Recent Activity

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  Computation of G from Cavendish experiment

  I used original data from the Cavendish experiment to compute the value of G. My computation yielded a value for G 2.67 times greater than the recommended value:

  G(Cavendish) = 1.78424*10^-7 cm^3 sec^-2 g^-1

  G(recommended) = 6.67428*10^-8 cm^3 sec^-2 g^-1

  I used the well-known method of equating the torque of torsion wire (k theta) and the torque of gravity (GMmL/s^2) and solving for G:

  G = k theta s^2 / MmL

  k = torsion constant = 724.68 g cm^2 sec^-2
  theta = excursion angle from mid-point = 0.0054788 radians
  s = distance between weights = 21.97 cm
  M = big weight = 158100 g
  m = small weight = 729.8 g
  L = gyration arm = 93.09 cm

  More information about the geometry of the experiment can be found here. I would be grateful for any corrections and comments. Thank you.

  Posted 26 Aug 07

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  Moment of Inertia of the Cavendish pendulum

  I am trying to compute the moment of inertia of the Cavendish pendulum. I used

  I = 2(m r^2)

  r = gyration arm
  m = the weight attached to the pendulum

  But this formula is for a dumbell type of torsion pendulum where the weights are attached to the bar.

  Does anyone know the formula for the case where the weights are suspended as in the case of the Cavendish pendulum?

  With this formula I got

  I = 2 ( 729.8 * 93.1^2) = 12,651,243.56 g cm^2

  Does this sound right?

  Posted 18 Aug 07

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  Forces acting in Cavendish experiment

  In the Physics Forum Doc Al wrote that "there are two forces acting on the small masses: Torsion (kr) and gravity."

  Is this metaphorical type of speaking? How can the torsion of the wire can be said to act on the lead balls attached to the pendulum? I know that physicists use their own jargon. Maybe this is a statement that should not be taken literally?

  Posted 12 Aug 07

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  Experiment IV - Chart showing extreme points of the arm

  I just posted a chart showing the extreme points of the arm as measured by Cavendish 200 years ago today. Any comments?

  Posted 12 Aug 07

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  Occult does not exist in nature

  Newtonian force is occult. There is no occult in nature. Therefore force does not exist in nature. Therefore, Cavendish did not observe the occult force. Do you agree?

  Cavendish scandal

  Posted 07 Aug 07

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  Was Cavendish experiment a precise experiment?

  Not according to my definition of precise. Cavendish built his pendulum and placed it in a shed in his backyard. He then left it there for a year. During one year he made just 17 experiments. He calibrated the pendulum only once before he made his first measurement. During one year, the tension of the copper wire changed, the distances between weights changed. Cavendish ignored all these. What do you think. Are these signs of a precise experiment?

  Posted 05 Aug 07

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  Did Cavendish measure the Newtonian force?

  I don't think Cavendish measured the Newtonian force. I believe this can be proved either by analyzing his actual data and/or duplicating the experiment with a well-designed test. What do you think?

  Posted 02 Aug 07