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Homework Help: Total tension in wire due to bird

  1. Oct 21, 2009 #1
    1. The problem statement, all variables and given/known data
    I have a conceptual question related to the exact problem in this thread: https://www.physicsforums.com/showthread.php?t=125801

    2. Relevant equations

    Same as in this thread: https://www.physicsforums.com/showthread.php?t=125801

    3. The attempt at a solution

    My question is why is the total tension 613 N? If you try and solve T1 = 9.81/(2sin(tan-1(0.200/25.0))), you get T1 = 613 N. However, T1 = T2. So wouldn't the total tension in the wire be 1,230 N (after rounding due to significant figures)? Could someone please explain this to me?
  2. jcsd
  3. Oct 21, 2009 #2


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    Hi Subdot! :wink:

    The question asked "How much tension does the bird produce in the wire?" …

    on the left, there is 613 N, and on the right there is 613 N …

    so the tension in the wire is 613 N. :smile:
  4. Oct 21, 2009 #3
    Hi! And so if I understand you right, "total tension" (which would be the total force the wire exerted on the bird, I guess) is not the same as just plain "tension" in a wire?

    Out of curiosity, what would happen if the bird was not in the middle of the wire? How would you determine the amount of tension the bird causes in the wire then? Or would the tensions on either side of the bird still be the same?
  5. Oct 21, 2009 #4


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    I've never heard of "total tension" …

    it's not in the original question …

    where did you get it from?​
    Tension in a continuous rope is the same all the way along.

    Where it touches something, the tensions will still be the same on both sides provided there's no sideways force at that point, which in practice means no friction.

    For example, most exam questions talk of "frictionless pulleys", because then the tension will be the same on each side of the pulley.

    In the case of the bird, I think a lot depends on exactly how the bird attaches itself to the rope: that's why the question put the bird exactly half-way, so that it didn't matter. :wink:
  6. Oct 21, 2009 #5
    Oh, I get it now. Thanks for the help! And "total tension" is a word I threw in there meaning the equivalent of "total force" acting on the bird from the wire. I probably got the word from the process of solving another problem involving tension.
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