# Coulomb

## Coulomb (Encyclopedia of Science)

A coulomb (abbreviation: C) is the standard unit of charge in the metric system. It was named after French physicist Charles A. Coulomb (1736806), who formulated the law of electrical force that now carries his name. (A physicist is one who studies the science of matter and energy.)

Coulomb's law concerns the force that exists between two charged particles. Suppose that two ping-pong balls are suspended in the air by threads at a distance of two inches from each other. Then suppose that both balls are given a positive electrical charge. Since both balls carry the same electrical charge, they will tend to repelr push away fromach other. How large is this force of repulsion?

History

The period between 1760 and 1780 was one in which physicists were trying to answer that very question. They already had an important clue as to the answer. A century earlier, English physicist Isaac Newton (1642727) had discovered the law of gravity. Two objects attract each other, that law says, with a force that depends on the masses of the two bodies and the distance between them. The law is an inverse square law. That is, as the distance between two objects doubles (increases by 2), the force between them decreases by one-fourth (1 ÷ 22). As the distance between the objects triples (increases by 3), the force decreases by one-ninth (1 ÷...

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