When we walk across the carpet in dry weather and then touch the metal door knob a spark can be drawn. This is due to transfer of electric charge.

And lightening is also a phenomenon that occurs due to transfer of charge.

Such phenomena suggest that there is a large amount of charge stored in the objects surrounding us. The electric neutrality of objects suggest that there is an equal amount of positive and negative charge in different objects around us. We call a body to be charged if its positive and negative charges are not equal.

Charged bodies exert force on each other. We show this by an experiment, let us consider a glass rod. We rub it with with silk. Rubbing slightly disturbs the electric neutrality of both the objects. Now we suspend the charge with a light string, now if we bring another charged rod of the same charge as that on the suspended rod then it will repel the suspended rod and if it has a charge of the opposite charge as that on the suspended rod then it will attract the suspended rod.

Thus we can now conclude that:

Same charges repel each other and opposite charges attract each other.

 

This attractive or repulsive force is called electrostatic force of attraction or repulsion. We consider those charges which are at rest or moving very slowly with respect to each other. The branch of physics in which we study such charges is called Electrostatics. Benjamin Franklin gave the positive and negative labels to the charges. The electrical forces between charged bodies have many industrial applications. Among which electrostatic paint spraying and powder coating, fly-ash precipitation, nonimpact ink-jet printing and photocopying are common.