Relativity paradox

Discussion in 'Physics & Math' started by renislaj, Apr 18, 2013.

  1. Tach Banned Banned

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    I told you that the free lessons are over.

    What don't you understand in the "free lessons are over"?
     
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  3. Undefined Banned Banned

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    You mean the "lessons" in playing games, wasting people's time, insulting and trolling because you are wrong or because you are afraid of being proven wrong out of your own mouth if you answer my questions about what you say but don't support? The only "free lesson" I have had from you is on how you confuse and muddy discussions such that threads become almost unreadable because of your "gamesmanship" posts cluttering everything. These unscientific "lessons" are not what I came to sciforums for. Thankyou but no thankyou. I will ignore you from now on unless you answer my last request for you to explain why you said the train and the platform frames are both "accelerated" frames. Will you please explain now what you meant there, as I have humbly requested, so that I may learn from you some "lessons" worth learning, instead of what you have offered me so far?
     
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  5. Fednis48 Registered Senior Member

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    Er, I'm having a really hard time parsing your English here. But you say "once motion of rod is established as a constant closing speed", which makes me think you're confusing this thread with the other one. If the rod is moving at constant speed (other thread), all three frames are inertial. If the rod is dropping under gravity, it's inertial and the other two frames are accelerating up by comparison.
     
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  7. Undefined Banned Banned

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    Yes, you are right. I am thinking about the other thread of your and Pete's SR only formalism. Maybe I am thinking of this thread too, because even in this GR inclusive scenario we can make gravity so "weak field" that this too effectively reduces to SR only formalism for all practical purposes (like I mentioned scientists do all the time as I described before?). All acceleration then being so reduced to insignificant effectiveness, then all motions of rod between train roof and floor could again be effectively treated as relative constant closing motions, not relative or absolute acceleration motions? Thankyou for answering and helping me think all these things through without being confusing like someone else I now know to take with a pinch of salt.
     
  8. Pete It's not rocket surgery Moderator

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    10,166
    One interesting thing about this scenario is that if the rod is straight before it is released in the train frame, then it won't be straight while it is falling, and vice-versa.
    The effect is very small for a short rod in normal gravity, but it's important if you want to properly consider what happens to the rod when the wires are cut, particularly in the platform reference frame.

    Let's say the rod is straight while it is falling. This means that when it is hanging from the wires, it must be slightly curved. The centre of the rod hangs lower than the ends. The ends of the rod pull upward on the centre to support it against gravity.

    When the wires are cut, the centre of the rod doesn't begin to fall immediately. It is still supported by the stress in the rod.
    The ends of the rod fall faster than g at first because the stress in the rod is pulling them downward. This is somewhat like the falling slinky effect, something everyone should try for themselves some time.

    So in the platform frame, when one wire is cut first the rod doesn't simply swing like a hinge from the other end... there is a wave of stress-release that travels along the rod.

    But, I still think that the bigger issue is that the shape of the rod is relativistically distorted, and that the effect of forces on the rod on the rod's proper shape need to be considered in the rod's rest frame.
     
  9. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

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    I think the issue here is not about force. We are measuring the distance and time of the fall of the rod (motion) in the train frame, not the force. For all we know the rod could be supported by a trap door, and when the trap door opens the rod falls. We want to know the DISTANCE the rod falls and the elapsed TIME of the fall. Once the distance and time is known the math begins.
     
  10. Pete It's not rocket surgery Moderator

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    10,166
    Yes I agree that distance and time are the key components.
    But in this scenario the rod/body is explicitly supported by two wires, not a trapdoor, and I think that the particular forces involved away from the centre of the rod are interesting.
     
  11. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

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    If you want to talk about different points on the rod, then you need to track the motion of every one of those points, closing speed, accelerations, velocities, distances, and times. There is no way out, Pete, All objects travel in the same frame.

    Edit: To make it a little more clear, you can talk about the earth's motion, or you can talk about the people on the earth's motion, or you can track the motion of the blood cells in those people, and all the while tracking the heart beat, the boat that just passed by, the airplane that just landed, and the moon that just fell below the horizon.
     
    Last edited: Apr 24, 2013
  12. Tach Banned Banned

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    5,265
    That has been explained to you, the fact that you don't get it is none of my concern.

    First you troll my posts and then you ask me to teach you? What a hypocrite.
     
  13. Undefined Banned Banned

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    No explanation so far except that rod falls in gravity acceleration as an "acceleration is absolute effect sense" and not "relative sense". Meanwhile relatively speaking the floor is "accelerating up" to meet the rod IF we consider the rod to be "stationary" and the floor "moving" relatively speaking. But the gravity well makes the rod the "preferrd frame" because it is NOT SR but GR which you say applies to rod motion absolutely not relatively. So no explanation except mixing of frames so far. That is all I have heard so far about your "train is an accelerated frame" assertion which you have not yet supported. How can you mix SR and GR like that and not explain yourself so you do not confuse me? Can you support it now so I can learn more than just your "lessons" on how to avoid answering questions when challenged to support your assertions? Please point to where I have "trolled your posts". I have been on topic and relevant and even you said I showed "excellent line of reasoning". Now all of a sudden you accuse me of "trolling". Unfair and not very mature, sir. Please do not do that again, thankyou.
     
  14. Tach Banned Banned

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    Please stop polluting the tread with your crackpot ideas.
     
  15. Undefined Banned Banned

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    1,695
    If you could just take the trouble to "pollute the tread" with an explanation to support what you meant I would be very grateful for such "pollution" instead of evasion.
     
  16. Tach Banned Banned

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    Since I wasn't answering (I told you I won't be giving you any more free lessons only to see that you are twisting my answers around) this isn't an "evasion". I was just pointing out that your post was pure crank stuff and I was asking you to stop polluting this thread with your fringe ideas, that is all.
     
  17. Fednis48 Registered Senior Member

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    725
    I agree that Tach is being a royal jerk here, but he's not mixing SR and GR. All three frames are subject to gravity. The rod is freefalling under gravity, so it is a rest frame. The train and platform are not freefalling under gravity, so they are accelerating frames.
     
  18. Tach Banned Banned

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    Wonder who the jerk is?

    Please Register or Log in to view the hidden image!

     
  19. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

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    Gravity present:

    Rod freefall and it's a rest frame, and the train is therefore the accelerated frame.

    or...it could be that the train is really free falling and the rest frame, and therefore the rod is the accelerated frame.

    Please Register or Log in to view the hidden image!



    One never knows without a preferred frame.
     
    Last edited: Apr 25, 2013
  20. Tach Banned Banned

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    Looks like you and Fednis48 are in agreement, must have gone to the same school. You two guys share a fixation with "rest" frames.

    That's a tough one, see if your buddy, Fednis48, can help you out again.
     
  21. Motor Daddy ☼☼☼☼☼☼☼☼☼☼☼ Valued Senior Member

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    5,105
    I was giving you a hint. You might need it.

    I mean, you promised to post your solution at the end, and I'm hoping that you thought this through thoroughly?? I mean REALLY thoroughly!
     

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