The flow field generated by a moving sphere (Eq. (18)) is essentially independent of the sphere's radius when viewed at sufficiently large distances. Consequently, we may approximate the flow field around a sphere driven through an unbounded fluid by the flow due to a unit force on a point within the fluid. The corresponding Oseen tensor is the Green's function for the system:

This Green's function plays an important role in many hydrodynamic problems and is known as a

David G. Grier 2001-01-16