In a static fluid an important property is the pressure in the fluid. Pressure is familiar as a surface force exerted by a fluid against the walls of its container. Also, pressure exists at any point in a volume of a fluid.
In order to understand pressure, which is defined as force exerted per unit area, we must first discuss a basic law of Newton's. This equation for calculation of the force exerted by a mass under the influence of gravity is
where in SI units F is the force exerted in newtons N (kg · m/s2), m the mass in kg, and g the standard acceleration of gravity, 9.80665 ...