Hertz Hertz The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (10 Hz, kHz), megahertz (10 Hz, MHz), gigahertz (10 Hz, GHz), terahertz (10 Hz, THz), petahertz (10 Hz, PHz), and exahertz (10 Hz, EHz). Some of the unit's most common uses are in the description of sine waves and musical tones, particularly those used in radio- and
Revolutions per minute Revolutions per minute Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min) is the number of turns in one minute. It is a unit of rotational speed or the frequency of rotation around a fixed axis. According to the International System of Units (SI), rpm is not a unit. This is because the word "revolution" is a semantic annotation rather than a unit. The annotation is instead done as a subscript of the formula sign if needed. Because of the measured physical quantity, the formula sign has to be for (rotational) frequency and or for angular