The theoretical value for the moment of inertia of the plate is I = 4 . 54 × 10 − 4 kg m 2 . Figures 3 (a) and (b) show typical results of the tracking procedure performed by Tracker . In figure 3 (a), the reference frame, indicated by two white arrows, is shown in white and its axes are designated as x and y . The centre of the ball bearing is at the origin of the reference frame. The numbers, as shown in figures 3 (b) and (d), sho w the temporal de velopment of the tracked positions