ABSTRACT
The forces that exist within a fluid at any point may arise from various sources. These include gravity, or the "weight" of the fluid, an imposed static pressure from an external source, an external driving force such as a pump or compressor, and the internal resistance to relative motion between fluid elements, or inertial effects resulting from the local velocity and the mass flow rate of the fluid. A straightforward and most common application is seen in the everyday mercury barometer used to measure the atmospheric pressure. In its basic form, a glass tube filled with mercury is inverted so that its open end is well submerged in a mercury reservoir. As a consequence of Archimedes' principle, the buoyant force exerted on a submerged body is equal to the weight of the displaced fluid, and it acts in a direction opposite to the gravity vector.
