Abstract
The velocities, accelerations and drag forces experienced by two equal spheres freely-falling along their line of centres, or by two equal-sized spheres linked each other with a fine string, are determined at low Reynolds numbers. In contrast to the theoretical results obtained by applying the Stokes approximation for two equal spheres, the upper sphere falls faster than the lower sphere and the drag coefficients vary with Reynolds number even at the Reynolds numbers below 0.1. Flow visualization technique described in part 1 is applied to visualize streamlines around pairs of spheres falling along their line of centres.
