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Homework Help: Finding The Momentum Of Earth

  1. Dec 9, 2012 #1
    The problem is:

    "Model the Earth as a uniform sphere. Calculate the angular momentum of the Earth due to its spinning motion about its axis."

    So, I first pointed out the the earth rotates about its axis in 24 hrs x 3600 s / 1 hrs = 86400 s

    Then I noted that a fixed point on the earth rotates through a angle of 2pi, tracing out the circumference of the earth, in 86400s: [itex]\omega=\frac{2\pi}{86400s}=7.27\cdot 10^{-5}[/itex]

    The rotational inertia of the sphere being [itex]I=2/3MR^2[/itex]

    Angular momentum being [itex]L=(2/3)(5.97\cdot 10^{24})(6.37\cdot 10^6)^2(7.27\cdot 10^{-5}=1.17\cdot 10^{34} kg\cdot m^2/s[/itex] However, this answer is wrong. What did do wrong?
  2. jcsd
  3. Dec 9, 2012 #2


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    You've used the wrong moment of inertia. (Hint: is the earth solid or hollow?)
  4. Dec 9, 2012 #3
    Hmm, it certainly isn't hollow. Thank you very much for the help.
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