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Frequency (symbol f), most often measured in hertz (symbol: Hz), is the number of occurrences of a repeating event per unit of time. [1] It is also occasionally referred to as temporal frequency for clarity and to distinguish it from spatial frequency.
Its SI unit is the reciprocal seconds (s −1); other common units of measurement include the hertz (Hz), cycles per second (cps), and revolutions per minute (rpm). [ 1 ] [ a ] [ b ] Rotational frequency can be obtained dividing angular frequency , ω, by a full turn (2 π radians ): ν =ω/(2π rad).
≈ 0.0167 Hz: cycle per second: cps ≡ 1 Hz = 1 cps = 1 Hz degree per second: deg/s ≡ 1 °/s ≡ 1/360 Hz = 0.002 7 Hz hertz (SI unit) Hz ≡ One cycle per second = 1 Hz = 1/s radian per second: rad/s ≡ 1/(2π) Hz ≈ 0.159 155 Hz: revolution per minute: rpm ≡ One rpm equals one rotation completed around a fixed axis in one minute of time.
50 milliseconds – cycle time for the lowest audible tone, 20 Hz; 60 milliseconds – cycle time for European 16.7 Hz AC electrified railroad power grid; 60 milliseconds – the time interval between gear changes on a Ferrari 458 Spider; with a 7-speed dual-clutch automatic transmission; 62.5 milliseconds – a sixty-fourth note at 60 BPM
Subdivisions of the day include the hour (1/24 of a day), which is further subdivided into minutes and seconds. The second is the international standard unit (SI unit) for science. Celestial sphere-based: as in sidereal time, where the apparent movement of the stars and constellations across the sky is used to calculate the length of a year.
Atomic clocks usually have an external PPS output, although internally they may operate at 9,192,631,770 Hz. [3] PPS signals have an accuracy ranging from 12 picoseconds to a few microseconds per second, or 2.0 nanoseconds to a few milliseconds per day based on the resolution and accuracy of the device generating the signal.
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. [ 1 ] [ a ] The hertz is an SI derived unit whose formal expression in terms of SI base units is s −1 , meaning that one hertz is one per second or the reciprocal of one second . [ 2 ]
1.67 minutes (or 1 minute 40 seconds) 10 3: kilosecond: 1 000: 16.7 minutes (or 16 minutes and 40 seconds) 10 6: megasecond: 1 000 000: 11.6 days (or 11 days, 13 hours, 46 minutes and 40 seconds) 10 9: gigasecond: 1 000 000 000: 31.7 years (or 31 years, 252 days, 1 hour, 46 minutes, 40 seconds, assuming that there are 7 leap years in the interval)