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Question about the Earth and Constant Angular Momentum

  1. Feb 27, 2010 #1


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    The Earth is rotating because of constant angular momentum, right?

    Would I be correct in interpreting that this is because the Earth's tilt is at an angle of 23.5 degrees, and so this angle is what causes it to keep spinning?

    Is it possible to replicate constant angular momentum? And, to put it into comparison, would a good way of putting it be to think about a swing in a park that swings 360 degrees around the bar, then continues to swing 360 degrees forever?

    If constant angular momentum holds true for the Earth, does that mean that the Earth will ALWAYS orbit at its velocity?


    EDIT: I just read that the axial tilt of Mercury is 0 degrees (no tilt). So how does the constant angular momentum work?
  2. jcsd
  3. Feb 27, 2010 #2
    Why do you think that the tilt makes a difference?
  4. Feb 27, 2010 #3


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    because it says constant *angular* momentum... am I interpreting it wrong?
  5. Feb 27, 2010 #4


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    Well, the fact that the Earth is rotating and the fact that the Earth has angular momentum are two ways of saying the same thing.

    For comparison: if an object has a velocity, and no force acts upon it, then the velocity will remain the same. This can equivalently be phrased as follows: when no force acts upon an object the linear momentum is constant.

    Being equivalent statements either one implies the other; that is the relation between the two.

    There's no connection with the concept of causal relation; it makes no sense to say something like 'the constant angular momentum causes the velocity to remain the same.'
  6. Feb 27, 2010 #5


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    Angular momentum is around the axis of rotation. The tilt is of the axis of rotation. They are unrelated.
  7. Feb 28, 2010 #6
    Yes the tilt is apart of the angular momentum, and I will explain why. There is a theory that the moon came from earth because of a massive collision around the birth of our earth. The collision created our moon and also over time the earths axis was manipulated by the orbit of the moon or in the initial collision. In order to keeps its angular momentum the axis is tilted to keep the balance between the two being orbit vector of the moon and the rotation of the earth. If the tilt wasn’t present the orbit vector of the moon being on an angle, would not maintain an equal orbit to the hill sphere. So the angle of earth is crucial for the orbit vector to maintain its trajectory with a moon with an orbit such as the one earth has.
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