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From where did our earth get its initial velocity ?

  1. Mar 20, 2013 #1
    I read in a article that earth revolves around the sun at speed of 30km/s but from where did it get its velocity at the beginning..?
  2. jcsd
  3. Mar 20, 2013 #2


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    From the conservation of the angular momentum.

    As the interstellar cloud of gas collapses to form a protoplanetary disk, random motions of the molecules do not perfectly cancel out, causing the emergence of a preferred spin direction in the macroscale. Further collapse exaggerates this initial preferrence, as any initial angular momentum has to be conserved in a closed system.
    This is also the reason why all planets revolve around the sun in the same direction, and have generally the same direction of rotation on their axes.
    Although in that last case there's obviously more at play than that. Just look at Venus or Uranus.
  4. Mar 20, 2013 #3
    @Bandersnatch :

    But how that could account into the revolution of planets.. its something related with the rotation of the planet.. how is it related with the revolution..?? thats the part i cant understand..
  5. Mar 20, 2013 #4


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    I'm not sure where lies your confusion. It's the same mechanism. Only instead of the scale of a single planet it's the whole solar system.

    Here's a video showing the simulation of the process:

    and the paper from which it's sourced:
    Last edited by a moderator: Sep 25, 2014
  6. Mar 20, 2013 #5


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    Your question implies that you think it is strange that the rotation is not exactly 0. Wouldn't it be more strange for the rotation to be exactly a predetermined number, like 0?
  7. Mar 20, 2013 #6
    The material the earth is made of was flying around in space. Dust and gas has some random movement, something had pushed it a little etc or it just happened to move some way since the last place it came from. When it starts collecting toward some center, it is likely that it has some small net rotation around the center, ie it is not likely that for every piece of dust going one way there is one going the other way, there is some imbalance. The falling towards the center makes them speed up and the effect gets exaggerated. You may be aware of the skater speeding up when the arms are pulled in effect, which also happens with the collapsing dust.
  8. Mar 21, 2013 #7
    yup.. now i got it.. pls stay tuned for further questions..
  9. Mar 22, 2013 #8
    If you want to go back even further, the ultimate source for any momentum of any particle is, of course, whatever caused the big bang.
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