth of the upper face.

The force Fв = PвS = ρgha ^ 2 (down) acts on the upper face, and Fн = PнS = ρg (h + a) a ^ 2 (up) on the lower side.

Result: the buoyant force is directed upwards F = Fн – Fв = ρg (h + a) a ^ 2 – ρgha ^ 2 = ρga ^ 3 = ρgV (V is the volume of the cube).