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I Friction in a simple mathematical pendulum

  1. Feb 14, 2019 at 3:26 AM #1

    MathematicalPhysicist

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    How do I guarantee that that the friction in the movement of a simple mathematical pendulum is negligible?
     
  2. jcsd
  3. Feb 14, 2019 at 3:38 AM #2

    BvU

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    Use a heavy weight, minimize air resistance, use diamonds for bearings, etc...
     
  4. Feb 14, 2019 at 3:58 AM #3

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    Heavy weight compared to the stand that the pendulum is situated on it, or something else?
     
  5. Feb 14, 2019 at 5:28 AM #4

    BvU

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    the air that has to be pushed aside for the pendulum to move. Can also be achieved by putting the whole thing in vacuo.

    To what purpose ? Saving energy, building a pepertuum mobile, verifying ##T=2\pi \sqrt{g\over l}##, other ?

    Familiar with the Reversible (Kater's) Pendulum ?
     
  6. Feb 14, 2019 at 5:37 AM #5

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    Verifying the formula.
     
  7. Feb 14, 2019 at 5:42 AM #6

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    The link you gave is for the physical pendulum, I referred to the mathematical point mass pendulum.

    I should have said that it's point mass.
     
  8. Feb 14, 2019 at 5:43 AM #7

    BvU

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    There's a good expression for ##T## with damping, so you can measure the damping by following the amplitude as a function of time (all pendula have damping) and correct ##T##. Depending on the accuracy of your measurements (in particular: L!), you can allow quite a bit of damping before such a correction becomes the main source of inaccuracy.
     
  9. Feb 14, 2019 at 5:45 AM #8

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    Do they exist ? What are you doing to verify this T formula ?
     
  10. Feb 14, 2019 at 5:46 AM #9

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    Nice thing about that one is that it is the exact equivalent of a mathematical pendulum.
     
  11. Feb 14, 2019 at 6:00 AM #10

    BvU

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    Don't see no point mass ...
    So you want to ask yourself:

    With what accuracy can I measure L and T
    Do I need to correct for damping ? How much damping is there ?
    What is the correction to T for the fact that this is a ball and not a point mass ?
     
  12. Feb 14, 2019 at 6:03 AM #11

    DrClaude

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    The post has been removed because it contained a picture in which some personal information could be seen.
     
  13. Feb 14, 2019 at 7:41 AM #12

    BvU

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    Only looked at the picture when it was still there.

    Way I meant it was that a ##\ \ \approx## 1 inch diameter metal ball is not a point mass.
     
  14. Feb 14, 2019 at 7:55 AM #13

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    So I guess it should work as a mathematical pendulum when the angle of release of the ball is small.

    How do I find the limits of small angles appropriate for a suitable mass?
     
  15. Feb 14, 2019 at 7:57 AM #14

    BvU

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    Experiment ! :smile:

    [edit] and of course, nowadays you also use your big brother friend google for a peek at the expression ... ##\qquad## :wink:
     
  16. Feb 14, 2019 at 8:02 AM #15

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    @BvU but can't I know from theory what to check for?
     
  17. Feb 14, 2019 at 8:03 AM #16

    BvU

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    was one step ahead of you :smile: see #14
     
  18. Feb 14, 2019 at 8:09 AM #17

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    Good to know there's big brother.

    I feel like there's no more need to work, everything is in the net nowadays :-D
     
  19. Feb 14, 2019 at 8:17 AM #18

    BvU

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    Yes, why bother trying to determine ##g## when you can also look it up ?:)
     
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