Philosophy of Physics: A Very Short Introduction (Very Short Introductions)

by David Wallace

The content of the relativity principle is now that physics can be done equally well using the standard of motion defined by any inertial frame—it doesn’t have to be the rest frame. And, indeed, we can (mostly) see this just by looking at Newton’s laws: the First Law says that a force-free body either remains at rest or moves at constant velocity, but if a body does so relative to one inertial frame, it does so relative to all inertial frames. And the Second Law relates acceleration to force—but because acceleration is rate of change of motion, the acceleration of a body is the same in any inertial frame. What we require to do physics then, is some inertial frame or other. Given one such frame, we can construct indefinitely many other such frames—but we don’t need to know which frame is the rest frame, and indeed, we can’t know, because of the relativity principle.

rest frame and inertial frame uniform acceleration & uniform "velocity boost" main. multiple frame. relative