►The experiments about friction charge suggested that there are two kinds of electrification : (i) like charges repel and (ii) unlike charges attract each other.
►The property which differentiates the two kinds of charges is called the polarity of the charges.
►The experiments also demonstrated that the charges are transferred from the rods to the pith balls on contact. It is said that the pith balls are electrified or are charged by contact.
►When a glass rod is rubbed with silk, the rod acquires one kind of charge and the silk acquires the second kind of charge.
►Now if the electrified glass rod is brought in contact with silk, with which it was rubbed, they no longer attract each other.
►Thus, the charges acquired after rubbing are lost when the charged bodies are brought in contact.
►These observations just tell us that unlike charges acquired by the objects neutralise or nullify each other's effect.