Static Electricity, a motionless electrical charge, as distinguished from current electricity. The theoretical aspects of static electricity are discussed in the article Electricity, subtitles The Nature of Electricity: Static and Current Electricity; and How Electricity Is Produced: Static Electricity. This article is concerned with some of its occurrences, hazards, and uses.
When the relative humidity is low, as in a region with a dry climate or in a heated building during winter, static electricity is sometimes encountered. Under such dry conditions, a person walking across a carpeted floor can build up a static charge because of the friction of his shoes on the carpet. When the person touches an object that is uncharged or that has an opposite charge, the static charge is released quickly. Although annoying, such static shocks are usually harmless. Another common, but dangerous, example of the discharge of static electricity is lightning. Lightning occurs when a storm cloud builds up very large static charges.
In manufacturing industries, static electricity can be both a serious nuisance and a major safety hazard. In a paper mill, for example, static electricity may cause sheets of paper to cling together, creating delays and extra expense for the manufacturer. Large static charges may develop on drive belts between motors and machinery; if not diverted through proper grounding, the built-up static charges may discharge suddenly and cause damage to equipment. In areas containing explosive materials, great care must be taken to prevent static discharges, since a spark could set off a violent blast.
Under the proper conditions, static electricity can be very useful. Electrostatic precipitators are used to trap dust and other air pollutants in some factories and home heating and air conditioning systems. A widely used business machine, the electrostatic copier, provides quick and accurate copies of documents and drawings. Very large static charges, for use in nuclear research and in special X-ray work, can be produced by special machines such as the Van de Graaff generator.