11.2 Frames of Reference
We have discussed the most commonly used Cartesian Coordinate System. In effect, a frame of reference is any coordinate system relative to which measurements are taken. For example, the position of a table in a room can be described relative to the walls of the room, making the room the frame of reference. Similarly, the laboratory is the reference frame for measurements taken there. If the same experiment is performed in a moving train, the train becomes the frame of reference. The position of a spaceship can be described relative to the position of the home stars; the system of home stars is then the frame of reference.