Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jimijimi81 on 18/07/2009 19:28:23
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what would happen if u had a MASSIVE rod of unbreakable material, like many light years long. and then say u swung it like a bat ,, and u where superman (or goku) so ya could.
SURLEY the end of the rod would travel MUCH fatser than the speed O'light yeh? breakin that E=MC2 law.
Jimi
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Long rods are never rigid or unbreakable they bend and break. All solids are extrememly soft and weak when it comes to the sort of forces involved inlarge scale ideas like that. As you sweep the light of a torch round the room (or up into the sky the beam bends so the light stays at the same speed
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hang on,, ill be a bit more specific... theorecticly,, if one obtained or created a material with enourmous tensial streanth and ragitity.. enough to withstand the forces involved... then go into outer space,, and swung this rod aorund in a circle... the end of the rod many many light years away will travel at tremndous speed. the end of rod which u are holding would have only of traveled a metre of two... but the other end, the galaxies away would have taken the same time to go in full circle BUT the distance it has traveled would be MENTAL....
if not a rod then a HUGE galaxy sized disc,,
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At size scales of the kind that you have in mind, *all* materials are sort of "springy". If you take a rod whose length is the same as the diameter of the galaxy, and you try to whip it around, what will happen is that it will bend; there's no such thing as a perfectly rigid material. In fact, with the size scales you're thinking of, swinging a rod - even a really rigid one - is a lot more like swinging a string.
Instead of thinking of physical objects as being solid and continuous, think of them in terms of the atoms that they're made of. When you push an object, you push the atoms that your hand comes into contact with, and those atoms push the ones near them, who then push the ones near them, and so on. In that sense, force takes time to transmit through a material; you can't swing a rod at one end and have the other end respond immediately. The rod will always bend, and on a cosmic length scale, it'll bend at least as much as is necessary in order for no part of it to ever move faster than the speed of light.
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A rod of any material of any thicknes a few thousand miles (let alone millions or light years) long would rapidly collapse under its own self gravitation into a blob.
You seem to be completely unaware of the real world scale of things strengths and forces. The question is totally irrational
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I think it's a perfectly reasonable question; it only seems irrational if you already know the answer.
If gravity is that important to your sensibilities, you could think of a similar, but functionally equivilant, question - what if you had a really giant sphere, and had sufficient force to shove it really hard into something else. When it collides with that something else, is the signal of you shoving it traveling faster than the speed of light?
The same misconception is still at work - forces don't travel instantaneously through materials. In every day life, when you wave around a rod, or push a sphere, or anything else, the entire object appears to move all at once. But that's not what actually happens, and the difference is only obvious when you consider things that you don't worry about every day - like galaxy-spanning rods (or galaxy-spanning spheres, if you like).
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thanks mate