HOME	Static electricity - background information for the teacher

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The topic static electricity has at least two similarities to the topic magnetism: the seemingly magical attraction and repulsion of one object for another, and the attraction of people of all ages to the topic. Another common thread between the two subjects is that our understanding of both of them is still based largely on theory. Through observation and experimentation, logical explanations of the phenomena have developed.

An understanding of static electricity must begin with the concept that all matter is composed of atoms, and all atoms are composed of subatomic particles among which are the charged particles known as electrons and protons. Protons carry a positive charge (+), and electrons carry a negative charge (-). Ordinarily every object carries equal numbers of protons and electrons and is said to have a neutral charge.

When two different materials come into close contact -- for example, felt rubbing against a balloon, or two air masses in a storm cloud -- electrons may be transferred from one material to the other. When this happens, one material ends up with an excess of electrons and becomes negatively charged, while the other ends up with a deficiency of electrons and becomes positively charged. This accumulation of imbalanced charges on objects results in the phenomena we commonly refer to as static electricity.

Materials that bear imbalances of opposite charge will attract each other and cling together. Materials that bear imbalances of like charge will repel each other. When an object bearing an enormous accumulation of positive or negative charge comes close to another object bearing the opposite charge, a spark may jump across the space between them. This results in both the enormously powerful discharges of lightning and the small yet stimulating shocks we receive when touching something after shuffling across a carpet in our stocking feet.

Because wool cloth is a material that readily gives up electrons, it is used in many activities to produce an accumulation of negative charge on an otherwise neutral object. Human hair is another common material that readily gives up electrons.

A material such as rubber is known as an electrical insulator. Accumulations of charge will not move across the surface of a rubber object easily. When one part of a balloon is rubbed with wool, the wool gives up electrons, making that part of the balloon negatively charged even though the rest of the balloon may remain neutrally charged.

When a charged object such as a balloon that has been rubbed with wool is brought near a neutrally charged object such as a piece of Styrofoam, the Styrofoam is said to become positively charged by induction and may leap toward the charged balloon. An object charged by induction does not actually have to lose or gain electrons. A negatively charged balloon brought near a neutrally charged piece of Styrofoam repels the electrons on the surface of the Styrofoam. The repelled electrons migrate as far away from the balloon as possible. This leaves the near end of the Styrofoam with an imbalance of positive charge and results in the attraction of the Styrofoam for the balloon.

It is important that elementary students grasp the concept that oppositely charged objects will attract each other and like charged objects will repel each other. It is less important that they are able to recall which materials tend to acquire negative or positive charges.

Do make sure that your students have a chance to make connections between their day-to-day experiences with static electricity -- lightning, receiving shocks after shuffling across a carpet, clothes that cling coming out of the dryer, combing their hair in the wintertime, etc.-- with the static activities conducted in the classroom. Ask them to try to describe and explain their everyday experiences with static in the terms they are learning: repel, attract, static charge, electron transfer.

One final note: static electricity activities can be conducted successfully at any time of the year. However, they will be most successful and exciting on days when there is low relative humidity. When there is a large amount of moisture in the air, some of it forms a coating on the surfaces of objects. This surface coating of moisture can neutralize a build-up of static charge. This is why we can shock ourselves in the dry air of winter more easily than we can during the humidity of summer.