Fluid Mechanics
fluid mechanics,?science?concerned with the?response of fluids?to forces exerted upon them. It is a branch of classical?physics?with applications of great importance in hydraulic and?aeronautical engineering,?chemical engineering,?meteorology, and zoology.
The most familiar fluid is of course?water, and an encyclopaedia of the 19th century probably would have dealt with the subject under the separate headings of?hydrostatics, the science of water at rest, and hydrodynamics, the science of water in?motion.?Archimedes?founded hydrostatics in about 250?BC?when, according to?legend, he leapt out of his bath and ran naked through the streets of Syracuse crying “Eureka!”; it has undergone rather little development since. The foundations of hydrodynamics, on the other hand, were not laid until the 18th century when mathematicians such as?Leonhard Euler?and?Daniel Bernoulli?began to explore the consequences, for a virtually continuous medium like water, of the?dynamic?principles that Newton had enunciated for systems composed of discrete particles. Their work was continued in the 19th century by several mathematicians and physicists of the first rank, notably G.G. Stokes and William Thomson. By the end of the century explanations had been found for a host of intriguing phenomena having to do with the flow of water through tubes and orifices, the waves that ships moving through water leave behind them, raindrops on windowpanes, and the like. There was still no proper understanding, however, of problems as fundamental as that of water flowing past a fixed obstacle and exerting a?drag force?upon it; the theory of potential flow, which worked so well in other?contexts, yielded results that at relatively high flow rates were grossly at variance with experiment. This problem was not properly understood until 1904, when the German physicist?Ludwig Prandtl?introduced the concept of the?boundary layer?(see below?Hydrodynamics: Boundary layers and separation). Prandtl’s career continued into the period in which the first manned aircraft were developed. Since that time, the flow of?air?has been of as much interest to physicists and engineers as the flow of water, and hydrodynamics has, as a consequence, become fluid?dynamics. The term fluid?mechanics, as used here, embraces both fluid?dynamics?and the subject still generally referred to as hydrostatics.