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Moonrock gravitationally same as earthrock?

  1. Nov 10, 2006 #1
    To test the hypothesis that moonrock is gravitationally attracted to the moon slightly more than is earthrock one could measure the deviations of a balance scale weighing NASA-provided moonrock against an equal (earth) weight of (say) granitedust from horizontal during a lunar orbit cycle and compare this to the deviations of the balance when the scale is balanced by two equal weights of granitedust.

    I remember reading somewhere that this or a similar experiment has been done and proven negative (consistant with G being the same for all matter) but can't now find the details.

    Can anybody help? TIA.
  2. jcsd
  3. Nov 10, 2006 #2


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    What is the basis for your reasoning?
  4. Nov 10, 2006 #3
    In the case of weighing to equal weights of granitedust, as the moons orbit passes nearer the scales it will have a very slight unbalancing effect on it, the moon always being slightly nearer one end than the other unless the scales are psotioned extremely carfully with regard to the lunar orbit. But if one of the wieghts is moonrock that is hypotheised more attracted to the moon than is granite, the imbalance will be more pronounced.

    But I'm not sure how my "reasoning" is relevant. Its an obvious experiment which I think has been conducted.
  5. Nov 10, 2006 #4

    Chi Meson

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    The Moon is 360,000,000 meters away. It's Mass is 7 x 10^22 kg. Here at the earth,the moon pulls on a 1 kg rock with a strength of 4x10^-5 N, which is 0.000008 lbs of force.

    Your experiment requires finding the difference between the forces on moon rock and earth rock, which (even if plausible) would be a tiny fraction of this tiny amount. Balance scales do not have this kind of precision. A "null" result is one that is inconclusive as this experiment would be.

    Contrary to your description, the difference in pull would be maximized when the moon is straight overhead above the scale (unless the scale has balance pans hundreds of kilometers apart).

    I have never heard of this speculation nor this experiment. I don't think NASA would have bothered to carry it out. Sounds like someone's "thought experiment" to me. Other tests have proven conclusively that mass will not attract differently to different bodies.
  6. Nov 10, 2006 #5
    Disturbances due to different moonrock/earthrock attractions yes. Deviations due to the moon imbalancing the earthrock/earthrock balance no.

    Can you give details please?
  7. Nov 10, 2006 #6


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    Why do you think there would be a difference?

    Earthrock and Moonrock are made of the same stuff.
    Even the original source of both is the same.

    Try looking up Etovos experiments.
  8. Nov 10, 2006 #7
    Why would they be the same? If I took two pieces of iron from different parts of the earth's core, and took two cubic centimeter cubes from one and one from the other I would expect the forces between the two "neighbour" cubes to be different to that between distant sourced cubes because the ferromagnetic homogeniety are likely to differ. You might argue that thats electromagnetism rather than gravity but as I suspect
    gravity to be an artifact of electromagenetism thats not an effective rejoinder. Then there is the question of fluidity. I would expect granitedust to be more attracted to the moon than granite because the lunar pull would draw the dust toward the moon slightly, dehomegenising its density in favour of the attraction. There is the possibility of quantum entanglements persisting between seperated objects, and also the possibility of resonance effects between distant but similar atomic arrangements.

    Yes, but there has been a seperation; possibly according to kind.

    Ah yes, thanks.
  9. Nov 10, 2006 #8

    Chi Meson

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    I have no idea what you think you are talking about.

    Oh, I get it now. Goodbye.

    This thread will probably be locked soon.
  10. Nov 11, 2006 #9


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    I agree that the experiment you describe would show any difference between the gravitational attraction of the Earthrock to the Moon and that of a Moonrock, if equipment sensitive enough to take such a measurement exists (I think that it may).

    However, I've never heard of anyone performing such an experiment. I would expect the average scientist (who would be expecting a negative result) to be unwilling to waste the time since, upon recording a negative result, he would only find his result challenged by those who say the difference was there, but too subtle to be recorded by current equipment.

    You seem to believe that a difference does exist. Do you know others who share this belief? They would be the ones to attempt such a measurement, since they would be expecting a positive result (and just one verifiable positive result would prove the point).
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