Hydrodynamic friction on a moving molecule

Abstract

We present some calculations of the hydrodynamic drag on a molecule moving in a viscous fluid. The interaction of the molecule with the fluid is described by an intermolecular potential energy, rather than by imposing boundary conditions on a sharply defined surface. Our procedure requires solution of the Navier–Stokes equations for slow stationary flow of a viscous compressible fluid past a fixed force field. This is done here for two very simple models for the intermolecular potential: a ramp potential and a step potential. The results show that it is possible to calculate a drag force without imposing boundary conditions on a surface.