brought near the first rubber rod; the rods repel each other. Now if we bring a charged glass rod close to the charged rubber rod, they attract each other. At the same time, if a charged glass rod is brought near another charged glass rod, both the rods repel each other. From these observations, the following inferences are made (i) The charging of rubber rod and that of glass rod are different from one another.
(ii) The charged rubber rod repels another charged rubber rod, which implies that ‘like charges repel each other’. We can also arrive at the same inference by observing that a charged glass rod repels another charged glass rod. (iii) The charged rubber rod attracts the charged glass rod, implying that the charge in the glass rod is not the same kind of charge present in the rubber. Thus unlike charges attract each other.
Therefore, two kinds of charges exist in the universe. In the th century, Benjamin Franklin called one type of charge as positive (+) and another type of charge as negative (–). Based on Franklin’s convention, rubber and amber rods are negatively charged while the glass rod is positively charged. If the net charge is zero in the object, it is said to be electrically neutral.
(i) When an object is pushed, the atoms in our hand interact with the atoms in the object and this interaction is basically electromagnetic in nature. (ii) When we stand on Earth's surface, the gravitational force on us acts downwards and the normal force acts upward to counter balance the gravitational force. What is the origin of this normal force? It arises due to the electromagnetic interaction of atoms on the surface of the Earth with the atoms present in the feet of the person.
Though, we are attracted by the gravitational force of the Earth, we stand on Earth only because of electromagnetic force of atoms. (iii) When an object is moved on a surface, static friction resists the motion of the object. This static friction arises due to electromagnetic interaction between the atoms present