Section 2 of the STAR paper by Bender, Erleben, Trinkle, Coumans * (1) try to derive equations (5) and (6) and convince yourself that they make sense physically. * (2) why does equation (8) have a cross product term? Where does it come from? * (3) below equation (8) is discussion stating that the inertia matrix is constant when the quantities in equations (7) and (8) are expressed in the body-fixed frame and time varying when they are expressed in the world frame. Why?