Rotating Disc & Speed of Light ???!

[sabin]

If a point on a disc's outer edge is traveling close to the speed of light and things contract in the direction of the acceleration at those speeds (relative to a stationary observer) would that mean the disc's radius stays the same but the circumfrance shrinks???

This has been hurting my head for days, hope someone can shed some light on it.

[CarlB]

Choose a global set of coordinates and everything will be clear.

Carl

[jcsd]

It's called the Ehrenfest paradox, there's already a thread on it at the top of this forum:

http://www.physicsforums.com/showthread.php?t=128713

[MeJennifer]

If a point on a disc's outer edge is traveling close to the speed of light and things contract in the direction of the acceleration at those speeds (relative to a stationary observer) would that mean the disc's radius stays the same but the circumfrance shrinks???

This has been hurting my head for days, hope someone can shed some light on it.
That depends on your interpretation of what is happening.

In the theory of relativity the circumference indeed shrinks and as a result of the space in the rotating disk is no longer Euclidean but curved and pi is no longer a correct ratio. Furthermore by applying the equivalence principle we can deduce that the same applies to a gravitational field. :smile:

Alternatively one can interpret that the space remains Euclidean and that the shrinking will increase the stress on the material and that it either bends or bursts. :smile: