Forces on solid particles and their effects on particle motion are investigated and discussed in the paper. Comparison of magnitude method and function method are applied to analyze the importance of drag force, added mass force, Magnus force, Saffman force and Basset force. The revised and improved BBO equation is established for the solid particles in the teetered bed separator. Various factors influencing the particle velocities are obtained through the dimensional analysis method. The results show that the gravity, buoyancy force, drag force, added mass force and Basset force are the dominant forces in the particle movement. The larger the particle diameter is, the greater the drag force is on the particle. The teeter water makes the flow field unsteady and heterogeneous, when going through the distribution plate. Magnus force is produced by the local vortex at the bottom of the column and must be considered compared with drag force. However, Magnus force can be neglected except for the area above the distribution plate. Because the teeter water velocity in the radial direction is quite smaller than that in the axial direction, Saffrnan force on solid particles has little effect on particle movement. Basset force on movement particles is smaller and smaller over time.
