The electrostatic force between two point charges is proportional to the product of the charges, inversely proportional to the square of the distance between them, and acts along the straight line joining them.
Like charges repel with equal and opposite forces along the line joining them.
F = k × q₁q₂ / r²
F
force between the charges (newtons)
q₁, q₂
the two charges (coulombs)
r
distance between them (metres)
k
Coulomb constant ≈ 8.99 × 10⁹ N·m²/C²
In plain English: Like charges push, opposite charges pull, and the effect dies off fast with distance — halve the gap and the force quadruples. It is the electrical twin of Newton's gravity law.
Where you'll meet it: Explains static shocks, why capacitor plates attract, and how CRTs and electrostatic speakers steer charge. The starting point of all electrostatics.