Abstract In order to understand ball motions of new ultra-precision ball grinding machine, this study presents an mechanical model using a transparent acrylic container to simulate ball motions. The effects of float material, load, and process condition on the ball grinding characteristics at low shaft speed. The ball motions can be observed by the CCD camera to calculate the ball¡¦s circulation speed , the ball¡¦s spin angular speed and the ball¡¦s spin angle . Furthermore, the kinematic equations of ball motion is derived with different rolling sliding condition. The theoretical values of , , and are compared with the experimental values under pure rolling condition. Results show that the theoretical values are in good agreement with the ball¡¦s spin angular speed, but with larger error for and .This error is still in range of engineer error. Hence, at low shaft speed, contacts between balls and container, or shaft or float are close to the pure rolling conditions. Because the higher friction force between ceramic balls and alumina float, the ball¡¦s circulation speed with alumina float than that with acrylic float since fluid thrusts balls at low shaft speed, the ball¡¦s circulation speed in working fluid than that without working fluid. Since mass of float is light, it can be drive easily. Hence, with increasing the load which also increases the float mass, the float angular speed is decreased and the ball¡¦s circulation speed is also decreased.