# Why molecular forces do not obey inverse square law?

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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do read up on van der Waals forces en.wikipedia.org/wiki/Van_der_Waals_force –  anna v Mar 17 '13 at 14:01

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 $1/r^2$.

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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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