Chapter 4: Q5DQ (page 712)
An uncharged metal sphere hangs from a nylon thread. When a positively charged glass rod is brought close to the metal sphere, the sphere is drawn toward the rod. But if the sphere touches the rod, it suddenly flies away from the rod. Explain why the sphere is first attracted and then repelled.
Short Answer
The objects attract initially because negative charge is induced on the metal sphere. But when they touch, charges flow in both direction with a surplus of positive charge build up finally that causes repulsion.