while it is relatively easy to visualize the power flow through a conventional gear train and observe the directions of motion for its member gears, it is very difficult to determine the behavior of a planetary train by observation. we must do the necessary calculations to determine its behavior and may be surprised at the often counterintuitive results. since the gears are rotating with respect to the arm and the arm itself has motion, we have a velocity difference problem here which requires equation 6.5 (p.243) be applied to this problem. Rewriting the velocity difference equation in terms of angular velocities specific to this system , we get