nizmo Posted June 10, 2009 Share Posted June 10, 2009 Hypothetical question here. Lets say you have a peice of rope 1000 light years long, and you have someone on each end of the rope. the rope is pulled tight (so no slack). If one person pulls the rope, will the other person feel the pull instantly, or will it take time for the force to travel across the rope? Link to comment Share on other sites More sharing options...
J.C.MacSwell Posted June 10, 2009 Share Posted June 10, 2009 Hypothetical question here. Lets say you have a peice of rope 1000 light years long, and you have someone on each end of the rope. the rope is pulled tight (so no slack). If one person pulls the rope, will the other person feel the pull instantly, or will it take time for the force to travel across the rope? It will take more than a thousand years regardless of what the rope is made of. Link to comment Share on other sites More sharing options...
Sisyphus Posted June 10, 2009 Share Posted June 10, 2009 What that thought experiment demonstrates is that there is a limit to how rigid anything can be. Nothing can transmit force at faster than the speed of light. Link to comment Share on other sites More sharing options...
iNow Posted June 11, 2009 Share Posted June 11, 2009 Basically, as mentioned above, there's no such thing as a perfectly rigid object. No matter what you use... rope, pipe, buckyball tubes... when you pull on one end, it causes a wave (of sorts) to travel down that object. You pull, and the molecules closest to your hand will tug at the molecules just a little further away from your hand. Then, those molecules which just experienced the tug will begin to tug at the molecules on the other side... the molecules even further away from your hand... and those molecules then tug at the molecules further away from them, and then they tug at the molecules on their other side (the side further away from you)... until finally those last few molecules at the other end of your object tug for the last time and there is no more rope... no more tugging... the reaction is essentially done (although, there would likely be some bounce back until an equilibrium was re-achieved, but that's not relevant for the purposes of this example). That tugging of molecules takes time, and each tug is a single event with a non-zero amount of time taken for it to happen... Add them all together, and THAT's how long it takes for the other end to move. Link to comment Share on other sites More sharing options...
ajb Posted June 11, 2009 Share Posted June 11, 2009 There are no rigid rods in special relativity. Something else that may interest you is the so called ladder paradox. Link to comment Share on other sites More sharing options...
granpa Posted June 11, 2009 Share Posted June 11, 2009 it will transmit at the speed of sound. picture the rope as a slinky Link to comment Share on other sites More sharing options...
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