# Gravity equal on all parts of earth? **URL:** \ **Category:** Factual Questions\ **Created:** [July 22, 2003, 12:38am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048 "2003-07-22T00:38:19Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Brad\_Amundsen](https://avatars.discourse-cdn.com/v4/letter/b/dbc845/32.png) [@Brad\_Amundsen](https://boards.straightdope.com/u/Brad_Amundsen)\ **Post date:** [July 22, 2003, 12:38am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/1 "2003-07-22T00:38:19Z")
Is the gravitational pull exactly equal on all parts of the earth? In other words will I weigh exacty the same no matter where I am at on the surface of the earth? Is there any variance at all anywhere? Mountain Top? Lowest valley? Over Water? Etc… ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 22, 2003, 12:40am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/2 "2003-07-22T00:40:56Z")
Nope. There’s variations due to many, many factors, including altitude, latitude, composition of the Earth under you, and tidal forces to name the major ones. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 22, 2003, 12:52am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/3 "2003-07-22T00:52:23Z")
> [@](#): > > Is the gravitational pull exactly equal on all parts of the earth No, and here is a map to prove it: [http://antwrp.gsfc.nasa.gov/apod/ap011113.html](http://antwrp.gsfc.nasa.gov/apod/ap011113.html) ---
**Author:** ![K364](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k364/32/5_2.png) [@K364](https://boards.straightdope.com/u/K364)\ **Post date:** [July 22, 2003, 12:53am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/4 "2003-07-22T00:53:10Z")
I believe that gravity would be weakest on Mauna Loa, Hawaii - it is sitting near the equator, and the equatorial bulge combined with it’s height make it the farthest surface point from the centre of the earth. ---
**Author:** ![K364](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k364/32/5_2.png) [@K364](https://boards.straightdope.com/u/K364)\ **Post date:** [July 22, 2003, 12:54am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/5 "2003-07-22T00:54:40Z")
… I lied, Mauna Kea is 35 meters taller! ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 22, 2003, 1:04am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/6 "2003-07-22T01:04:20Z")
"present surface features do not appear dominant. Scientists hypothesize that factors that are more important lay in deep underground structures and may be related to the Earth’s appearance in the distant past. " [http://antwrp.gsfc.nasa.gov/apod/ap011113.html](http://antwrp.gsfc.nasa.gov/apod/ap011113.html) "if you want to lose weight you should go to India, where the pull of gravity is slightly less than it is elsewhere on the planet. You would be slightly less than 1% lighter there. " [http://news.bbc.co.uk/1/hi/sci/tech/1668872.stm](http://news.bbc.co.uk/1/hi/sci/tech/1668872.stm) ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [July 22, 2003, 1:15am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/7 "2003-07-22T01:15:04Z")
**K362** Also, the rotation of the Earth would contribute to a Hawaiian location having weaker gravity. Incidentally, I once read (of course this might be “old news”) that gravity is weakest in East Africa and strongest in Northern Norway. Your gravity may vary. ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [July 22, 2003, 1:16am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/8 "2003-07-22T01:16:25Z")
Actually, as Mauna Loa is igneous, and thus dense, gravity is a little greater there. ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [July 22, 2003, 1:46am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/9 "2003-07-22T01:46:29Z")
[Hawaiin volcanoes](http://volcano.und.nodak.edu/vwdocs/hawaii_review/intro/intro.html) Gravity measurements are one of the oldest geophysical methods of exploring the subsurface of the earth. The object is to identify variations at the surface that allow you to map changes in the density of the rock column. As an example of how it might be used, on a reflection seismic section an igneous body and a salt body may be indistinguishable. That’s because they are both relatively homogenous (thus no internal structure is revealed by seismic because there are no significant acoustic contrasts) high velocity bodies. They generally show up as a noisy area with a strong reflection at their edges. A gravity survey would distinguish between the two as the igneous rock will be significantly denser than the surrounding sedimentary rocks, yielding a gravity maximum at the surface, while the salt will be less dense and yield a minimum. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [July 22, 2003, 11:23am UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/10 "2003-07-22T11:23:54Z")
> [@](#): > > I believe that gravity would be weakest on Mauna Loa, Hawaii - it is sitting near the equator, and the equatorial bulge combined with it’s height make it the farthest surface point from the centre of the earth. Actually, the point of the Earth’s surface furthest from the centre of the Earth is the summit of [Mount Chimborazo](http://www.jagged-globe.co.uk/exp/itinerary/ecuador+volcanoes.html) in Ecuador. Not sure how the gravity stacks up there, though. ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [July 22, 2003, 1:40pm UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/11 "2003-07-22T13:40:47Z")
Remember gravity gets weeker as you go down as well as as you go up. The Marianas trench is deeper than all mountains are high (though I haven’t corrected for the bulge…) But IIRC on a sphere gravity decreases twice as fast as you go up than down, though, so Marianas’s wouldn’t get a look in in the ‘least gravity’ stakes after all, not being twice as deep. Anyone want to check my calculations? ---
**Author:** ![Shalmanese](https://avatars.discourse-cdn.com/v4/letter/s/45deac/32.png) [@Shalmanese](https://boards.straightdope.com/u/Shalmanese)\ **Post date:** [July 22, 2003, 4:24pm UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/12 "2003-07-22T16:24:29Z")
On a sphere of uniform density, gravity decreases as the inverse square of distance as you go up and linearly with distance as you go down. ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [July 22, 2003, 4:56pm UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/13 "2003-07-22T16:56:15Z")
> [@](#): > > \*Originally posted by Shalmanese \* > \*\*On a sphere of uniform density, gravity decreases as the inverse square of distance as you go up and linearly with distance as you go down. \*\* Yes, that’s what I got, but is that inversely with the square of the distance _from the centre_? Assuming the height above the surface is by comparison small, I thought it better to expand 1/(r+x)^2 to iirc (1/r^2)(1-2x+O(x^3)). ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 22, 2003, 4:57pm UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/14 "2003-07-22T16:57:36Z")
> [@](#): > > \*Originally posted by Shalmanese \* > \*\*On a sphere of uniform density, gravity decreases as the inverse square of distance as you go up and linearly with distance as you go down. \*\* Only if you considerd the center of the sphere to be your reference point. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 22, 2003, 8:23pm UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/15 "2003-07-22T20:23:28Z")
Variations in the gravitional force on satellite’s results in minor perturbations of their orbits. This has allowed scientists to determine that the sourthern hemisphere is slightly “bulgier” than the northern and the south pole is a few hundred feet closer to the center of mass than is the northern. The mass of the earth is thus not uniformly distributed and there are slight variations in gravity because of that in addition to variations from altitude etc. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [July 23, 2003, 2:06pm UTC](https://boards.straightdope.com/t/gravity-equal-on-all-parts-of-earth/190048/16 "2003-07-23T14:06:17Z")
[Nasa maps the Earth’s gravity](http://antwrp.gsfc.nasa.gov/apod/astropix.html)