Rub a balloon on your hair and it sticks to the wall — that invisible grip is Coulomb's law at work, and it is astonishingly strong. Coulomb's law says the electrostatic force between two point charges is F = k·q₁·q₂/r², where k ≈ 8.988 × 10⁹ N·m²/C². The force grows with the product of the charges and dies off with the square of the distance — double the separation and the force drops to a quarter. The sign tells the story: like charges repel (positive force), opposites attract.

It is the same inverse-square shape as Newton's gravity, but enormously stronger — the electric repulsion between two protons outweighs their gravitational attraction by a factor of about 10³⁶. AP Physics students use it for point-charge problems, and it underlies everything from photocopier toner to the repulsion that keeps atoms from collapsing. Enter both charges in coulombs and their separation in meters to get the force in newtons.

With the pre-filled defaults — Charge 1 (q1, C) 0.000001, Charge 2 (q2, C) 0.000002, Distance (r, m) 0.1 — the Coulomb Law Calculator returns Electrostatic Force (F, N) 1.7975. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.