Does the theory of relativity include angular motion? Say we have one body synchronously orbiting a motionless body. It can also be viewed as two motionless bodies and one is spinning while the other is not. (i.e. if you were on the moon starring at earth, you would not witness orbital motion). But we KNOW that the moon orbits the earth, so then is this kind of motion not relative? Would it be more appropriate to say that the two bodies orbit each other with some constant center of mass? And, clearly there is a difference between a spinning object and non-spinning object (in the way of centrifugal forces) so there is evidence that rotation is not relative. Any thoughts on this?