# Reaching speed of light [duplicate]

Possible Duplicate:
Rotate a long bar in space and reach c

Sorry this is very naive, but it's bugging me. If you had a straight solid stick attached on one end and rotating around that attachment at a certain rpm, there would be a length at which the end of the stick would theoretically reach, with that rpm, the speed of light. Well, doesn't seem possible - what specifically would be the limitations that would prevent the end of the stick to reach the speed of light? What would happen?

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simply as a practical matter, it's doubtful you could find a material strong enough to withstand the tension to supply the necessary centripetal force. –  JustJeff Jan 17 '11 at 0:53
Voted to close as duplicate: the question has the same answer. –  Sklivvz Jan 17 '11 at 1:06
I agree, it's a duplicate; closed. –  Noldorin Jan 17 '11 at 1:16
Maybe we should all just admit once and for all that relativity applies to everything in the universe except really long sticks ;-) –  Greg P Jan 17 '11 at 16:30

## marked as duplicate by Colin K, Sklivvz♦, NoldorinJan 17 '11 at 1:16

In order for the bit of matter of mass $m$ at the very end of the stick to continue moving in a circular path of radius $R$ at a speed approaching the speed of light, it would need to be pulled toward the center with a force whose magnitude is

$|F| = |p|\frac{|V|}{R} = \frac{1}{\sqrt{1-(v/c)^2}}\frac{mv^2}{R}$

(the centripetal force you learn about in introductory physics). That force becomes infinitely large as the speed v approaches the speed of light, very rapidly, and eventually exceeds the strength of any interatomic or intermolecular forces that might be trying to hold the object together.

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obviously something's going to stop you from getting to c, but what about getting to interesting fractions of c, say, just enough for relativistic effects to become noticable? –  JustJeff Jan 17 '11 at 1:10