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Stokes law of sound attenuation is a formula for the attenuation of sound in a Newtonian fluid, such as water or air, due to the fluid's viscosity. It states that the amplitude of a plane wave decreases exponentially with distance traveled, at a rate given by : where is the dynamic viscosity coefficient of the fluid, is the sound's frequency, is the fluid density, and is the speed of sound in the medium:〔Stokes, G.G. "On the theories of the internal friction in fluids in motion, and of the equilibrium and motion of elastic solids", ''Transaction of the Cambridge Philosophical Society'', vol.8, 22, pp. 287-342 (1845〕 The law and its derivation were published in 1845 by physicist G. G. Stokes, who also developed the well-known Stokes' law for the friction force in fluid motion. ==Interpretation== Stokes' law applies to sound propagation in an isotropic and homogeneous Newtonian medium. Consider a plane sinusoidal pressure wave that has amplitude at some point. After traveling a distance from that point, its amplitude will be : The parameter is dimensionally the reciprocal of length. In the International System of Units (SI), it is expressed in neper per meter or simply reciprocal of meter (). That is, if , the wave's amplitude decreases by a factor of for each meter traveled. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stokes' law of sound attenuation」の詳細全文を読む スポンサード リンク
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