question_answer

Spherical balls of radii R are falling in a viscous fluid of viscosity \[\eta \] with a velocity \[\upsilon \]. How does the retarding viscous force acting on a spherical ball depend on R and \[\upsilon \]?                     

Answer:

                \[F=6\pi \eta R\upsilon \]i.e., retarding viscous force is directly proportional to both R and \[\upsilon \].