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Is relativistic effect of length contraction physically real ? 
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#1
Jun708, 10:09 AM

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Is Lorentz contraction a real contraction? For example, if one tries to accelerate a solid body, does its contraction require an extra input of energy to squeeze the atoms of the body closer together? Will this extra energy go into the total mass of the moving body?



#2
Jun708, 10:39 AM

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It's very real, but not in that sense. This should be obvious if you consider that it doesn't matter if it's the object or you who changed velocity.



#3
Jun708, 11:59 AM

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It is physically real, this can be seen by the fact that particle accelerators require relativistic corrections to the "bunch length" in order to determine the interactions of the particles.
Lorentz contraction is strainfree, as can be measured by a strain gauge, so it does not require additional energy. Don't forget that the fields around an atom also length contract. 


#4
Jun708, 02:30 PM

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Is relativistic effect of length contraction physically real ?
a moving object and a stationary object cant both be shorter than the other. 1 really shrinks. the other only APPEARS to shrink when viewed by the first. http://www.physicsforums.com/showthread.php?t=236978 


#5
Jun708, 02:37 PM

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if one tries to accelerate a solid body, does its contraction require an extra input of energy to squeeze the atoms of the body closer together? 


#6
Jun708, 03:03 PM

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That question, already answered, is no. An object does not contract in its own frame.



#7
Jun708, 03:19 PM

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Bernard Schutz, in his book, indicates that Lorentz contraction does require an extra input of energy to squeeze the atoms of the body closer together. Is there any one who agrees with him?
see this link http://books.google.com/books?id=jR3...1QKBq60HBbUyM 


#8
Jun708, 03:26 PM

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If you accelerate a real object by pushing it at one end, you will compress it a bit, but if you don't break it, every microscopic piece of it will restore itself to its original rest length in comoving inertial frames. This will heat the object a bit, so the work you perform when you push the rear of the object doesn't get converted to forward motion with 100% efficiency. This is an effect that doesn't really have anything to do with relativity, so I assume that this isn't what you had in mind. A Lorentz contraction is real in the sense that objects really do get shorter or longer when your velocity relative to the object changes (regardless of whether it was you or the object that accelerated). It's not just that that they appear to get shorter or longer. The reason why lengths change is that your velocity is what determines which 3dimensional "slice" of spacetime you will consider space. (There's nothing more important than this in all of SR, so you should try really hard to understand it if you're at all interested). Two observers who measure the length of the same object will disagree because they are measuring the lengths of different paths in spacetime. So why did I say "if the acceleration is linear..."? Because there are situations where it just isn't possible for each microscopic piece to restore itself to its original length in comoving inertial frames. The simplest example is a rotating disc. When you give a wheel a spin, the material will be forcefully stretched everywhere along the circumference by a factor that exactly compensates for the Lorentz contraction. So in this case we are performing additional work, not to cause the Lorentz contraction but to make sure that lengths remain the same when they do get Lorentz contracted. 


#9
Jun708, 03:44 PM

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Originally Posted by granpa View Post
a moving object and a stationary object cant both be shorter than the other. 1 really shrinks. the other only APPEARS to shrink when viewed by the first. This is completely false. A describes B the same way B describes A. how does that contradict what i said?? 


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Jun708, 03:48 PM

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#11
Jun708, 03:55 PM

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#12
Jun708, 03:58 PM

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#13
Jun708, 04:04 PM

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a moving object and a stationary object cant both be shorter than the other. 1 really shrinks. the other only APPEARS to shrink when viewed by the first due to loss of simultaneity. you obviously didnt even look at the link i posted.



#14
Jun708, 04:20 PM

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#15
Jun708, 05:10 PM

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But the first also "appears to shrink" when viewed by the other, for the same reason.
thats where you are wrong. its not for the same reason, as i clearly showed and proved mathematically in the link i posted. but it is impossible to tell which is real and which isnt. 


#16
Jun708, 05:28 PM

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#17
Jun708, 05:36 PM

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#18
Jun708, 05:53 PM

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http://www.physicsforums.com/showthread.php?t=236978 


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