roger
Penultimate Amazing
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Yes, he is correct. As the thread has stated, it would move at the speed of sound in that object.
A Physics Question
- Thread starter kaisersean
- Start date
I posted this once before, but how far off, well, other than by a few dozen orders of magnitude, are we with this
Well, the material may be dispersive, as well, so different frequencies in the original impulse may arrive at slightly different times, and resonance phenominon will also affect information transfer, but the speed of sound is the fastest that any information can get there, indeed.
Thanks I was not sure that was what he was stating, fascinating concept when taken to the extreme. So ‘theoretically’ if the light year long bar was pushed and you observed a distance travelled of 1 meter, the other end would not move for some X of years!
Angus McPresley
Muse
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I once had a similar thought about a giant LP record, sitting on a record player. Even at a mere standard 33 1/3 revolutions per second, if the record was big enough, then the outer edge would be moving at greater than the speed of light. An impossibility.
Obviously a record that big wouldn't hold together, but really, is there an Einsteinian limit on how strong the chemical bonds holding the record together can be? How exactly is this (gedanken) experiment officially foiled by relativity?
Obviously a record that big wouldn't hold together, but really, is there an Einsteinian limit on how strong the chemical bonds holding the record together can be? How exactly is this (gedanken) experiment officially foiled by relativity?
You're still trying to accelerate the particles on the edge of the record player to beyond light speed, this is going to require an infinite amount of force to do so, as the particles get heavier and heavier the closer they get to moving at c. So long as the chemical bonds are not infinitely strong it won't work.
3point14
Pi
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I don't understand it at all - but I think this is what you're talking about?
http://math.ucr.edu/home/baez/physics/Relativity/SR/rigid_disk.html
Or maybe I'm misinterpreting (again, sigh)
I like this one though - it amuses me, and I think I nearly get it (doubtful)
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
Damn, I wish I were clever.
http://math.ucr.edu/home/baez/physics/Relativity/SR/rigid_disk.html
Or maybe I'm misinterpreting (again, sigh)
I like this one though - it amuses me, and I think I nearly get it (doubtful)
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
Damn, I wish I were clever.
Nucular
Illuminator
Ah, it was this exact thing that first made me realise that science is, well, pretty cool.
It occurred to me as I was gazing out of the sixth form block window - my version was a bit less plausible, as it involved, for the sake of argument, a light-year long stick, tapping across space in morse code. I ran it by a science-minded mate (who later went off and worked at the CERN particle accelerator, to my eternal jealousy), who got mildly doubtful but a bit excited, so we went off to find a science teacher.
Mr Murdin obligingly demolished my idea in about three minutes of patient blackboarding, with a single equation and a crystal-clear explanation. In those three minutes, my vague ideas of a Nobel Prize and a cushy university chair dissolved into a much more useful appreciation for science, and what it tells us about the world in those (to me) incomprehensible formulae.
Too late for my science GCSE (though I did okay in a John Searle 'Chinese Room' kind of way), and too late to change my arty farty A-Level choices, but soon enough for me to change a lot of my opinions about things I assumed that, because I didn't understand them, were meaningless.
Good old Mr. Murdin. Good old science.
It occurred to me as I was gazing out of the sixth form block window - my version was a bit less plausible, as it involved, for the sake of argument, a light-year long stick, tapping across space in morse code. I ran it by a science-minded mate (who later went off and worked at the CERN particle accelerator, to my eternal jealousy), who got mildly doubtful but a bit excited, so we went off to find a science teacher.
Mr Murdin obligingly demolished my idea in about three minutes of patient blackboarding, with a single equation and a crystal-clear explanation. In those three minutes, my vague ideas of a Nobel Prize and a cushy university chair dissolved into a much more useful appreciation for science, and what it tells us about the world in those (to me) incomprehensible formulae.
Too late for my science GCSE (though I did okay in a John Searle 'Chinese Room' kind of way), and too late to change my arty farty A-Level choices, but soon enough for me to change a lot of my opinions about things I assumed that, because I didn't understand them, were meaningless.
Good old Mr. Murdin. Good old science.
Walter Wayne
Wayne's Words
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- Jul 26, 2002
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No one ever refers to a ship falling apart as it approaches a linear velocity of c, in spite of the fact that similar sheer forces would happen in the ship as in the spinning record. The force is applied at the rockets are whatever propulsion system is used, and then distributed thoughout the ship via chemical bonds.
In linear motion, your mass approaches infinity as you approach c. Also as your mass gets larger the acceleration association with a force becomes diminishingly small. As a result we find that as you approach c, mass and kinetic energy approaches infinity and we also find that a body under a constant force will approach c asymptotically.
In the case of a spinning disc you get similar results. Your moment of inertia, a measure of a body's resistance to angular acceleration, approaches infinity as you approach c. Also as your mass gets larger the angular acceleration association with a torque becomes diminishingly small. As a result we find that as you approach c, moment of inertia and rotational energy approaches infinity and we also find that the edge of a body under a constant torque will approach c asymptotically.
As Jekyll pointed out the particles on the edge of the record become quite massive, and thus require infinite energy to accelate to c. If you want to relate that to rotational dynamics, torque is the product of force multiplied by the distance to the centre of rotation (if the force is perpendicular to the radius). Thus as force approaches infinity, torque does as well. Moment of inertia is related to the mass of the particle multiplied by the square of the distance to the centre. Again, as mass approaches infinity so does moment of inertia.
The difficulty in doing the calculation for the spinning disc, is that the moment of inertia can be difficult to find. The velocity of different section of the disc vary with distance from the spindle, and thus the density increases as you move away from the centre. I once started to calculate the moment of inertia of a spinning rod taking into account relativistic affects. I quickly got to an integral I couldn't solve, and which may not have a closed form solution.
Walt
In linear motion, your mass approaches infinity as you approach c. Also as your mass gets larger the acceleration association with a force becomes diminishingly small. As a result we find that as you approach c, mass and kinetic energy approaches infinity and we also find that a body under a constant force will approach c asymptotically.
In the case of a spinning disc you get similar results. Your moment of inertia, a measure of a body's resistance to angular acceleration, approaches infinity as you approach c. Also as your mass gets larger the angular acceleration association with a torque becomes diminishingly small. As a result we find that as you approach c, moment of inertia and rotational energy approaches infinity and we also find that the edge of a body under a constant torque will approach c asymptotically.
As Jekyll pointed out the particles on the edge of the record become quite massive, and thus require infinite energy to accelate to c. If you want to relate that to rotational dynamics, torque is the product of force multiplied by the distance to the centre of rotation (if the force is perpendicular to the radius). Thus as force approaches infinity, torque does as well. Moment of inertia is related to the mass of the particle multiplied by the square of the distance to the centre. Again, as mass approaches infinity so does moment of inertia.
The difficulty in doing the calculation for the spinning disc, is that the moment of inertia can be difficult to find. The velocity of different section of the disc vary with distance from the spindle, and thus the density increases as you move away from the centre. I once started to calculate the moment of inertia of a spinning rod taking into account relativistic affects. I quickly got to an integral I couldn't solve, and which may not have a closed form solution.
Walt