ABSTRACT
Motion of single particles can be further divided into three classes according to the extent of particle-fl uid interaction. The simplest case is one in which the particles have the same density as the fl uid at a low particle concentration so that the particles exactly follow the motion of fl uid. The second case is such that the particle concentration is fairly low and the fl uid induces the relative motion of particles but the particle motion does not affect the motion of fl uid. The third case is such that the particle motion and fl uid motion interact with each other by exchanging momentum. In this section, motions of single particles in the second case without particle-particle interaction are described.
