Intersection of a polyhedron with a line

In physics, Coulomb's law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions exerts on another. It is named after Charles-Augustin de Coulomb who used a torsion balance to establish it.

The magnitude of the electrostatic force between two point charges is directly proportional to the magnitudes of each charge and inversely proportional to the square of the distance between the charges.

For calculating the direction and magnitude of the force simultaneously, one will wish to consult the full vector version of the Law

${\vec {F}}={\frac {1}{4\pi \epsilon _{0}}}{\frac {q_{1}q_{2}}{|{\vec {r}}|^{3}}}{\vec {r}}={\frac {1}{4\pi \epsilon _{0}}}{\frac {q_{1}q_{2}}{|{\vec {r}}|^{2}}}{\hat {r}}$

where ${\vec {F}}$ is the electrostatic force vector, $q_{1}$ is the charge on which the force acts, $q_{2}$ is the acting charge, ${\vec {r}}={\vec {r_{1}}}-{\vec {r_{2}}}$ is the distance vector between the two charges, ${\vec {r_{1}}}\$ is position vector of $q_{1}$, ${\vec {r_{2}}}\$ is position vector of $q_{2}$, ${\hat {r}}$ is a unit vector pointing in the direction of ${\vec {r}}$, and $\epsilon _{0}$ is a constant called the permittivity of free space.

This vector equation indicates that opposite charges attract, and like charges repel. When $q_{1}q_{2}\$ is negative, the force is attractive. When positive, the force is repulsive.