Fundamental Concepts of Fluid Mechanics

Abstract

Matter is recognized in nature as solid, liquid or gas (or vapour). When it exists in a liquid or gaseous form, matter is known as a fluid. The common property of all fluids is that they must be bounded by impermeable walls in order to remain in an initial shape. If the restraining walls are removed the fluid flows (expands) until a new set of impermeable boundaries is encountered. Provided there is enough fluid or it is expandable enough to fill the volume bounded by a set of impermeable walls, it will always conform to the geometrical shape of the boundaries. In other words, a fluid by itself offers no lasting resistance to change of shape. The essential difference between a liquid and a gas is that a given mass of the former occupies a fixed volume at a given temperature and pressure whereas a fixed mass of a gas occupies any available space. A liquid offers great resistance to volumetric change (compression) and is not greatly affected by temperature changes. A gas or a vapour, on the other hand, is easily compressed and responds markedly to temperature changes.