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Hole straight through the Earth?

  1. Jul 6, 2008 #1
    If a hole is somehow made to pass straight through the center of the Earth, and out on the opposite side, what would happen to an object dropped down the hole from one side?

    Would it stop and "hover" at the center? Or would it fall straight through to the other side, and than fall back again and again?
  2. jcsd
  3. Jul 6, 2008 #2
    It will oscillate back and forward because there is a kinetic energy involved.
  4. Jul 7, 2008 #3


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    The action is similar to a pendulum. It will slow down only through friction (air resistance).
  5. Jul 7, 2008 #4
  6. Jul 8, 2008 #5
    Oscillate back and forth through the center of the earth.
    What will happen is when it will reach the center, it will possess enough kinetic energy and will pass through the center.
    Then it will slow down, building Potential Energy and will stop after emerging at the other side.
    Then it will fall again, and the cycle will continue....

    Important assumptions made are.
    1)There is no air resistance.
    2)Earth is a perfect sphere.
    3)Mass is distributed homogeneously throughout the earth.

    All are actually false and the first two will start affecting the motion and will start opposing its motion, so that, each time it stops before emerging out the other surface and will start slowing down.
    This dampening will continue and after a huge amount of time, it will virtually stop at the center of the earth.
  7. Jul 9, 2008 #6
    If you work out the force on the dropped object as a function of its distance from the center of the earth, you will find that it is a linear relationship (i.e., F = k * x), so it would be simple harmonic motion (this is, of course, neglecting air resistance).
  8. Jul 9, 2008 #7


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    It will hit the Eastern wall of the hole.
  9. Jul 9, 2008 #8


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    Granted this is a thought experiment, but Lurch mentions a wrinkle that I'm surprised no one else has: the Earth rotates. In the ~90 minute passage of the dropped object, the Earth will have rotated 22.5 degrees. The object will collide with the wall of the tunnel.

    You'd have to do this experiment along the polar axis.
  10. Jul 9, 2008 #9
    lurch mentioned a good point....
  11. Jul 9, 2008 #10
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