  We calculate a force due to zero-temperature quantum fluctuations on a
stationary object in a moving superfluid flow. We model the object by a
localized potential varying only in the flow direction and model the flow by a
three-dimensional weakly interacting Bose-Einstein condensate at zero
temperature. We show that this force exists for any arbitrarily small flow
velocity and discuss the implications for the stability of superfluid flow.
