Coulomb's law calculator

The force with which one point charge acts on another is proportional to the product of the magnitudes |q₁|·|q₂| and inversely proportional to the square of the distance r between them. The signs do not enter the formula — they only set the direction: like signs repel, unlike signs attract (on the scene the arrows F₁ and F₂ either point away from each other or toward each other). The forces on the two charges are equal in magnitude and opposite in direction — Newton's third law. The inverse square is the key part of the formula: half the distance — four times the force, a third of the distance — nine times. Example: q₁ = q₂ = 5 nC = 5·10⁻⁹ C, r = 0.4 m → F = 9·10⁹ · (5·10⁻⁹)² / 0.4² ≈ 1.4·10⁻⁶ N. The law holds for point charges (or balls much smaller than r) in vacuum.