2. Mathematical cycle: The time required for sine alternating current to complete a cycle change is called cycle, which is expressed in letters and the unit is seconds (s). Obviously, the time interval between two adjacent maxima (or two adjacent minima) of sinusoidal alternating current or voltage is a period.
3. Chemical cycle: refers to a series of elements with the same number of electronic layers and arranged in the order of increasing atomic number. The periodic table of elements has seven rows, that is, seven periods. The first, second and third periods are called short periods; The fourth, fifth, sixth and seventh periods are called long periods; Generally, each cycle begins with active metallic elements, gradually transitions to active nonmetallic elements, and finally ends with rare gas elements.
4. Physical cycle: Uniform circular motion is a kind of periodic motion. The so-called periodicity means that the moving object returns to its original position repeatedly after a certain period of time, and the instantaneous speed also returns to its original size and direction repeatedly. The time required for an object to make a uniform circular motion is called a period. The period is represented by symbol T, which is also a physical quantity describing the speed of uniform circular motion. A long period means that the object moves slowly, and a short period means that the object moves fast.
5. Biological cycle: The spontaneous or biological passive activity of the object itself is called a cycle from beginning to end, such as the movement of celestial bodies, and the earth rotates around the sun for one year. Biological cell division, from cell preparation to division, goes through prophase, metaphase, anaphase and anaphase, and finally returns to interphase, which is a cycle. The process of a simple pendulum sliding from the highest point to the lowest point and then back to the starting point is called a cycle.
6. Economic cycle: Economic cycle, also known as business cycle and boom cycle, refers to the phenomenon that economic expansion and economic contraction alternate and cycle periodically in economic operation. It is the fluctuation of total national output, total income and total employment, and it is the alternating or periodic fluctuation of expansion and contraction of national income or overall economic activities. The past is divided into four stages: prosperity, recession, depression and recovery. Now it is generally called recession, trough, expansion and peak.