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# Gravity and distance?

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Hi, i have a question but due my n00bness it might look a little stupid or something, anyway here it is: I was wondering how the strength of gravity (maybe not gravity, i mean the force planets and stars excersize at eachother, please tell me if that''s not gravity ) decreases when distance increaces, is it linearly or exponentially or something else (i expect that). Can anyone give me the basic formula or equation? Thanks in advance! Ow, and if i said something stupid please tell me so i can learn . And also i was wondering if anyone knows an article (or a serie of articles) about the atom structure (i know the molecule basics already from secondary school, maybe not enough but i will figure things out as i read), just interested. I don''t mind a difficult to understand article, i will figure it out (i got the time, the discipline and the will ).

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One of newtons laws :

F =G mM/R^2

G gravitational constance, m & M mass of bodies, and R is the distance seperating them.

G is something like 6.6x10^8, cant quite remember....

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Thanks! Is R measured from the centre of the objects? i guess so but just to be sure.

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Yes, gravity is calculated from the center of gravity (doesn''t it sound obvious that way?)

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G = 6.67 * 10^-11

you don''t wanna live in a universe where G is "6.6x10^8"

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good call Lord Gzoo. Did say I couldn''t quite remember though ;-)

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*Auch* (for a very short time)

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I would just like to note that the force of gravity is proportional to 1/R^2 only outside of the mass of the object. Inside it's proportional to R (assuming a pretty even density distribution). So the graph of the force of gravity looks something like this:

gravity|      /|     /  \_|    /     \          |   /       \__|  /           \____| /                 \____________|/_______________________________\________________-radius0       |     radius object(you're going to have to assume that the second part of that graph is smooth and roughly resembles 1/R^2 :)

EDIT ok the graph doesn't want to turn out right but you get the idea.

[edited by - uber_n00b on June 3, 2004 2:34:35 PM]

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I''ve never heard that before, why is that so?

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Imagine you would dig a hole right through the earth. Now If you were to drop through that hole, gravity would get less and less, until at the center of the earth, you have no gravity. why? because if you were to calculate gravity separately for every single atom in the earth once you start falling ''into'' the earth some of them would actually be pulling away from the center of gravity, effectively decreasing the force of gravity.

The center of gravity of an object is basically just a summed value of all its parts. Once you are inside this object, things get more complicated though.

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