# The CGS unit of viscosity is the poise. Find the relation between the poise and the SI unit of viscosity.

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The CGS unit of viscosity is the poise. Find the relation between the poise and the SI unit of viscosity.

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By Newton’s law of viscosity,

where $\frac{F}{A}$ is the viscous drag per unit area, $\frac{dv}{dy}$ is the velocity gradient and η is the coefficient of viscosity of the fluid. Rewriting the above equation as

SI unit : the pascal second (abbreviated Pa.s), 1 Pa.s = 1 N.m-2 .s

CGS unit: dyne.cm-2 .s, called the poise [symbol P, named after Jean Louis Marie Poiseuille (1799 -1869), French physician].

[Note : Thè most commonly used submultiples are the millipascalsecond (mPa.s) and the centipoise (cP). 1 mPa.s = 1 cP.]