1. The problem statement, all variables and given/known data Bead (mass point - mass m and charge q) is free to move in a horizontal tube (without friction). The tube is between two spheres (separated by a distance 2a) with charges Q = − q. What is the frequency of small oscillations around the equilibrium point of the bead? 2. Relevant equations Coulomb's law 3. The attempt at a solution Hmm... Coulomb's law defines electrostatic interaction between two spheres. The spheres have same charges - repel, but the bead have opposite charge, so the spheres and repel attract. It causes oscillation? Then we may use an equation for the mechanical oscillation... I don't know how combine mechanical oscillation and electrostatic interaction in one equation. Can you help me? Thank you very much and sorry for my bad English.