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Stokes, Sir George Gabriel

law fluorescence oil hydrodynamics

(1819–1903) Irish physicist: a contributor to fluid dynamics.

Educated in his native Ireland and at Cambridge, Stokes became Lucasian professor at Cambridge in 1849 and in the next half-century did much to rescue physics teaching there. He worked in most areas of theoretical and experimental physics except electricity. One of his enthusiasms was hydrodynamics and another was fluorescence, and both have laws named after him. Stokes’s Law in hydrodynamics is that the frictional force (ie drag) on a spherical body of radius r moving at its terminal speed v through a viscous fluid of coefficient of viscosity n is 6p nr v; this holds only for a restricted range of conditions. Stokes’s Law of Fluorescence states that the wavelength of fluorescence radiation is greater than that of the exciting radiation; again, the law does not always hold.

He pioneered in 1849 studies of gravity variations over the Earth’s surface: such geophysical methods are now used in stratigraphic studies to assist oil prospecting. An ultrasensitive spring balance (gravimeter) is used, allowing the acceleration due to gravity ( g ) to be measured; a low value indicates a low density material (oil or water) .

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