Recent content by thequantumcat

So then is this correct: S is at rest--inertial frame. u is speed of object in that frame S' is "moving observer" and its speed is v u' is the speed of object in S' (i.e speed as seen by this frame) In that case, the velocity formula would be: u = (u' - v)/(1-(u'v/c^2)) ?? I am confused...

I am, and no. I think if I can grasp the set up, then I'll be able to show the gamma's, and momentum and energy equations are fine.

Yes this is SR. I am confused about the actual formula. In this case, what is v, u' and u to plug into the velocity addition formula. Moreover, what exactly is the frame at "rest"? The full question is actually:

I can't seem to wrap my head around it: if an object is moving at speed v in frame S, and its observed to move at speed v' in S', what is the relationship?