Fréquence

Fréquence, or frequency, is the rate at which something occurs or repeats over a given period of time. In physics and engineering, it typically refers to the number of cycles of a periodic process per unit time, most often expressed in hertz (Hz), where 1 Hz equals one cycle per second. The angular frequency, measured in radians per second, is related by ω = 2πf.

The reciprocal of frequency is the period: f = 1/T, where T is the time required for one complete cycle. For waves, frequency is linked to speed and wavelength by the relation f = v/λ, where v is the wave speed and λ its wavelength. Higher frequency waves have shorter wavelengths at a given speed. In acoustics, frequency largely determines pitch; in optics, it relates to color or photon energy.

In signal processing and data analysis, frequency describes the distribution of a signal’s energy across different frequency components. Fourier analysis decomposes a signal into sinusoidal components, revealing its spectrum. When sampling a continuous signal, the sampling frequency must be at least twice the highest frequency present (the Nyquist limit) to avoid aliasing.

Statistically and in linguistics, frequency denotes how often an event or item occurs within a dataset or corpus. Relative frequency expresses this as a proportion of total observations. In everyday use, frequency can describe anything from the occurrence of events (monthly meetings) to the rate of heartbeats or traffic signals, each with domain-specific conventions and measurement scales.