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Say you had a really long pole made of a super strong material, and at the you turned it through an angle of (for example) 45 degrees. Turning the pole through a small angle at the bottom would translate to a massive movement at the top of the pole, see picture:

Now, I did some calculations, and with "non-relativity" calculations came up with a scenario where moving the pole through a 45 degree angle in a minute would mean the pole would have to be approximately 24 billion meters tall for the top to go faster than 300,000,000 m/sec, according to Newtonian mechanics. Now, of course its not possible for the top to go faster than the speed of light, so what would happen? Would time dilation affect just the top and not the middle/bottom?

In the context of this question please assume that the material is super-super strong and somehow a future human race has found a way to build a 24 billion meter long pole, and that there's a planet somewhere where there are no other nearby objects with lots of gravity to pull the pole around in outer space. If these are entirely unrealistic assumptions (i.e. violates a law of physics), please say so!

Qmechanic
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Tdonut
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    http://physics.stackexchange.com/q/2774/ Also, you might have gotten a hint by looking at the answer to the "pushing a long pole" version: http://physics.stackexchange.com/q/2175/ – dmckee --- ex-moderator kitten Aug 17 '15 at 01:24
  • Choosing the wrong tag may have contributed to that not coming up in the similar questions you get when you start a new question. – dmckee --- ex-moderator kitten Aug 17 '15 at 01:25
  • Lets imagine it is possible to build a super-long pole that won't bend and reacts instantly, which probably isn't possible, but lets say it is. You still face the relativistic mass problem, where the mass gained as the tip approaches the speed of light would make moving it at the point you are holding, increasingly difficult. At least, it would require an infinite amount of energy for the tip to approach c cause the mass grows exponentially with each decimal point closer to c. (.9c, .99c, .999c, etc). Nice try though, but the laws of physics win again. – userLTK Aug 17 '15 at 01:40
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    Not "just probably isn't possible": absolutely isn't possible as it requires that the atoms at the far end learn about what happened at the near end faster than light speed allows. When you start considering things that would ideally violate relativity ductility becomes compulsory. – dmckee --- ex-moderator kitten Aug 17 '15 at 01:42
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    (1) there are no rigid bodies in SR and (2) except for the end of the pole at the center of rotation, each segment of the pole is in a different, accelerated reference frame. In other words, 'ordinary' SR reasoning is not applicable here. Consider, for example, the nuances of a rotating disk. https://en.wikipedia.org/wiki/Ehrenfest_paradox – Alfred Centauri Aug 17 '15 at 01:51
  • So, it's impossible squared, or, maybe impossible cubed. :-) – userLTK Aug 17 '15 at 02:13

1 Answers1

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In the context of this question please assume that the material is super-super strong and somehow a future human race has found a way to build a 24 billion meter long pole, and that there's a planet somewhere where there are no other nearby objects with lots of gravity to pull the pole around in outer space. If these are entirely unrealistic assumptions (i.e. violates a law of physics), please say so!

It violates the speed of light limit by which information can travel up your pole, in this case information for "turn". All interactions in solid state materials we know in the universe are electromagnetic . The strength of the pole is built up by electromagnetic interactions. Any transfer of motion to the pole at the particle level of the constituents of the pole transfer the energy and impulse with electromagnetic interactions. Those are bounded by c, the velocity of light.

anna v
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