# Kinematic viscosity for water

The kinematic viscosity (also called momentum diffusivity) is the ratio of the dynamic viscosity $\mu$ to the density $\rho$.

It is a convenient concept when analyzing the Reynolds number, which expresses the ratio of the inertial forces to the viscous forces.

The sources are:

 $\frac{\eta_w}{\zeta_w}$ general equation $-1.312{\cdot}{10}^{-8} {\theta_w}^3+1.2973{\cdot}{10}^{-6} {\theta_w}^2-6.0154{\cdot}{10}^{-5} \theta_w+1.792{\cdot}{10}^{-3}$ fresh water
$\theta_w$
$\zeta_w$
Density of water [kg/m$^3$]
Used in
$\eta_w$
Choices
Liquid0.01°C10°C20°C25°C30°C
Fresh water1.7918e-061.3065e-061.0035e-068.927e-078.007e-07