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Thread: Earth-Moon Barycentre

  1. #1 Earth-Moon Barycentre 
    The Doctor Quantime's Avatar
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    If the earth and the moon orbit the barycenter that is a few thousand kilometers under the earths surface pointing towards the moon at all times then my question is this:

    Why are all objects on earth pulled down towards the centre of the earth? And not the barycenter? Is there a difference between orbital gravity and gravity in general? Or am I confusing this with something else.

    Thanks guys! :-)


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    Comet Dust Collector Moderator
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    Use the gravitational formula, and you will see that for someone on the surface, the earth's mass is almost all of the gravity. Technically, you do weigh a hair less when the moon is overhead, but the amount is extremely small, too small to easily measure.


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    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by Quantime View Post
    If the earth and the moon orbit the barycenter that is a few thousand kilometers under the earths surface pointing towards the moon at all times then my question is this:

    Why are all objects on earth pulled down towards the centre of the earth? And not the barycenter? Is there a difference between orbital gravity and gravity in general? Or am I confusing this with something else.

    Thanks guys! :-)

    The barycenter is the "balance point" between the Earth and Moon. One way to look at it is that if the Earth and Moon were sitting on a see-saw, the barycenter is where you would have to put the fulcrum is order for them to balance. While for something that is far removed from the Earth-moon system (like the Sun) it behaves like the gravitational center of the Earth-Moon system, once you get closer in, the "lumpiness" of the system caused by the fact that the Earth and Moon are separate masses begins to dominate.
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    The Doctor Quantime's Avatar
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    Thank you very much guys very clear
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