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Special Relativity transformations

  1. Mar 11, 2014 #1
    1. The problem statement, all variables and given/known data
    A rod of rest length 1,0m is moving longitudinally on a smooth table with a velocity 0,8c relative to the table. A circular hole of rest diameter 1,0 m lies in its path. The diameter of the hole as seen by the rod is going to be larger?


    2. Relevant equations



    3. The attempt at a solution
    I guess no, because the length of a moving object relative to another at rest is smaller, from the contraction of length in relativity, but the asnwer is a larger length (1,667m). Why doest it happen?
     
    Last edited: Mar 11, 2014
  2. jcsd
  3. Mar 11, 2014 #2

    Doc Al

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    I'd say you were correct and the answer given is incorrect. Is this from a textbook?
     
  4. Mar 11, 2014 #3
    Thank you!
    Yes, it is from a textbook. From Resnick, Introduction to Relativity.
     
  5. Mar 11, 2014 #4

    rude man

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    I'd have to see a snapshot or scan to believe it. I agree with the OP and Doc.
     
  6. Mar 11, 2014 #5

    PAllen

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    I also agree with OP and Doc Al, and other posters. Further, this is a classic scenario in SR.

    What is true is that everyone agrees that the rod will hit the far edge of the hole. For the table frame, this is because the rod is smaller than the hole, and has a brief moment to fall so as to clip the edge of the hole. For the rod, the hole is small, but (using gravity as a force + SR) but moving upwards, bending the rod and hitting the edge of the rod.

    Note, you don't need any theory of matter or gravity to explain this. If you posit what happens in the table frame, a Lorentz transform to the Rod frame gives you all the rest (that he far side of hole and rod collide, that the rod bends, etc.).

    I also would like to see a scan of the text. I think it is more likely that OP is misinterpreting something than that a standard text like this can be in error on such a classic SR problem.
     
  7. Mar 11, 2014 #6

    TSny

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    I also wondered if such an error existed in Resnick's text. Wonder no more.
     

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    Last edited: Mar 11, 2014
  8. Mar 11, 2014 #7

    PAllen

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    Wow, the text is wrong and disagrees with its references. That is really shocking.
     
  9. Mar 11, 2014 #8
    The first book I used when I was self-learning SR was Resnick's text. In retrospect, I feel that it was awful.

    Chet
     
  10. Mar 11, 2014 #9
    Chestermiller, can you advise me a better book for the same subject?

    Thank you all guys for the support. It was really helpful. I'm learning by myself and I thought I had misunderstood. I appreciate. :)

    Greetings from Brazil.
     
  11. Mar 11, 2014 #10

    PAllen

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    See our textbook subforum! The following gets the most votes in that forum:

    https://www.physicsforums.com/showthread.php?t=665422

    (I can't say anything personally; I don't own it, and learned initially from a 1942 textbook; no, I'm not that old, just the book was).
     
  12. Mar 11, 2014 #11

    rude man

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    Quite amazing. Although I didn't use Resnick & Halliday for introductory physics in school I liked their book so much I went & bought it well after graduation - so this is indeed a shocker.

    We need to inform Dr. Resnick if we still can, don't know if he's still with Rensselaer Poly.

    Or maybe this is his son or ...? (The Resnick of R&H is Robert Resnick. PAllen, what's the name in your SR text?).
     
  13. Mar 11, 2014 #12

    PAllen

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    It was Bergmann's classic on SR and GR. I worked through every problem in it in high school with no one available to help.
     
  14. Mar 12, 2014 #13
    I understand Resnick has passed on in late January. He will be missed. I am surprised I have not seen this mentioned in any physics forum columns.
     
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