Most of the forces in physics obey inverse square law, but why molecular forces don't obey it.. Since molecular forces is also a form of electromagnetic force..
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1$\begingroup$ do read up on van der Waals forces en.wikipedia.org/wiki/Van_der_Waals_force $\endgroup$– anna vMar 17, 2013 at 14:01
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3 Answers
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Molecular forces obbey that law (since it's all electromagnetism), the difference is that in those cases you don't have just two charges, but a more complex set of charges that interact, and maybe those inverse square laws, when superpositioned, don't form another inverse square.
The most simple example of this is an electric dipole: two charges separated by a distance $d$, generally small. When you go far away, it turns out that the electric potential goes as an inverse square, and the force goes as $1/r^3$, instead of $1/r^2$.
answered Mar 17, 2013 at 13:04
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The main reason is the neutrality of molecules, so if you consider it like a point, you will not have an interaction at all. For systems with non-zero summary charge the small dipole, quadrupole, ..., $2^n$-pole fields will be negligible additions compared to Coulomb law on the large distances, but for totally uncharged system summary force or field begins from dipole, since $Q=0$.
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It is argued that the inverse square law does not apply in charged molecule interaction on the basic that other forces might counter it in some way, especially if they are in close proximity.
But that is not an argument against the law applying in these cases, only what the resultant position might be.
It is inconceivable that the inverse square law does not work at the molecular level.
For example, enzyme reactions can occur at such speeds that substrates would need to accelerate to the active site and the product accelerate away from them, after being made (which the inverse inverse square law would enable in both cases to take place), to account for them.
