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Why do stars and galaxies spin?

  1. Dec 17, 2008 #1
    It takes a continuous input of energy to spin, otherwise things would fly apart or stop spinning. So why do large macro objects spin, and continue to spin?
  2. jcsd
  3. Dec 17, 2008 #2
    Ever heard of angular momentum?
  4. Dec 17, 2008 #3
    Consider the following situation. A spinning globe of pure ice, say a small meteor, a meter in diameter, spinning around its own axis, approaching the sun, so that as it approaches the sun, it melts. Are you saying that the globe of ice will continue to remain a globe of water, still a meter in diameter, even after it melts?
  5. Dec 17, 2008 #4


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    Yes and it will still spin with the same angular momentum
  6. Dec 17, 2008 #5

    Vanadium 50

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    There's your problem right there. It doesn't. Unless an external torque is applied, once an object starts spinning, it stays spinning.
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