Formula
Pressure is the force applied per unit area: p = F / S.
ENT-level problem
Find the buoyant force acting on a steel ball of volume $V = 0.001$ m³ that is fully submerged in water. The density of water is $\rho = 1000$ kg/m³, $g = 10$ m/s².
By Archimedes' law the buoyant force equals the weight of the water displaced by the body:
$$F = \rho g V = 1000 \cdot 10 \cdot 0.001 = 10 \text{ N}$$
Pressure shows how much force acts on a unit of area. In SI it is measured in pascals: 1 Pa = 1 N/m².
In practice atmospheres (1 atm ≈ 100 000 Pa) and millimetres of mercury are also used. Pressure grows either through more force or through less area: the same 100 N on a high heel gives a much larger pressure than on the whole foot.
In pascals (Pa): 1 Pa = 1 N/m². Non-SI: 1 atm ≈ 100 000 Pa ≈ 760 mmHg.
Multiply the pressure by the area: F = p · S. For p = 5000 Pa and S = 0.02 m² the force is 100 N.
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