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Homework Help: A Pendulum

  1. Nov 22, 2005 #1
    Could someone please explian the motion of a pendulum for me? When the weight is heavier is the pendulum slower or fast than when the weight is less?
  2. jcsd
  3. Nov 22, 2005 #2


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    Could you brief a bit more on your current physics background or at what level are you studying harmonic motion.

    The equation for the period of a pendulum is

    [tex] T = 2\pi \sqrt{\frac{L}{g}}[/tex]

    where L is the length of the pendulum and g is the gravitational constant. As you can see, there is no mass in the equation.
  4. Nov 22, 2005 #3
    I am teaching myself Physics 20. the question is basically that you tie a cococnut to a string and put a hole of the cocnut at the bottom so that the milk flows gradually out.

    The question is asking what variables affect the period of the penduallum
  5. Nov 22, 2005 #4
    A screw is put into the top of a cocnut and a long string is tied to the cocounut to make a simple penullum. A small hole is punched into the bottom of the coconut and the pendulum is made to oscillate. The cocnut milk flows gradually out through the hole. It is observed that the period gradually increases at first and then gradually decrease to its initial value. Explain why the period of the pendulum changes in this way.
  6. Nov 22, 2005 #5


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    As mass in the pendulum decreases, so does the force of gravity on it. So while it can now move faster due to less inertial resistance, there is less force making it move. The trade off is just enough so that mass doesn't affect the speed of the pendulum. Only the variables mentioned will.

    Edit: Are effects of air resistance involved?
    Last edited: Nov 22, 2005
  7. Nov 22, 2005 #6
    I don't know
  8. Nov 22, 2005 #7
    part A askes Which variable(s) affect the period of the pendulum
  9. Nov 23, 2005 #8
    As the earth doesn't care how massive an object is when one leaves two bodies with different masses they fall with the same g=9.81
    so is with a pendulum as they release from their maximum height ,they won't become affected by their masses.
    But if you connect some mass with a spring and
    you make a mass-spring system ,the mass does
    influence the motion of the spring.For a large mass the vibration of the spring becomes slower.So one may find the value of a mass on some planet by a mass-spring system .
    One can measure the g-value for an unknown planet through a pendulum.
    much luck
  10. Nov 27, 2005 #9
    there is more tension in the string while the coconut contains liquid, Tension = W = mg
    stretching the string, thus increasing L, increasing T

    the swaying of the liquid (momentum; mv) inside the coconut will add a marginal horizontal force pushing the coconut higher and decreasing the frequency (f = 1 / T) of oscillation.
    thus increasing T
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