cycles

A cycle is a process or sequence of events that repeats itself, returning to its starting point after a period of time or after a set of conditions.

Biological cycles include life cycles, which describe stages organisms go through from birth to reproduction; circadian rhythms that govern daily physiological changes; and seasonal cycles tied to weather and food availability.

In geology and ecology, material cycles move elements through ecosystems and the environment. The water cycle involves evaporation, condensation, precipitation; the carbon cycle moves carbon through atmosphere, biosphere, oceans, and rocks via photosynthesis, respiration, decomposition, and weathering. The nitrogen cycle includes fixation, mineralization, nitrification, and denitrification.

Mechanics and mathematics use cycles to describe repeating motion and periodic phenomena. In engineering, the four-stroke cycle powers internal combustion engines. In physics, cycles describe oscillations and waves with a defined frequency. In mathematics, cycles can refer to cycle notation in permutations or to cyclic patterns in graphs and sequences.

Economic cycles refer to recurring phases of expansion and contraction in economic activity, with trade cycles, investment cycles, and technological cycles contributing to periodic fluctuations.

Understanding cycles helps in forecasting, resource management, and design. They are studied across disciplines with varying timescales.