Under $20C,$ particles assumed to be perfect spheres with a density of $1\mathrm{.}8\frac{g}{c}{m}^3$ have the

following radii and settling velocities in water. The velocities are calculated by equating the

drag force calculated from Stoke's Law to the gravitational force acting on the sphere:

$6r{V}_s=\frac{4}{3}{r}^3({}_2-{}_1)g$ and rearranging to give the velocity as:

$v_s=\frac{2({}_2-{}_1)g{r}^2}{9}($or in terms of $d_p$;$v_s=\frac{({}_2-{}_1)g{d}_p^2}{18})$

Check if Stoke's Law is valid for these particles, if not find the true velocity.

$=0\mathrm{.}01\frac{g}{c}\frac{m}{s}(at20C)$