Frequency rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter "f" or by the Greek letter "formula_1" or "ν" (nu) (see e.g. Planck's formula). The relation between the frequency and the period formula_2of a repeating event or oscillation is given by The SI derived unit of frequency is the hertz (Hz), named after the
Angular frequency for the vector quantity angular velocity. One revolution is equal to 2π radians, hence where ω is referred to as the natural frequency (which can sometimes be denoted as ω). As the object oscillates, its acceleration can be calculated by where "x" is displacement from an equilibrium position. Using "ordinary" revolutions-per-second frequency, this equation would be The resonant angular frequency in a series LC circuit equals the square root of the reciprocal of the product of the capacitance ("C" measured in farads) and the inductance of the circuit ("L", with SI unit henry): Adding series resistance (for example, due to