Two equally charged pith balls of equal mass are separated by a distance , due to their mutual electrostatic repulsion. Each ball hangs on a string of length from a common point, making an angle with the horizontal. The value of the angle , the charge , and the tension of the string are calculated.

By trigonometry, the angle is equal to , the value of the charge is , and the tension is , where is the acceleration of gravity and is the constant in Coulomb's law.