niiicholas
Posts: 319 Joined: May 2002

Fun article, a latter day version of Purcell's "Life at Low Reynolds Number":
The efficiency of propulsion by a rotating flagellum http://www.pnas.org/cgi/content/full/94/21/11307
Quote  Proc. Natl. Acad. Sci. USA Vol. 94, pp. 1130711311, October 1997 Biophysics The efficiency of propulsion by a rotating flagellum (bacteria / motility / hydrodynamics / low Reynolds number)
Edward M. Purcell*
Department of Physics, Harvard University, Cambridge, MA 02138
Communicated by Howard C. Berg, Harvard University, Cambridge, MA, July 29, 1997
ABSTRACT
[At very low Reynolds number, the regime in which fluid dynamics is governed by Stokes equations, a helix that translates along its axis under an external force but without an external torque will necessarily rotate. By the linearity of the Stokes equations, the same helix that is caused to rotate due to an external torque will necessarily translate. This is the physics that underlies the mechanism of flagellar propulsion employed by many microorganisms. Here, I examine the linear relationships between forces and torques and translational and angular velocities of helical objects to understand the nature of flagellar propulsion.]

Note: the mathematical tractability of calculating diffusion and velocity for bacteria & their flagella should not be neglected. E.g. it seems that the propulsion or dispersal potential of various "crude" flagella could be calculated.
