Fluid dynamics, sometimes referred to as fluid mechanics, is the study of fluids at rest or in motion. Biologists define a fluid as a water-based liquid that contains and transports the fundamental fundamental elements vital to life, but physicists, taking a broader view, define a fluid as any substance which flows under pressure. Essentially then, matter is either solid or fluid, with two basic types of fluids: gasses, which expand to fill the container or volume they are in, and liquids, which settle to the bottom of their container.

Over a wide range of situations gasses and liquids flow in similar fashions and can be described by the same equations. Some examples are flow through a pipe, flow around a body such as a rock in a stream, and flow due to temperature differences. Such cases arise in a wide variety of fields, such as aeronautical...