Static Electricity

All matter contains electric charge: positive charge and negative charge. Normally an object has equal amounts of each, so it is neutral — the charges cancel out and you notice nothing.

When two different materials are rubbed together, tiny negatively charged particles (electrons) are transferred from one to the other:

• The material that gains electrons becomes negatively charged.
• The material that loses electrons is left positively charged.

Charge that stays where it is put — usually on an insulator such as plastic or wool — is called static electricity. "Static" means stationary.

The rules of charge:

In short: like charges repel, unlike charges attract.

Worked example. A plastic ruler is rubbed on a woollen jersey and then held just above small torn pieces of paper. The paper jumps up and sticks to the ruler. But the paper was never rubbed — so how can it be attracted?

1. Rubbing transfers electrons from the wool onto the ruler, so the ruler is negatively charged.
2. The paper is neutral overall, but its charges can shift slightly. The ruler's negative charge pushes the paper's negative charges to the far side of each piece.
3. That leaves the near side of the paper slightly positive.
4. Positive near side + negative ruler = attraction, and the paper is light enough to lift.

This is why a charged object attracts neutral objects too — a detail most people miss.