To begin, we need to understand some basic properties of electricity. Lightning is a form of static electricity. If an object has the capability to attract and store electricity we say that this object is charged. A charge is a property of elementary particles that determines the strength of its electric force with other particles possessing charge. It is measured in coulombs. Materials that are able to transfer charge are known as conductors; those that cannot are called nonconductors, or insulators. Many charged objects have to be suspended from insulators, such as silk threads or plastic bases, or they quickly lose their charge to earth, or ground.

In fact, we speak of grounding an object to ensure that it is not charged. Other objects hold their charges without being insulated. When we charge a plastic rod by rubbing it, the charge stays on the rod even if we hold it. But our bodies are conductors. Why doesn`t the charge flow to the ground through our bodies? It stays on the rod because the rod is an insulator, charge generated at one end remains there. The charge can be removed by moving our hands along the charged end. As we touch the regions that are charged, the charges flow through our bodies to ground. A metal rod cannot be charged in this way, because metal conducts the charge to our hands. A metal rod can be charged if it is mounted on an insulating stand or if we hold it with an insulating glove; that is, the rod must be insulated from its surroundings.

Two Kinds of Charge

Before 1730, electricity was believed to be only attractive. It may seem strange to us now since both the attractive and repulsive aspects of electricity are easy to demonstrate. Comb your hair and use the comb to attract small bits of paper. After contacting the comb, some of these bits are then repelled by it.

Whenever we charge an object by rubbing it with another, both objects become charged. If two objects had the same kind of charge, they should repel one another. We are, therefore, led to the idea that there must be two different kinds of charge and that they attract each other. This can be summarized by stating: Like charges repel; unlike charges attract.

In our modern physics world view, all objects are composed of negatively charged electrons, positively charged protons, and uncharged neutrons. An object is uncharged or neutral because it has equal amounts of positive and negative charges, not because it contains no charges. Positively charged objects may have an excess of positive charges or a deficiency of negative charges. We simply call them positive objects since the electrical effects are the same in both situations.

The modern view easily accounts for the conservation of charge when charging objects. The rubbing simply results in the transfer of charges from one object to another; whatever one object loses, the other gains. Attraction is the most common electrical effect because charged objects can attract uncharged objects.