De wet van Coulomb

Electrical experiments lead to a mathematical law that quantifies observations. Coulomb's law formulates the force of attraction or repulsion between two point charges.

Consider two electrically charged point masses, with charges q-1 and q-2. They experience the same magnitude of force, called the Coulomb force. It is directly proportional to the product q-1-q-2 and inversely proportional to the square of the distance between them. It acts along the imaginary line joining them.

In the SI units, the proportionality constant is approximately 8.988 times 10⁹. For theoretical reasons, it is described via another constant, epsilon-naught, known as the permittivity of vacuum. Its value is 8.854 times 10^-12 in SI.

If both the charges are positive, or both are negative, they experience equal and opposite force away from each other. If one charge is positive and the other is negative, the force is attractive and equal.

The inverse square nature of the force implies that it is effective only at small distances. Friction is an example of a Coulomb force.