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So my question is this that suppose we consider a solid everyday object, say a spherical stone. Now, if I consider an atom or a molecule of the stone away from the center of the stone, then I can say that the gravitational force on the atom/molecule is non zero due to the other atoms/molecular constituents of the stone in question. So what force balances this unbalanced gravitational force?

If it is the electric repulsion due to the other atoms then why does the body not explode outward, for the electric repulsion due to the other atoms is way stronger than the gravitational force? Or am I missing something here?

Also, does the crystal structure of arrangement of atoms inside the solid play a role in this?

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The Atoms do feel Electrostatic repulsions, so can't be compressed more than a certain extent (except the case when black holes forms). Pauli's exclusion principle, a QM-thing, is also a factor here. This is the reason atoms don't collapse under their own attractive forces, and also the reason that you are able to touch things (otherwise your atoms would pass through anything you try to touch).

But when separated apart to some distance, the Electrostatic repulsions get reduced, and the attractive forces dominate. And these attractive forces are not only gravitational, but various other types of attractions called Van der waal Forces, (or Electrostatic only, in case of salts, or Covalent bonds, if the object is a network solid like diamond).

And when an atom gets in stable equilibrium with these forces, then only it's in rest. For an everyday object, if it is in rest then there may be some net forces on some of its parts but on whole they cancel out so that the centre of mass remains at rest.

Thus, it neither explodes, nor collapse.

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  • $\begingroup$ ie you are saying that the net effect of all these forces ie electrostatic force ,gravitational force and the inter molecular force ( the van der waal force) on a certain atom within the object cancel out such that the net force on every single atom is zero $\endgroup$
    – p0803
    Commented Aug 20, 2019 at 15:37
  • $\begingroup$ But lets say , in a hypothetical condition if i was considering only the gravitational effect of all the other atoms on that single chosen atom ie ( if by some mysterious way i succed in removing all the other forces on the chosen atom due to the other atoms of the solid ) Then the net GRAVITATIONAL FORCE on the single atom would not be zero isnt it and subsequently on all the other atoms of the solid , then as the gravitational force is attractive in nature then would our stone be crushed due to its own gravitational force ? ( this is when i neglect all the other forces on it ) $\endgroup$
    – p0803
    Commented Aug 20, 2019 at 15:45
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    $\begingroup$ @p0803 you got it right. For your other question, as per my knowledge the object must collapse, and the whole universe would collapse then. But I suggest ask it separately, referencing your this question if required. $\endgroup$
    – ParadigmShift
    Commented Aug 20, 2019 at 15:56
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    $\begingroup$ But wait, the net force on every single atom may not be zero, but on average the net force is zero. ( There maybe some uncertainities, so we cannot say exactly on this.) $\endgroup$
    – ParadigmShift
    Commented Aug 20, 2019 at 16:01
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I am not sure if I fully understand your predicament here. Obviously atoms are not flying off of your object, and the object isn't imploding. So its obvious that the net forces on all parts of the object must cancel. So if you have (probably negligible) amounts of gravitational forces acting between parts of the object, and you have electric interactions acting on parts of the object, you know that these forces must cancel out as a whole. It doesn't matter how strong any single interaction could be. Forces are vector quantities, and these vectors cancel out.

Although we are getting dangerously close to getting into the realm of thinking of individual particles, QM, etc. here. I suppose if you did zoom in far enough you would find that certain parts of your object do experience net forces. But on average these will cancel out, and certainly these forces do not manifest themselves macroscopically.

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  • $\begingroup$ But what i am saying is that since the electrostatic force is way stronger than gravitational force here so how does these forces balance each other when we consider them acting on a single atom , as indivisually the net effect of these forces on a single atom is non zero .Also what is the nature of electrostatic forces that act here as the atoms here are neutral ie are they repulsive or are they attractive ? Thx $\endgroup$
    – p0803
    Commented Aug 20, 2019 at 16:25
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    $\begingroup$ @p0803 Forces are vectors. You cannot just compare vector magnitudes to know whether they cancel out or not. Also, vectors don't cancel based on type of force. They are all forces. It is not the case that you need to match the electric force to the gravitational force. Ultimately you should be able to neglect gravity entirely. The electric forces should all cancel each other out $\endgroup$
    – BioPhysicist
    Commented Aug 20, 2019 at 16:29

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