Periodicity is the quality of occurring at regular intervals or periods (in time or space) and can occur in different contexts:

In timing devices:

• A clock marks time at periodic intervals.
• A metronome ticks at periodic intervals of time.

In science:

• The measure of periodicity in time is frequency which has the metric units of Hertz.
• Oscillations, waves and standing waves have crests at periodic intervals of space and/or time.
• In physics, period is the number of cycles as a result of time (time/cycle). The amount of time it takes to complete one full revolution. Period is also the inverse of frequency.
• In mathematics, a periodic function is a function whose output contains values that repeat periodically.
• In mathematics, in group theory, a periodic group is a group in which each element has finite order.
• In chemistry, the periodic table is a table which classifies the chemical elements by means of the periodicity of their chemical properties.

Other uses:

• In finance, the periodicity of a loan describes the interval between payments.
• A publication published at periodic intervals can be called a "periodical", for example a magazine.
• In music theory, periodicity is described as "predictability gives rise to expectations".

See also

• Cycle
• Frequency (disambiguation)
• Seasonality
• Simultaneity
• Synchronicity
• Utility frequency

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