The mechanism of particle separation was analyzed by use of the methods of particle reentrainment by airflow and centrifugal separation. Glass beads of six different sizes in a range of 21.8-100.6 mu m in count median diameter were used, and the drag and centrifugal forces for particle separation were obtained experimentally. A moment balance model based on adhesive, gravitational, and separational forces was presented on an assumption of Hertzian deformation in a particle-wall contact zone. The model corresponding to each experimental method was formulated, and adhesive force was calculated from the separation force. It was found that the values of the adhesive force agreed with each other irrespective of the experimental methods, showing the analysis based on the moment balance was more reliable. Furthermore, the values of adhesive force obtained from the experiments were compared with various theoretical ones, and it was found that the adhesive force agreed approximately with van der Waals force.