Why does the world spin?

  1. What makes the world spin?
  2. jcsd
  3. Bandersnatch

    Bandersnatch 1,398
    Gold Member

    Hello, mrblint.

    Why won't you tell us what do you think it is, so we know where to start explaining?
  4. I think that as the world travels around the sun in an elliptical orbit, there is a force pulling away from the sun (the centrifugal force) and also the sun is also pulling the mass of the earth towards itself (the sun being the more massive body). As the earth moves in the elliptical orbit, the slightly changing orientation of the pull results in spin of the planet on its axis. That's what comes to mind just thinking about it. But I'm wondering now if the earth spins at different speeds as it moves through the elliptical orbit.
  5. Yes. The speed increases as earth gets closer to the Sun. The orbit is only very slightly elliptical though so it's not a big change.
  6. The reason the world spins on its axis has to do with the conservation of angular momentum.

    As the dust gathered that formed our planet the dust collisions imparted inertia. As the diameter decreased the angular momentum increases much like a spinning figure skater.
    Nearby large gravitational bodies can affect the spin in a fashion called "tidally locked"
  7. Correct. May I add that it would be extremely unlikely to have a huge primordial dust cloud with a very small or zero angular momentum. So the rotation of the entire solar system was pretty much there since it formed. Otherwise one would expect the whole thing collapses in one blob point without rotation. As far as I know, all planets move in the same direction in the disc around the sun and the sun itself rotates in that direction. There are, as far as I know, only a few captured moons for the big planets that rotate in other ways, and there is just one "misbehaved" planet, Uranus, where the axis of rotation is almost parallel to the planetary disk. (Well, Uranus also got a weird name, at least in English ;-).

    I still wonder though if there are any planetary systems out there where all this isn't the case, and where the planets are not just in one disk but varying planes of their orbits - and then why that could be?
  8. Planets that have been thrown out of their original systems and hurtle through space and end up in other systems could be such cases. Among the gazilions of stars there surely must be numerous examples of such planets.
  9. HallsofIvy

    HallsofIvy 40,678
    Staff Emeritus
    Science Advisor

    I thought love made the world go around!
  10. if its any consolation it will still make your head spin lol
  11. Bandersnatch

    Bandersnatch 1,398
    Gold Member

  12. Roflmao now there is a correlation I never would have thought of lol
  13. Could be, but it probably wouldn't last long. The mutual interactions between the planets in all of those strange orbits would tend to either kick some of them out of the system or settle them into one plane.
  14. HallsofIvy

    HallsofIvy 40,678
    Staff Emeritus
    Science Advisor

    Would you really consider it "natural" if the world happened to have exactly 0 angular momentum?
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