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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. The exact modern SI definition is " [The second] is ...
The unit is used to measure the length of the Harvard Bridge. Canonically, and originally, in 1958 when Smoot was a Lambda Chi Alpha pledge at MIT (class of 1962), the bridge was measured to be 364.4 Smoots, plus or minus one ear, using Mr. Smoot himself as a ruler. [19] At the time, Smoot was 5 feet, 7 inches, or 170 cm, tall. [20]
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]
In astrophysics and quantum physics a jiffy is, as defined by Edward R. Harrison, [ 13] the time it takes for light to travel one fermi, which is approximately the size of a nucleon. One fermi is 10−15 m, so a jiffy is about 3 × 10−24 s. It has also more informally been defined as "one light-foot", which is equal to approximately one ...
This was an official unit of measurement in South Africa until the 1970s, and was defined in November 2007 by the South African Law Society as having a conversion factor of 1 morgen = 0.856 532 hectares. [25] This unit of measure was also used in the Dutch colonial province of New Netherland (later New York and parts of New England). [26] [27]
10−15 s. A femtosecond is a unit of time in the International System of Units (SI) equal to 10 −15 or 1⁄1 000 000 000 000 000 of a second; that is, one quadrillionth, or one millionth of one billionth, of a second. [ 1] For context, a femtosecond is to a second as a second is to about 31.71 million years; a ray of light travels ...
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million ( ppm ...
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.