If I were to drop a sphere down a tube of fluid. What are the effects of the wall of the tube on the sphere? Assuming the sphere has an extremely low Reynolds number of less than 1. Is it right to say that the ratio of the radius of the tube and the radius of the sphere has an effect on the terminal velocity of the falling sphere? At what ratio of the the two radius will the effect be negligible and at what ratio will the effect be apparent?