Question

A typical river-borne silt particle has a radius of $20\mu m$ and a density of $2\times {10}^{3}kg/m^3$. The viscosity of water is $1.0\text{milli-poise}$. Find the terminal speed with which such a particle will settle to the bottom of a motionless volume of water.

Answer 1

Using $V=\frac{2}{9}\frac{r^2(\rho -\sigma )g}{\eta }$
$\eta =1.0$ m $Pi=1.0\times {10}^{-3}Pi$
$=\frac{2}{9}\frac{{(20\times {10}^{-6})}^2\times (2\times {10}^3-{10}^3)\times 9.8}{1.0\times {10}^{-3}}$
$=0.882$ mm/s