# Rotating Frames of Reference

1. Jul 19, 2006

### eep

Hi,
I've run into a relativistic kinematics question that I'm not sure how to approach. The question states:

"A source and a detector are spaced a certain angle $\phi$ apart on the edge of a rotating disk. The source emits radiation at frequency $\omega$ in it's instantaneous rest frame. What frequency is the radiation detected at? Hint: Little information is given because little is needed."

I have no idea how to approach this. Since the detector and source are on a rotating disk, they are not connected by inertial frames. I want to say that their instantaneous rest frames are somhow connected, that is, the relative velocities of the frames are always the same. But where do I even begin? I thought perhaps I could work out where the detector would receive a photon emmited by the source, and maybe do a lorentz boost from the instantaneous rest frame of the source to a frame where both detector appear to be moving on the edge of the disk, then do a boost from that frame to the frame of the detector using the velocity of the detector at the time it would be received, but that seems complicated... what am I missing here?

2. Jul 21, 2006

### George Jones

Staff Emeritus
Can you get hold of the book Gravitation by Misner, Thorne, and Wheeler? The solution to this problem is given in section 2.8 The Centrifuge and the Photon.

3. Jul 24, 2006

### eep

Thanks - picked the book up today, that thing weighs a ton!