  An analytic expression is derived for a force on a weak point impurity
arising from the scattering of quantum fluctuations in a slow-moving, weakly
interacting, three-dimensional Bose-Einstein condensate at zero temperature. In
an infinitely extended geometry, this force is shown to exist at any
arbitrarily small flow velocity below Landau's critical velocity. Furthermore,
this force is shown to be directly proportional to the flow speed.
