# Viscosity Coefficient

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Viscosity coefficient, abbreviated as $$\eta$$ (Greek symbol eta), also called coefficient of viscosity or absolute viscosity, is the tangential friction force required to preserve a unit velocity gradient between two parallel layers of liquid of unit area.  The greater the coefficient of viscosity the greater the force required to move the layers at a velocity.

## Viscosity Coefficient formula

$$\large{ \eta = \frac { F_t \; l } { A \; v } }$$
Symbol English Metric
$$\large{ \eta }$$  (Greek symbol eta) = viscosity coefficient $$\large{\frac{lbf - sec}{ft^2}}$$ $$\large{Pa - s}$$
$$\large{ A }$$ = area $$\large{in^2}$$ $$\large{mm^2}$$
$$\large{ l }$$ = distance between the layers $$\large{in}$$ $$\large{mm}$$
$$\large{ F_t }$$ = tangential force $$\large{lbf}$$ $$\large{N}$$
$$\large{ v }$$ = velocity $$\large{\frac{ft}{sec}}$$ $$\large{\frac{m}{s}}$$