THE FORCE ON A BUBBLE, DROP, OR PARTICLE IN ARBITRARY TIME-DEPENDENT MOTION AT SMALL REYNOLDS-NUMBER

The hydrodynamic force on a body that undergoes translational accelera tion in an unbounded fluid at low Reynolds number is considered. The r esults extend the prior analysis of Lovalenti and Brady [to appear in J. Fluid Mech. (1993)] for rigid particles to drops and bubbles. Simil ar behavior is shown in that, with the inclusion of convective inertia , the long-time temporal decay of the force (or the approach to steady state) at finite Reynolds number is faster than the t-1/2 predicted b y the unsteady Stokes equations.