Buoyancy
The net upward fluid force exerted on an object immersed in a fluid due to pressure difference between top and bottom.
Governing formula
Fb = ρ_fluid V_submerged g
SI unit
N
In depth
Fluid pressure increases with depth. Higher pressure at the bottom exerts a net upward force equal to the weight of displaced fluid.
Examples in the real world
A massive steel cargo ship floating because its hollow hull displaces a volume of water weighing more than the ship.