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In 1851, George Gabriel Stokes derived an expression, now known as Stokes' law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers (i.e. very small particles) in a viscous fluid. Stokes' law is derived by solving the Stokes flow limit for small Reynolds numbers of the Navier–Stokes equations:〔Batchelor (1967), p. 233.〕 ==Statement of the law== The force of viscosity on a small sphere moving through a viscous fluid is given by: : where ''Fd'' is the frictional force – known as Stokes' drag – acting on the interface between the fluid and the particle, ''μ'' is the dynamic viscosity, ''R'' is the radius of the spherical object, and ''V'' is the flow velocity relative to the object. In SI units, ''Fd'' is given in Newtons, ''μ'' in Pa·s, ''R'' in meters, and ''V'' in m/s. Stokes' law makes the following assumptions for the behavior of a particle in a fluid: : *Laminar Flow : *Spherical particles : *Homogeneous (uniform in composition) material : *Smooth surfaces : *Particles do not interfere with each other. Note that for molecules Stokes' law is used to define their Stokes radius. The CGS unit of kinematic viscosity was named "stokes" after his work. 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」の詳細全文を読む スポンサード リンク
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