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Value for gravity?

  1. Nov 5, 2003 #1
    Hi, new to here...

    I'm looking for the formula to determine accureate value of g when value of longitude and height above sea level are given.

    If you know if would be helpful if you could post a site that has the formula. (Want to have it as a reference).

    Thanx!
     
  2. jcsd
  3. Nov 5, 2003 #2

    chroot

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    Staff Emeritus
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    Gold Member

    I assume you mean latitude, not longitude. g varies with latitude because of the earth's rotation.

    Here's one page that may help:

    http://www.npl.co.uk/pressure/faqs/altgrav.html

    In general, you know Newton's law of universal gravitation:

    F = G M m / r^2

    and you know Newton's second law of motion:

    F = m a

    so you can substitute and solve for a:

    a (g) = G M / r^2

    Plug in the earth's mass for M and your distance from its center as r. Voila. This calculation, of course, does not include the small effect of the rotation.

    - Warren
     
  4. Nov 5, 2003 #3
    Do you want a theoretical prediction, assuming the Earth is a uniform rotating sphere, or do you want some kind of empirically-fit formula from measured data, taking into account all the irregularities in the Earth?

    (By the way, do you mean latitude, not longitude?)
     
  5. Nov 5, 2003 #4
    Oops you guys are right.

    Yep that's exactly the formula I'm looking for! Thanx for your help! :)
     
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