4/25/2021 Fluid mechanics -- Britannica Online Encyclopedia
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.
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4/25/2021 Fluid mechanics -- Britannica Online Encyclopedia
One other representative of the 20th century who deserves mention here besides Prandtl is
Geoffrey Taylor of England. Taylor remained a classical physicist while most of his
contemporaries were turning their attention to the problems of atomic structure and quantum
mechanics, and he made several unexpected and important discoveries in the field of fluid
mechanics. The richness of fluid mechanics is due in large part to a term in the basic equation
of the motion of fluids which is nonlinear—i.e., one that involves the fluid velocity twice over.
It is characteristic of systems described by nonlinear equations that under certain conditions
they become unstable and begin behaving in ways that seem at first sight to be totally chaotic.
In the case of fluids, chaotic behaviour is very common and is called turbulence.
Mathematicians have now begun to recognize patterns in chaos that can be analyzed fruitfully,
and this development suggests that fluid mechanics will remain a field of active research well
into the 21st century. (For a discussion of the concept of chaos, see physical science, principles
of.)
Fluid mechanics is a subject with almost endless ramifications, and the account that follows is
necessarily incomplete. Some knowledge of the basic properties of fluids will be needed; a
survey of the most relevant properties is given in the next section. For further details, see
thermodynamics and liquid.
Citation Information
Article Title: Fluid mechanics
Website Name: Encyclopaedia Britannica
Publisher: Encyclopaedia Britannica, Inc.
Date Published: 17 January 2019
URL: https://www.britannica.com/science/fluid-mechanics
Access Date: April 24, 2021
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