Electrostatic Force - Coulomb's Law

In 1785, Coulomb published observations on how electric charges behave,

1. Opposite charges attract each other
2. Like charges repel each other
3. The force by which the charges attract or repel each other is called electrostatic force
4. As the charges are separated - the force decrease by square of the distance of separation

Info

For $F$ as electrostatic force between two charges $q_1$ and $q_2$ separated by a distance $r$,

$F=k\ast (q_1\ast q_2/r^2)$

where coulomb’s constant, $k=8.99\ast 10^{9}N{m}^2/C^2$

Why do opposite charges attract and like charges repel?

1. Positive charges have an electric field lines that radially exit the charge
2. Negative charges have an electric field lines that merge towards the charge
3. The most definite reason of attraction or repulsion cannot be concluded, but can be explained through,
   1. Field Lines: When positive and negative charges are close by, the positive charge emits while the negative charge absorbs the field lines, as a result attract each other to decrease the potential energy of the system/achieve energy conservation
   2. Quantum Electrodynamics (QED): There is a photon exchange that happens between two charges, based on this interactions the directional nature of electrostatic force is determined. Another aspect to this is based on how the charges interact with the photon field that is spread across - the charges might be coupling differently leading to a outward or inward field lines - the system in interaction with multiple charges attempts to settle on the most energy stable position leading them to loose energy in the form of motion.