Important frames

Three different coordinate frames will become important during the presentation:

1. Inertial frame: The global coordinate frame that is fixed with respect to all motions of interest.
2. Translating frame: A moving frame that has its origin at the center of mass of ${\cal A}$ and its axes aligned with the inertial frame.
3. Body frame: A frame that again has its origin at the center of mass of ${\cal A}$, but its axes are rigidly attached to ${\cal A}$. This is the same frame that was used to define bodies in Chapter 3.