In U.S. politics, an organization whose purpose is to raise and distribute campaign funds to candidates seeking political office. PACs rose to prominence after the Federal Election Campaign Act (1971) limited the amount of money any corporation, union, or private individual could give to a candidate. PACs were able to circumvent these limits by soliciting smaller contributions from a much larger number of individuals. During the late 20th and early 21st centuries the vast amounts of money raised by PACs greatly increased the cost of running for office and led to efforts to reform this method of financing campaigns.
Learn more about political action committee (PAC) with a free trial on Britannica.com.
Fundamental law of chemical kinetics (the study of rates of chemical reactions), formulated in 1864–79 by the Norwegian scientists Cato M. Guldberg (1836–1902) and Peter Waage (1833–1900). The law states that the reaction rate of any simple chemical reaction is proportional to the product of the molar concentrations of the reacting substances, each raised to the power corresponding to the number of molecules of that substance in the reaction.
Learn more about mass action, law of with a free trial on Britannica.com.
Type of breech mechanism that was key to developing an effective repeating rifle. It combines the firing pin, a spring, and an extractor, all housed in or attached to the bolt. A projecting handle with a round knob moves the bolt back and forth. As the bolt is thrust forward, it pushes a cartridge into the chamber and cocks the piece. The trigger releases the spring-driven firing pin inside the bolt. After firing, the extractor on the head of the bolt removes the spent cartridge and ejects it. The bolt then moves a new cartridge from the magazine.
Learn more about bolt action with a free trial on Britannica.com.
In the U.S., the effort to improve the employment and educational opportunities of women and members of minority groups through preferential treatment in job hiring, college admissions, the awarding of government contracts, and the allocation of other social benefits. First undertaken at the federal level following passage of the landmark Civil Rights Act of 1964, affirmative action was designed to counteract the lingering effects of generations of past discrimination. The main criteria for inclusion in affirmative action programs are race, sex, ethnic origin, religion, disability, and age. The Supreme Court of the United States placed important limitations on affirmative action programs in its 1978 ruling in
Learn more about affirmative action with a free trial on Britannica.com.
Sports events characterized by high speed or high risk. Such sports include aggressive inline skating, wakeboarding, street luge, skateboarding, and freestyle bicycle events (wherein tricks such as back flips are performed on a bicycle). Many of the events—snowboarding, skateboarding, and freestyle biking are examples—are performed on ramps and inclines or in a halfpipe, some with walls as high as 50 feet, which allows the athletes to get air, or achieve the height necessary to, for example, rotate on a bicycle. Many of these sports were made popular by the X Games (championship competitions sponsored by the cable-television network ESPN). The 1998 and 2002 Olympic Games featured extreme snowboarding events in a halfpipe, in which boarders performed jumps, rotations, and mid-air maneuvers.
Learn more about extreme sports with a free trial on Britannica.com.
Brief (about one-thousandth of a second) reversal of electric polarization of the membrane of a nerve or muscle cell. Stimulation of the cell by certain chemicals or by sensory receptor cells causes depolarization of the membrane, permitting an impulse to move along the nerve fibre (in nerve cells) or causing the cell to contract (in muscle cells).
Learn more about action potential with a free trial on Britannica.com.
Action may refer to: