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Homework Help: Is a spring longer hanging or flat on a table?

  1. Oct 12, 2011 #1
    1. The problem statement, all variables and given/known data

    Is a spring longer hanging or flat on a table?

    2. Relevant equations
    logic.


    3. The attempt at a solution

    I think the answer would be hanging because then the mass of the spring pulls it down a bit, thus stretching it more than when it is flat.
     
  2. jcsd
  3. Oct 12, 2011 #2

    256bits

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    Gold Member

    Re: Springs

    I would agree.
    A good example of the type of spring we are talking about is a slinky toy.
     
  4. Oct 13, 2011 #3
    Re: Springs

    But how do I write it using math/formulas.
     
  5. Oct 13, 2011 #4
    Re: Springs

    It would be difficult to do that, because the spring must be considered massive, and hence will have different tensions at different points.

    But I guess you can prove it if you make an assumption that if any point in the spring has tension, then it is possible only if it is elongated.

    Now just divide the spring into two parts, and draw the free body diagram of the bottom part. Now prove that a certain tension must exist at the join point, to keep the bottom part of the spring in equilibrium.
     
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