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Each object in the universe has its own gravitational influence on all other objects in the universe. What distance do they have to be from each other to create only one gravitational influence? Example - Every human does in my opinion contribute to the earth gravitation thanks to the mass of our bodies. Now would there be a difference if I distanced myself from the surface by any amount?

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  • $\begingroup$ In other words, at what point does an object stop contributing to the gravity of a larger object? $\endgroup$ – Scottie Nov 12 '14 at 15:10
  • $\begingroup$ Yes. I would really like to know this. $\endgroup$ – Boris Bucek Nov 12 '14 at 15:33
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What id like to know, in what distance do they have to be from each other to create only one gravitational influence.

At whichever point you decide to call them two objects rather than one object. It's a completely arbitrary choice that depends on you rather than gravitational physics. What's going on is that gravity can be described by a mass density distribution, and which part of that distribution corresponds to "one object" and which to "another object" isn't important.

You may be confused by Newton's law of gravity that says the gravitational force force is proportional to the product of the masses and inversely proportional to the distance between them squared. But this law only applies to spherically symmetric objects. It only applies to you exactly if you're a spherical cow.

This kind of arbitrariness actually applies to the Earth as well. Even if the Earth were perfectly spherically symmetric, one could say that Earth's gravity is due to the influence of the northern hemisphere and the influence of the southern hemisphere, etc. Whether you consider the Earth to be one object, or two, or a trillion, depends on you.

The Earth isn't spherically symmetric. It's closer to an oblate spheroid, since it bulges at the equator. But it isn't exactly that either, having mountains or other topographical feature, to say nothing of mass density variations inside the Earth. In principle, one could describe its gravity including people and trees or whatnot. Gravitationally, there is no fundamental difference between you and some rock. That you consider yourself to not be "part of Earth" is a choice you make for other reasons.

If you distance yourself from the Earth, there is a difference because the mass distribution would change. But again, whether you consider this to be "only one gravitational influence" or "the Earth plus you" is up to you, and this holds true regardless of whether you distanced yourself or not.

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  • $\begingroup$ So simply put i could say that earths gravity is something like sum of all the objects that its made of and the border from which 2 objects dont act as if they were one depends only on my opinion. Thank you very much for answer. Im going to mark this one as good but feel free to add something if i understood it wrong. $\endgroup$ – Boris Bucek Nov 12 '14 at 17:45
  • $\begingroup$ @BorisBucek That's right; e.g., one could also say that the Earth's gravity is the influence of all of its constituent atoms, etc. Although quite often, breaking up a system into parts in one way rather than another way makes things easier or even established by the kind of question being asked--if you're interested where to point your telescope for Mercury, then you're treating 'Mercury' as one object; on the other hand, there's nothing preventing you from thinking 'solar system' as one object either. How you break it up depends on what you're interested in and what you find convenient. $\endgroup$ – Stan Liou Nov 12 '14 at 18:07
  • $\begingroup$ +1 for the spherical cow reference. . . Seriously, though, that's a good way to explain how many basic laws are only totally accurate for idealized scenarios. $\endgroup$ – HDE 226868 Nov 12 '14 at 21:28

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