# Why is this thought experiment flawed: A vast lever rotating faster than the speed of light [duplicate]

If there were a vast lever floating in free space, a rigid body with length greater than the width of a galaxy, made of a hypothetical material that could endure unlimited internal stress, and this lever began to rotate about its middle like a propeller so that a person looking at the universe would simply see it spinning at a gentle pace like a windmill, would not its ends be moving many, many times the speed of light?

Or am I making so many errors in my thought process that the whole question is absurd? I'm trying to establish why, in essence, a sufficiently large mechanical device (large beyond reason) could not exceed the speed of light.

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## marked as duplicate by John Rennie, Qmechanic♦May 9 '13 at 19:01

This question was marked as an exact duplicate of an existing question.

To imagine this, take your bicycle and try to rotate one of its wheels. As you put your finger closer to he centre, you need stronger force (but same energy of course) to get the wheel moving. So the distance from the centre ($r$) matters somehow obviously. And when you try to give the mass at the perimeter speed over $c$ (lightspeed), you are in the same situation as here.