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Forces on a string applied perpendicular / tangent direction

  1. Sep 3, 2014 #1
    Hello guys,

    I've had the following discussion at work:

    We are currently using a suture with a nylon thread on a tissue, when the thread of the suture is tightened in a force equal to if we've put a 500 gram weight on both ends of the suture line (meaning both end are tied together to the weight).
    The assumption is that in this mode, the tissue will fail with a load higher than that.

    We were wondering, if the force was applied perpendicularly (direction of the screen) would the max wight change from 500 gram to another value?

    Would love a direction to some equations to rationalize my first instinct of saying "No!" :-)


  2. jcsd
  3. Sep 3, 2014 #2

    Simon Bridge

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    It does not matter which direction the force is applied - a 500g-force is a 500g-force.
    The effect this has on the suture/tissue may be different at different angles.

    Note: two ends tied and attached to 500g - each thread has to support 250g + whatever lateral forces are produced by pulling on the tissue. That's something like 250g tension in the thread.

    Your diagram has a total of 500g-force applied at three places on the thread ... So each attachment point is supporting 500/3 g-force ... and each is basically the same as two ends, so the tension in the thread is 500/6 g-force.

    S the answer kinda depends on the specifics of the question you want to ask.
  4. Sep 4, 2014 #3
    Hi, thanks.
    Yes I recon it depends on things like the length of the suture, its width, angles and so on.
    But assuming both are identical for the two cases, the tension of the suture would still be 500/6 even if we apply it in at the direction of the screen instead of "pulling it" like in pic 1 (?)
  5. Sep 4, 2014 #4

    Simon Bridge

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    In one pic the weight is applied to only one location in the loop - in the other pic the force is applied to three locations at the same time - if I read that right. That's what makes the biggest difference since it's the same total force.
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