The cycle per second is a once-common English name for the unit of frequency now known as the hertz (Hz). The plural form was typically used, often written cycles per second, cycles/second, c.p.s., c/s, or, ambiguously, just cycles (Cy./Cyc.). The term comes from the fact that

sound wave In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

s have a frequency measurable in their number of oscillations, or ''

cycle Cycle, cycles, or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in soc ...

s'', per second. With the organization of the

International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...

in 1960, the cycle per second was officially replaced by the hertz, or reciprocal second, "s⁻¹" or "1/s". Symbolically, "cycle per second" units are "cycle/second", while hertz is "Hz" or "s⁻¹". For higher frequencies, ''kilocycles'' (kc), as an abbreviation of ''kilocycles per second'' were often used on components or devices. Other higher units like ''megacycle'' (Mc) and less commonly ''kilomegacycle'' (kMc) were used before 1960 and in some later documents. These have modern equivalents such as kilohertz (kHz), megahertz (MHz), and gigahertz (GHz). Following the introduction of the SI standard, use of these terms began to fall off in favor of the new unit, with hertz becoming the dominant convention in both academic and colloquial speech by the 1970s. The rate at which aperiodic or stochastic events occur may be expressed in becquerels (as in the case of

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), not hertz, since although the two are mathematically similar, by convention hertz implies regularity where becquerels implies the requirement of a time averaging operation. Thus, one becquerel is one event per second ''on average'', whereas one hertz is one event per second on a regular cycle. Cycle can also be a unit for measuring usage of reciprocating machines, especially presses, in which cases ''cycle'' refers to one complete revolution of the mechanism being measured (i.e. the shaft of a reciprocating engine). Derived units include cycles per day (cpd) and cycles per year (cpy).

References

{{reflist Units of frequency

See also

References