(published on 10/22/2007)
(published on 12/29/2011)
(published on 08/17/2012)
(published on 08/20/2012)
What it says is more that if you start to twist on one end of the rod, there has to be a slight delay before the other end responds, since no information can travel faster than c. In principle that delay only has to be 10 cm/c ≈ 3.3*10-10 s. In practice, the forces are mostly transmitted by the same sort of material stiffness that gives rise to the speed of (transverse) sound in the rod. So the response really starts up after about 10 cm/(speed of sound), maybe around 10-4 s.
Assuming the rotation is at some reasonable rate, however, the speed of the different parts ends up being just what you'd get from a simple classical calculation.
Mike W. (posted without checking until Lee gets back)
p.s. For a very cool video of how influences propagate from one end of an object to the other, you might want to look at . It uses a slinky, so the relevant waves propagate much slower than the sound waves in an ordinary rod.
(published on 05/27/2013)