Question

CGS unit of viscosity is Poise. Find the relation between Poise and the SI umt of viscosity.

Answer 1

By Newton’s law of viscosity,

`F/A = eta (dv)/dy`

Where `F/A` is the viscous drag per unit area, `(dv)/dy` is the velocity gradient, and η is the coefficient of viscosity of the fluid. Rewriting the above equation as:

η = `(F//A)/(dv//dy)`

[η] = `([F A^-1])/([dv/dy])`

= [ML⁻¹T⁻²]

= [ML⁻¹T⁻¹]

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].