Twisting ball display is promising as a candidate for Digital Paper but ball behavior must be clarified. We carry out basic experiments into ball behavior by using enlarged scale model balls. Threshold electric fields for bi-stable motion and response time when switching ball direction are measured under various conditions. A theoretical study on the moments of ball rotation is introduced. Driving moment of coulomb force is shown to dependent on electric field strength, difference in surface electric charge densities on the hemispheres, and ball diameter. An equation that yields ball rotation is described that is based on the coulomb force.