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When observing an object, such as a spinning ring, what velocity is used to calculate its length contraction? I know it depends on the observer, but let's say theoretically an observer is just watching a spinning ring from a bird's-eye view, is the angular or tangential velocity used to calculate the ring's length contraction?

Alex Ambruso
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  • If you are talking about measuring, neither. Do you mean calculate? – BioPhysicist Mar 18 '19 at 16:34
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    Spinning and rotating objects are not trivial in relativity. This is to do with the fact that spinning involves acceleration, and you then have to be careful in applying relativistic tranformations. I don't think I can explain it here, so I will humbly advice to google 'Ehrenfest paradox' (https://en.wikipedia.org/wiki/Ehrenfest_paradox) – Cryo Mar 18 '19 at 21:06
  • Related: https://physics.stackexchange.com/questions/364945/a-question-about-the-ehrenfest-paradox –  Mar 19 '19 at 02:13

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