$($b$)$ The equation of motion for the particles moving in a fluid under the action of a centrifugal field is similar to that for motion in the gravitational field, except that the gravitational acceleration $g$ must be replaced by the centrifugal acceleration $r{}^2,$ where $r$ is the radius of rotation and $$ is the angular velocity. Assuming that the particles are spherical and that the show $\frac{dt}{dt}=|{|}_t(\frac{r{}^2}{g})$ where $u_t$ is the terminal velocity. $|6|$