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Variations in the strength of gravity throughout the earth

  1. Apr 27, 2012 #1
    Which parts of the earth is gravity stronger than usual, at higher points on the earth is the gravity stronger or weaker than the lower points and why?
     
  2. jcsd
  3. Apr 27, 2012 #2

    tiny-tim

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  4. Apr 27, 2012 #3
    As a contributer to physics forums and a teacher interested in hearing the opinions of others can I say that it is very disappointing to find a query being directed straight to Wikipedia.
    I thought this was against the standards expected here.
     
  5. Apr 27, 2012 #4

    phinds

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    I think the "standards expected here" are that folks will make some attempt to do their on at least modest research before asking questions that such modest research would answer.

    It is QUITE common (and I think absolutely appropriate) in such situations to point someone to something they could have found on their own with little or no effort.
     
  6. Apr 27, 2012 #5

    D H

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    You're right. tiny_tim's answer wasn't quite appropriate. He should have answered "This sure looks like a homework question. What do you think? What have you found on your own to answer this question?"
     
  7. Apr 27, 2012 #6

    haruspex

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    I agree completely, phinds. Too many questions posted on this Forum could have been answered quite easily by a little research. Where a Wikipedia or similar entry was found, but the questioner still does not understand, the ideal would be for the questioner to cite the found reference, identifying where possible the exact place where puzzlement arises. That would avoid a lot of to-and-fro where the questioner supplies insufficient information or a reference to some obscure textbook.

    Where such preliminary research has not been done, replying on this forum by link to a good reference is an excellent response. It shows the questioner appropriate methods for getting a rapid resolution and, probably, a more authoritative answer.
     
  8. Jul 20, 2012 #7

    Evo

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    If a source exists that contains accurate information, it is very appropriate to refer someone instead of re-typing all of the information. Why re-create the wheel? Also, tt's source contains visual aids.

    And it does sound like homework.
     
  9. Jul 20, 2012 #8
    Not sure if I understand the question right, and we have seen it in regular intervals. One possible answer is that Earth gravity is strongest at the core mantle boundary.

    Earth-G-force.png


    Laurent Hodges 1991, "Gravitational field strength inside the Earth", American Journal of Physics -- October 1991 -- Volume 59, Issue 10, pp. 954-955
     
    Last edited: Jul 20, 2012
  10. Aug 11, 2012 #9

    tiny-tim

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    i'd like to add that sometimes it isn't obvious what title to look up in wikipedia … there can be more than one page on the same subject, and the best one isn't always the one with the most obvious title

    so indicating the page not only helps the OP, it also helps other readers studying the same topic :wink:

    also some wikipedia entries are very good :smile:, and it is helpful to draw attention to them!​
     
  11. Aug 23, 2012 #10
    Thank you everyone.
     
  12. Aug 23, 2012 #11

    phinds

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    It was wise of you to change the original of the above:

    since such comments will not get you far here. In fact, even posting them and then quickly changing them is not a good idea since they go out in emails to everyone subscribed to the thread.
     
  13. Aug 23, 2012 #12
    Effective gravity varies with latitude due to the centrifugal force caused by the earths spinning.
    It also depends on the density of the mantle and crust beneath a surface. Measurements of the gravity of the earth is called gravitational tomography”. Measurements have been made and analyzed.
    One approximate “rule of thumb” is that the continental rock has on average less density than deep sea floor rock. The continents are basically floating on the mantle, while the deep sea floor is mantle. However, the surface of the continent is further from the center of the earth than the sea floor. So the gravitational pull of the earth is less on the surface of a continent then above the deep sea floor. Similarly, the gravitational pull on top of a mountain is less than the gravitational pull on the surface next to it.
    This rule isn’t exact. Therefore, lots of measurements have been made to find out exactly how the density beneath the surface varies.
    Here are two links on gravimeter measurements.
    http://scintrexltd.com/downloads/GRAVGUID.pdf
    “A GUIDE TO HIGH PRECISION LAND GRAVIMETER SURVEYS
    by H.O. Seigel
    The formula for the general increase of g with latitude , based on the most
    recently accepted spheroid approximation, is given by (Moritz, 1984).
    in Gals
    (6) <see reference>
    This equation includes both the Newtonian attraction of the Earth as a
    spheroid and the centrifugal force caused by its rotation about its axis.


    http://www.gmat.unsw.edu.au/ablos/ABLOS08Folder/Session4-Paper2-Greku.pdf [Broken]
    “Abstract
    An outer edge of the continental mass is established by the foot of the continental slope in accordance with the UN Convention on the Law of the Sea (UNCLOS, article 76). It can be "visible" with the help of echo-sounding and seismic surveys. It is obvious that the real continental margin extends under upper layers of the abyssal ocean floor more seaward than the visible foot. The gravimetric tomography method [1] developed by us allows scientists to reconstruct the Earth’s internal geological structure with the satellite altimeter and geoid data to determine the real outer edge of the continental mass and the breadth of the territorial sea along the coastal countries.”
     
    Last edited by a moderator: May 6, 2017
  14. Aug 23, 2012 #13
    Yes but also from the Geoid shape, the difference with a pure spherical shape does matter, for instance on the poles versus the equator you're closer to the center of the earth, hence you have less r but also there is less mass right beneath you, as it is more to the side.

    See what Grace found for gravity:

    ggm01-200.gif

    source
     
  15. Sep 8, 2012 #14
    Gravity varies based on altitude. The higher the altitude, the farther away from the center of the Earth. So Mt. Everest has less gravity than Grand Canyon. But the difference isn't too consequential.
     
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