Scalar Form of Coulomb's Law

Statement: The force of attraction or repulsion between two point charges at rest is directly proportional to the product of the magnitudes of the two charges, and inversely proportional to the square of the distance between them; this force always acts along the straight line joining the two charges.

For two point charges $q_1$ and $q_2$, at rest with respect to each other and separated by a distance r, the magnitude F of the force between them is given by $F\propto\frac{q_1q_2}{r^2}\quad\Rightarrow\quad F=K\frac{q_1q_2}{r^2},$ where K is a constant of proportionality whose numerical value depends on the system of units used for F, $q_1$, $q_2$ and r, and also on the properties of the surrounding medium (vacuum, air, water, etc.). The force is ATTRACTIVE if the two charges are unlike (one positive, one …