We begin by considering the behavior of a pith ball placed near a charged rod. Pith balls are small conducting spheres used in the lab setting to model point-like charges, they are usually hung from strings to that the amount of the balls swing from equilibrium can be used as a qualitative measure of the strength of the force. A plastic rod is rubbed with a piece of wool or silk to give it a net charge and then an uncharged pith ball is allowed to touch the rod. This contact will charge the pith ball with the same sign charge as the rod, and thus the pitch ball will immediately recoil from the rod after they make brief contact. If the ball is placed near the rod at the points shown in the diagram below a rough estimate of the force felt by the pith ball can be recorded by measuring how much it swings away from equilibrium. an illustration of a charged rod and the forces felt by a near by pith ball The green arrows illustrate the force felt by the pith ball at each of those points. Keep in mind that these vectors carry two