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Tension in the toy string

  1. Mar 27, 2008 #1
    we hung a toy pig from the ceiling with a string and when turned on, it travelled in a circle.
    We figured out the tension in the string using dynamic and static method...
    in dynamic we just used the measured radius and found out the angle to calculate the force of tension.
    in static, we measured the horizontal force by attaching the spring scale's hook to the hook where the string was hooked on. We pulled the apparatus horizontally to the radius. With this and the angle we calculated the force of tension.

    My question is...
    What is the difference in the result of the two methods?
    Why is one called dynamic and the other, static?
    Why do I get a slightly different tensions for the two methods?? What's the cause of the discrepancy?

    Any help would be appreciated. :)
     
  2. jcsd
  3. Mar 28, 2008 #2

    tiny-tim

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    Hi ys2050 :smile:

    I love your flying pig! :smile:

    (Did you ever work out why it wouldn't go backwards?)

    Can you tell those of us who haven't seen it:

    What do you mean by "turned it on" - where is the motor, and what does it do?

    In the static case, I'm not getting it … what position did you pull the pig to, and what connection does that have to the dynamic case? :smile:
     
  4. Mar 28, 2008 #3
  5. Mar 28, 2008 #4

    tiny-tim

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    … just like in nature …

    Thanx, acolavin! :smile:

    ooh … I see it "has a realistic flying motion" …

    hmm … how do they know? :smile:
     
  6. Mar 28, 2008 #5
    I pulled the pig horizontally to its radius and the spring scale showed the horizontal force. I used that and the angle to figure out the tension of the string, which is the hypotenuse.
    In the dynamic method, I used the formula T = mg / cos(theta)
    In the static method, I used T = Fc / sin(theta), where Fc is the horizontal force.
    and no... i still don't know why it can only fly in one way...
     
  7. Mar 28, 2008 #6

    stewartcs

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    No, the spring scale will show the tension in the string, not the horizontal componet.

    CS
     
  8. Mar 28, 2008 #7

    but in the handout, it says:
    " Holding the other end of the spring scale, horizontally pull it out to its radius when it was flying around in a circle. Note this reading down and calculate the tension in the string."

    If the spring scale does measure the tension of the string, why would you need to do any calculation?!?!?!
     
  9. Mar 28, 2008 #8

    stewartcs

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    If you pull on a string that is connected to a spring scale that is fixed to an articulated point, then the reading on the scale at that moment is the tension in the string.

    However, I misunderstood what you were looking for. I believe that you are looking for the tension in the string the moment the pig was flying and trying to calculate it based on the tension you just measured in the horizontal direction while pulling the pig out to the radius of flight...right?

    CS
     
    Last edited: Mar 29, 2008
  10. Mar 29, 2008 #9

    tiny-tim

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    … spring horizontal … ?

    Ah, but I think ys2050 is holding the spring horizontally, so as not to interfere with the vertical component of the tension (so that it still matches the weight of the pig).

    He therefore does measure only the horizontal component of the tension, and has to make a calculation to get the full tension.

    Is that right, ys2050? :smile:
     
  11. Mar 29, 2008 #10

    stewartcs

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    That's what I just said.

    CS
     
  12. Mar 29, 2008 #11

    Doc Al

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    I think your previous response could be misinterpreted.
    In the "static" case, the spring scale is attached to the pig, not the string on which the pig is hanging. So the scale reading is not the tension in the string (at least not that string).
     
  13. Mar 29, 2008 #12

    stewartcs

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    Sorry, I thought I had made that clear by not mentioning a pig anywhere in the system.

    The way I interpreted the measurement method was that the pig was removed and the spring scale was attached to the ceiling hook, then a string was attached to the spring scale and pulled to the radius of where the pig was flying.

    I can't believe I'm talking about flying pigs. :rofl:

    CS
     
  14. Mar 29, 2008 #13

    Doc Al

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    Perhaps it wasn't clear from this thread (he has another thread on the same topic :mad:), but he's measuring the same tension via two different methods. In both methods, the pig is there.
    You've got to believe!
    [​IMG]
     
  15. Mar 29, 2008 #14

    tiny-tim

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    … ooh look … there's another one … !

    A flying pig without the pig … is like a grin without the cheshire cat! :biggrin:

    Never ignore the flying pig!

    Those who ignore flying pigs …

    :rofl: are pig-ignorant! :rofl:​
    Would you believe … they're talking about you? :smile:
     
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