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A unit of time is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI), and by extension most of the Western world , is the second , defined as about 9 billion oscillations of the caesium atom.
It is the unit of time in the natural units system known as Planck units. 10 −30: quectosecond: qs Quectosecond, (quecto-+ second), is one nonillionth of a second 10 −27: rontosecond: rs Rontosecond, (ronto-+ second), is one octillionth of a second 300 rs: The mean lifetime of W and Z bosons: 10 −24: yoctosecond: ys [4]
The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each ...
The earliest technical usage for jiffy was defined by Gilbert Newton Lewis (1875–1946). He proposed in 1926 a unit of time called the "jiffy" which was equal to the time it takes light to travel one centimeter in vacuum (approximately 33.3564 picoseconds). [5]
Metric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other units of time – minute, hour, and day – are accepted for use with SI, but are not part of it
In the International System of Units (SI), the unit of time is the second (symbol: s). It has been defined since 1967 as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and is an SI base unit. [12]
"The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, ∆ ν Cs , the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom , to be 9 192 631 770 when expressed in the unit Hz, which is equal to s −1 ."
The second, symbol s, is the SI unit of time. ... the definition of every base unit except the mole and almost every derived unit relies on the definition of the second.