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Trying to understand basic gravitation

  1. May 13, 2012 #1
    I have a bit of intuition on microscopic structures, so I "easily" understand things such as chemistry, nuclear and particle physics and the such. I'm no expert in these subject or anything but I do have a easier time learning it.

    But I REALLY have a hard time understanding some macroscopical/astronomical structures.
    But I intend to fix it.

    Anyways, what I still don't understand about gravity is the circular/elliptical orbits of planets/satellites/stars/etc. This question might sound silly but...

    Why don't the moon just falls on Earth? I understand it is constantly "falling" towards the Earth and all. What I mean is, why does it have a horizontal component of velocity which makes it "not really fall"? Is it because it had a initial velocity different than zero? Does it depends on the initial conditions of the system or something like that?
  2. jcsd
  3. May 13, 2012 #2


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    Hi U.Renko! :smile:
    Yup, that's exactly it! :biggrin:

    Anything that's orbiting anything else is doing so only because the initial conditions were right.

    (Having said that, the formation of the Moon is actually a bit of a mystery … very likely, it happened when a proto-Moon in the same orbit as Earth "backed into" Earth … I suppose it must have done it with "sidespin", or the debris would just have gone straight up and down again?! :confused:)
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