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Does every orbiting object have spin

  1. Jan 24, 2016 #1
    Our moon rotates around Earth in such a way that we always see the same face. But Earth orbits Sun in a different way. It keeps spinning. My question is, If I were to go to space and put a basketball in a circular orbit around earth in such a way that at the time I throw it a particular face is facing Earth would it orbit Earth like the moon does(always the same face) or would it have a much faster spin?
     
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  3. Jan 24, 2016 #2

    BvU

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    No coincidence, but the ultimate result of tidal deformation.

    Your baseball would spin at whatever spin rate you give it when throwing. If you throw exactly hard enough for a circular orbit and don't give it any spin, it wouldn't rotate, just orbit. (i.e. on your location on earth you always see the same side, but your antipodes see the opposite side). In the long run this tidal deformation might change that -- see link.

    Think of the central character of the gravitational force and conservation of angular momentum.
     
  4. Jan 24, 2016 #3
    Thanks for your answer. Just clear one more thing .. Just to confirm If I have properly understood what you're saying...
    If instead of a baseball I use a physical arrow .. throwing it hard but no spin at all .. is it true that in its circular orbit there will come a time when the arrow will be parallel to the surface of the earth and there will also come a time when it will be perpendicular?
    And if this is true then why is it that whenever we see pictures of artificial satellites like ISS orbiting earth .. their main body seems parallel to the surface of earth? Do they add spin when they launch it?

    P.S: The arrow thing will only be true if velocity vector is parallel to the body of the arrow .. If it is perpendicular then it will always remain parallel to earth. And the same might be true with ISS. Looking forward to your reply!
     
  5. Jan 24, 2016 #4

    BvU

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    The consequence of what I wrote would indeed be as you describe: orientation in space invariant, so wrt earth center it will rotate once per orbit.
    ISS and other earth-facing satellites will probably be oriented properly with small steering jets.

    @haruspex: are you aware of any mechanisms that would be helpful (or unhelpful) in this ?
     
  6. Jan 24, 2016 #5
    Hmm.... Thank You
     
  7. Jan 24, 2016 #6

    haruspex

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    I agree with what you posted. All objects would be subject to some tidal deformation, and over time that would lead to tidal locking.
    Some satellites would be set into a one spin per orbit mode deliberately, so tidally locked from the start. Others might need to be in constant sidereal orientation, so might need a very small jet to maintain that. But without doing the calculation, I would guess the effect is small compared with, e.g., the solar wind on the solar panels.
     
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