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Objectively measuring gravity

  1. Jun 22, 2015 #1
    Of course our gravitational relationship with the Sun and our own Moon are understood, but to what extent can we measure even the faintest attraction with other bodies in the Solar System.

    How do Mars, Venus and Jupiter effect Earth?

    Do we have Barycenters with these bodies and others more remote?
  2. jcsd
  3. Jun 22, 2015 #2


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    Have you tried to calculate the gravitational force between Jupiter and the earth? Perhaps compared it to the moon and the earth? The mass of Jupiter and the distance can be found online.
  4. Jun 22, 2015 #3
    When a third source of gravity is added and calculated for, the whole system's motions become really complicated. Usually, a computer is used to make such calculations. But sometimes, if the third object is really tiny or far away, it can be ignored, and the trajectories can still be reliably predicted and followed.

    Most planets have an insignificant impact on earth's trajectory, even Jupiter, but they can still be calculated.
  5. Jun 22, 2015 #4


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    We can't really directly measure the force. Instead, one way we can see the effect is to build a model using the laws of physics and compare our model to the motion of the Earth, Moon, and other bodies. If our model accurately matches our observations, we can say our model is a good model that accurately describes the interaction between the bodies within the limits of the model. We can then manipulate this model and see what happens when we take out Jupiter or Saturn or another body. Comparing the two scenarios tells us the effect those bodies have on us.

    In essence, our 'measurement' uses the motion of the planets themselves over a long period of time.
  6. Jun 23, 2015 #5

    Thank you
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