# Coulomb's law

Charles Augustin de Coulomb

Coulomb's law is a function developed in the 1780s by physicist Charles Augustin de Coulomb. It explains how strong the force will be between two electrostatic charges. Electrostatic means electric charges without any motion.

## Direction

This picture shows how Coulomb's Force act; similar charges pushing against each other and opposite charges attract each other

Let's think of two electric charges existing in an empty space. If the two charges are opposite, (+) and (-) charges for example, they will attract each other. And if two charges are both the same, both (+) or both (-) for example, they will push each other. This is similar to how magnets act, as N and S attract each other, and as N and N, S and S push each other.

This is because electric charges make an electric field. If two fields exist in the same space at the same time, then the two fields exert (~ put) force on each other. The force they make on each other is called Coulomb's force or electrostatic force. Coulomb's law explains how big the force will be.

## Scale

Coulomb's law explains the scale between two electric charges. The scale of electrostatic force follows the function below.

${\displaystyle F={K_{c}}{\frac {q_{1}q_{2}}{r^{2}}}}$

Coulomb's law explains that the force scale F is relative to ratio of ${\displaystyle q_{1},q_{2}}$,${\displaystyle {\frac {1}{r^{2}}}}$.

${\displaystyle q_{1}}$ and ${\displaystyle q_{2}}$ are the scales of each electric charge. ${\displaystyle r}$ is the distance between the two electric charges. And ${\displaystyle K_{c}}$ has a certain value. It does not change relative to ${\displaystyle q_{1}}$, ${\displaystyle q_{2}}$ or ${\displaystyle r}$. While ${\displaystyle {K_{c}}}$ remains constant, when multiples of ${\displaystyle q_{1}}$ and ${\displaystyle q_{2}}$ become bigger, the electrostatic force will also get bigger. When the distance ${\displaystyle r}$ become bigger, the electrostatic force will become smaller to ratio of ${\displaystyle {\frac {1}{r^{2}}}}$.
The exact size of ${\displaystyle K_{c}}$ is {\displaystyle {\begin{aligned}k_{c}&=8.987\ 551\ 787\ \times 10^{9}\\\end{aligned}}} ${\displaystyle \approx 9\times 10^{9}}$N m2 C−2 (or m F−1). This constant is called Coulomb's Force Constant or Electrostatic Force Constant.

## Inverse-square law

The relation between the force of pushing or pulling (F) and the distance between the particles (${\displaystyle r}$) follows the Inverse-square Law. Inverse-square law means that when the distance ${\displaystyle r}$ grows bigger, the force gets weaker by the ratio ${\displaystyle {\frac {1}{r^{2}}}}$. Gravitation, Electromagnetic radiation, and sound loudness also follows this law.