Charges suspended by strings: a new twist to an old problem
  A popular problem asks for the equilibrium separation between two identical (mutually repelling) charges suspended by strings fastened to a common point. We slightly modify this problem by considering two opposite (mutually attracting) charges and adding a finite separation between the suspension points. The discussion leading to the solution introduces important physical phenomena including "catastrophic" behavior and hysterisis. 
Peretz D. Partensky and Michael B. Partensky