ABSTRACT
A simple example of a velocity eld v having a nonzero curl, in spite of the fact that its streamlines dene a family of parallel straight lines, is provided by Poiseuille's ow, which is a laminar (nonturbulent), steady, viscous ow at low velocities in a cylindrical tube, and is subject to a given constant pressure gradient along its axis (see Figure F.1.)
Figure F.1: Viscous ow at low velocities in a cylindrical tube.
