Coulomb's Law

Coulomb's law quantifies the force between two point charges. The force magnitude is directly proportional to the product of the charges and inversely proportional to the square of the distance separating them. The force acts along the line joining the charges and can be attractive or repulsive depending on charge signs.

When both charges are positive or both negative, they experience repulsive forces pushing them apart. When one charge is positive and the other negative, the force is attractive, pulling them together. In both cases, Newton's third law applies: the forces on each charge are equal in magnitude but opposite in direction.

The permittivity of vacuum, epsilon-naught, is a fundamental constant approximately 8.854 × 10⁻¹² in SI units. It appears in Coulomb's law as the proportionality constant and has significant physical meaning related to the speed of light in vacuum. This constant enables quantitative prediction of electric forces between charges.

The Coulomb force is inversely proportional to the square of the distance between charges, meaning it decreases rapidly as charges move apart. This inverse square relationship implies the force is effective only at small distances. If separation distance changes, the force magnitude changes accordingly, making direct application of Newton's laws mathematically complex.

Both forces follow inverse square laws and depend on fundamental constants. However, the comparison between electrical and gravitational forces reveals key differences: gravitational force is always attractive, while Coulomb force can be attractive or repulsive. Additionally, Coulomb force does not depend on object mass, unlike gravitational force.

No, the Coulomb force is independent of object mass. The force depends only on the magnitudes of the charges and the distance between them. This fundamental difference distinguishes electric forces from gravitational forces, which directly depend on the masses of interacting objects.

The Coulomb force is not constant; it changes as the separation distance between charges changes. If either charge moves, the distance changes and the force magnitude changes accordingly. This distance-dependent behavior makes solving problems with moving charges more complex than static situations.