PURPOSE: To demonstrate "charging by friction."

DESCRIPTION: Rubbing silk on a glass rod makes the glass positive and the silk negative. Rubbing fur on a hard rubber rod makes the hard rubber negative and the fur positive. This effect is known as "triboelectricity," from the Greek "tribein," or to rub. The positively charged glass rod and the negatively charged hard rubber rod can then be used (1) simply to illustrate that electrical charge exists using an electroscope or (2) to perform other electrostatics experiments.

SUGGESTIONS:

EQUIPMENT: Glass rod with silk, hard rubber rod with fur, projection electroscope, overhead projector for projection.

SETUP TIME: 15 min.