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Differential gravitational force causing tides model?

  1. Jan 25, 2015 #1
    1. The problem statement, all variables and given/known data
    upload_2015-1-25_16-6-47.png

    2. Relevant equations


    3. The attempt at a solution
    For a), I initially tried to consider the component of the gravitational force of the moon acting normally to the earth's surface. This would be F=F_0 cos(theta) where theta is the angle between a horizontal line going through A and B and the point on the earth's surface in question (giving zero at the poles and maximum at the equator). I know that , due to the effect of the Earth actually undergoing circular motion and 'free-falling' due to the moon's gravitational pull, the force at each point on the side of the Earth facing the moon will be (approximately) mirrored by the opposite side of the earth since r<<x. But now I am stuck. I wanted to deal with forces rather than equipotentials, as it seems like the question wants you to just deal with the forces. I was considering the fact that the effect is actually spherically symmetrical when looking onto the face of the Earth from the moon, but II don't know what to do with this to find the heights? I could find the total volume of water on the Earth by doing surface area of earth x 750, but I still don't see how II could use this?


    Thank you in advance :)
     
  2. jcsd
  3. Jan 25, 2015 #2

    mfb

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    Staff: Mentor

    I don't see why. Potentials are fine.
     
  4. Jan 25, 2015 #3
    Help! I cannot figure out how to get the equation with the equipotential. Would I have to consider the earth's rotation? And how to I create a potential due to the moon?
     
  5. Jan 25, 2015 #4

    mfb

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    In the same way you do for earth, with Newton's law of gravity.
    Not the 24h-rotation, but the motion around the center of mass of the earth/moon system is relevant to get the second tidal wave at the opposite side.
     
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