Variations in Earth's gravity

[BigMoosie]

I know that the variation in Earth's gravity varies due to the following (and other) reasons:

 

• Altitude
  
• Variations in the crust density
  
• Celestial objects
  
• Distance from the equator (centifugal accelleration due to Earth spinning)
  

 

But which is the most influential and what is their relative magnitudes?

[swansont]

The spinning doesn't decrease earth's gravity (neither do celestial objects) but these do reduce the net force.

 

The oblateness of the earth also causes a change in the mass distribution; if the spinning were to stop you'd see about a 0.35% increase in the net force. If the earth were to also resume a spherical shape, the total would be ~0.4%.

[Klaynos]

If you think about it, the net force (as swansont explains we're probably talking about) depends on your possition. If you're a long way above the surface then small changes in crust thickness will tend to be negligable, as will the fact the earth is not a sphere, etc... So the answer has to be cut down to be more precise, do you mean the net force on the surface?

[[Tycho?]]

There is an interesting pic floating around the net of a "gravity map" of the earth. Some sattelite flew over the earth and measured acceleration due to gravity at each point. Its quite interesting to see how it varies, especially since it seems very random (it doesn't corespond to continents, oceans, mountains or anything else from what I can remember).

 

Try looking up gravity in wikipedia.

[BigMoosie]

Sorry for using wrong terminology, and you are correct I do mean the change in the net force.

Klaynos, for a more precise question, is the gravity at the poles weaker than the gravity at the equator? Judging from the values you supplied swansont I would assume that it would be. But how about if the moon is directly over-head and if the moon was directly opposite you, what would be the relative differences? And finally how much does the Earth's orbital eccentricity effect it?

 

On a similar note I have heard that there are people who go insane on full moons (lunatics), and that they claim this is because of its gravitational pull, but that doesn't seem to make any sense seeing that the full moon depends on angles, and would be unrelated to its effect on the net force of our gravty.

 

[Tycho?] I couldn't seem to find that image.

[[Tycho?]]

http://en.wikipedia.org/wiki/Image:Southern_ocean_gravity_hg.png

 

Here is part of it, from wikipedia.

 

And I guess it was wrong, since you can obviously see that its a pic of antartica.

[Sisyphus]

Gravity is stronger at the poles, because you are closer to the center of the Earth. You also weigh less at the tops of mountains for the same reason. The added mass of the mountain directly under you (incredibly miniscule compared with the Earth) is more than cancelled out by the fact that you're farther away.

 

Note that that is at the surface, which changes in altitude. At a uniform altitude, like from a satellite, you will feel more pull when there is more stuff directly underneath.

[5614]

• Altitude
  
• Variations in the crust density
  
• Celestial objects
  
• Distance from the equator (centifugal accelleration due to Earth spinning)

But which is the most influential and what is their relative magnitudes?

As a guess I would say 1' date=' altitude.

 

On a similar note I have heard that there are people who go insane on full moons (lunatics), and that they claim this is because of its gravitational pull

Last I checked werewolves weren't real... or were you being serious?

[Guest_Jim*]

There is a satelitte that measures the gravity of the Earth. Here's it site

http://www.csr.utexas.edu/grace/