- #36
PeterDonis
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Sagittarius A-Star said:Why shall the radius contract?
It will contract if the ring is spun up in such a way as to make it contract.
Sagittarius A-Star said:the direction of the radius is perpendicular to the direction of motion and therefore not lenght-contracted
You are confusing length contraction as a frame-dependent effect, which has nothing to do with dynamics, with the dynamics of spinning up the ring. The dynamics of spinning up the ring must deform the ring, and there is a continuous range of possible solutions for how the ring deforms. One endpoint of that range is all radial deformation--the radius of the ring contracts enough to keep the tangential separation between atoms in the ring, in the instantaneous rest frame of each atom, constant. See my post #24.