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Obit velocity vector variances, how it works?

  1. Feb 25, 2010 #1
    Why does the moon have a decelerated velocity on one half of its orbit and on the other side it has an accelerated velocity. And why is this same with the earth. From my data the variances in velocities of earth affect the velocity variance of the moon. So I have been able to create a formula of ware the hill of the ellipse of the moon will be, and it works. But I cant understand why this accurse. My train of thought directs away from Albert Einstein’s frame dragging and more towards Johannes Kepler. This is because of the velocity vectors and the affects on objects in a hill sphere.
  2. jcsd
  3. Feb 25, 2010 #2


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    Welcome to PF!

    Hi threadmark! Welcome to PF! :smile:

    Because the Moon is solid.

    If it was made of water, each molecule of water would be free (more or less) to follow its correct orbit.

    But all the molecules of our actual solid Moon are stuck together, and they all have to move with the same velocity … the velocity of the centre of mass.

    By contrast, the Earth is covered with water, and each molecule of that water (if we ignore currents and the rotation of the Earth :rolleyes:) does follow its own orbit … that's why the surface of the oceans are a different shape to the solid surface of the Earth (that shape has a special name, beginning with "geo", that I can't remember).​
  4. Feb 25, 2010 #3
    So density has something to do with it?
  5. Feb 25, 2010 #4


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    No. :confused:
  6. Feb 25, 2010 #5
    so its the centre of mass that bends space: ref from Rotational frame-dragging (the Lense-Thirring effect) appears in the general principle of relativity and similar theories in the vicinity of rotating massive objects. Albert Einstein's theory of general relativity predicts that rotating bodies drag spacetime around themselves in a phenomenon referred to as frame-dragging. so if its based on the principle of kr2 why is there an ellipse in the orbit and why doesn’t his formulas Eva consider velocities.
  7. Feb 25, 2010 #6


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    Sorry, you've completely lost me. :redface:

    This has nothing to do with relativity, it's just the definition of orbit.

    The effect would be the same if, for example, gravity was inverse cube instead of inverse square.
  8. Feb 25, 2010 #7
    I was under the impression that our hill sphere is round like a sphere, and that an orbit of mass is the only evidence of gravity? So I’m referring to the original basis for general relativity.
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