Although the historical definition of the unit was based on this division of the Earth's rotation cycle, the formal definition in the International System of Units (SI) is a much steadier timekeeper: it is defined by taking the fixed numerical value of the caesium frequency ∆νCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1. Many derivative units for everyday things are reported in terms of larger units of time, not seconds, such as clock time in hours and minutes, velocity of a car in kilometers per hour or miles per hour, kilowatt hours of electricity usage, and speed of a turntable in rotations per minute. "[12] BAAS formally proposed the CGS system in 1874, although this system was gradually replaced over the next 70 years by MKS units. Multiples of seconds are usually expressed as minutes and seconds, or hours, minutes and seconds of clock time, separated by colons, such as 11:23:24, or 45:23 (the latter notation can give rise to ambiguity, because the same notation is used to denote hours and minutes). Il convient de rappeler que 1°, 2° ; 3°... sont les abréviations de primo, secundo, tertio... le signe supérieur étant un o et non un zéro.

In 1579, Jost Bürgi built a clock for William of Hesse that marked seconds. Some common events in seconds are: a stone falls about 4.9 meters from rest in one second; a pendulum of length about one meter has a swing of one second, so pendulum clocks have pendulums about a meter long; the fastest human sprinters run 10 meters in a second; an ocean wave in deep water travels about 23 meters in one second; sound travels about 343 meters in one second in air; light takes 1.3 seconds to reach Earth from the surface of the Moon, a distance of 384,400 kilometers. Liste des abréviations courantes : “2d... Toutes les abréviations du mot second.
Fractions of a second are usually counted in tenths or hundredths. Metrologists also knew that Earth's orbit around the Sun (a year) was much more stable than earth's rotation. [16], SI prefixes are commonly used for times shorter than one second, but rarely for multiples of a second. » Abbreviations.com. But a sundial which measures the relative position of the sun in the sky called apparent time, does not keep uniform time. The second was thus defined as "the fraction ​1⁄31,556,925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time". For other uses, see, Sexagesimal divisions of calendar time and day. Conceptual units of time smaller than realizable on sundials were also used. This led to proposals as early as 1950 to define the second as a fraction of a year. The Earth's motion was described in Newcomb's Tables of the Sun (1895), which provided a formula for estimating the motion of the Sun relative to the epoch 1900 based on astronomical observations made between 1750 and 1892. Analog clocks and watches often have sixty tick marks on their faces, representing seconds (and minutes), and a "second hand" to mark the passage of time in seconds.

Atomic clocks use such a frequency to measure seconds by counting cycles per second at that frequency. We're doing our best to make sure our content is useful, accurate and safe.If by any chance you spot an inappropriate comment while navigating through our website please use this form to let us know, and we'll take care of it shortly. Se dit de la deuxième division d'un ouvrage : Chapitre second. In 1832, Gauss proposed using the second as the base unit of time in his millimeter-milligram-second system of units. Mechanical clocks kept the mean time, as opposed to the apparent time displayed by sundials. Both the CGS and MKS systems used the same second as their base unit of time. [13] This definition was adopted as part of the International System of Units in 1960.[15]. [1][2] Digital clocks and watches … The second (symbol: s, abbreviation: sec) is the base unit of time in the International System of Units (SI) (French: Système International d’unités), commonly understood and historically defined as ​1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

The meter is defined in terms of the speed of light and the second; definitions of the metric base units kilogram, ampere, kelvin, and candela also depend on the second. La tradition veut qu’on emploie « deuxième » lorsque l’énumération peut aller au-delà de deux, et « second » lorsque l’énumération s’arrête à deux. Cette distinction n’est pas toujours observée et certains écrivent indifféremment « deuxième » ou « second ». « Abréviation des noms ordinaux : on abrègera première, deuxième, troisième... : 1re, 2e, 3e, et non 1 ère, 2 ème ou 3 ème. » Second, twelfth, twenty-second, thirty-second, … Deuxième, douzième, vingt-deuxième, trente-deuxième, … Abréviations [modifier le wikicode] 2nd; II (monarque) Dérivés [modifier le wikicode] second nature (seconde nature) Adverbe [modifier le wikicode] second \ˈsɛk.ənd\ Deuxièmement, secundo. Far better for timekeeping is the natural and exact "vibration" in an energized atom.
Because the Earth's rotation varies and is also slowing ever so slightly, a leap second is periodically added to clock time[nb 1] to keep clocks in sync with Earth's rotation. [nb 2][nb 3], The earliest mechanical clocks which appeared starting in the 14th century had displays that divided the hour into halves, thirds, quarters and sometimes even 12 parts, but never by 60. The difference between apparent solar time and mean time was recognized by astronomers since antiquity, but prior to the invention of accurate mechanical clocks in the mid-17th century, sundials were the only reliable timepieces, and apparent solar time was the generally accepted standard. . It had a pendulum length of just under a meter which gave it a swing of one second, and an escapement that ticked every second. [13] This resulted in adoption of an ephemeris time scale expressed in units of the sidereal year at that epoch by the IAU in 1952. The second (symbol: s, abbreviation: sec) is the base unit of time in the International System of Units (SI) (French: Système International d’unités), commonly understood and historically defined as ​ ⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each. [9]:417–418[10] During the 3rd quarter of the 16th century, Taqi al-Din built a clock with marks every 1/5 minute. [3], Civil time is defined to agree with the rotation of the earth. A mechanical clock, one which does not depend on measuring the relative rotational position of the earth, keeps uniform time called mean time, within whatever accuracy is intrinsic to it. The British Association for the Advancement of Science (BAAS) in 1862 stated that "All men of science are agreed to use the second of mean solar time as the unit of time. Get instant explanation for any acronym or abbreviation that hits you anywhere on the web. STANDS4 LLC, 2020. Fractions of a second are usually denoted in decimal notation, for example 2.01 seconds, or two and one hundredth seconds. While they are not yet part of any timekeeping standard, optical lattice clocks with frequencies in the visible light spectrum now exist and are the most accurate timekeepers of all. Qui vient après le premier dans une succession, un ensemble ordonné, une classification : Le second volume paraîtra dans six mois. Sexagesimal divisions of the day from a calendar based on astronomical observation have existed since the third millennium BC, though they were not seconds as we know them today[citation needed]. The current generation of atomic clocks is accurate to within one second in a few hundred million years. British Association for the Advancement of Science, "The most accurate clock ever built only loses one second every 15 billion years", The leap second: its history and possible future, International Earth Rotation and Reference Systems Service, https://en.wikipedia.org/w/index.php?title=Second&oldid=982510520, Short description is different from Wikidata, All Wikipedia articles written in American English, Articles with unsourced statements from January 2020, Creative Commons Attribution-ShareAlike License, This page was last edited on 8 October 2020, at 16:14. Some time in the late 1940s, quartz crystal oscillator clocks with an operating frequency of ~100 kHz advanced to keep time with accuracy better than 1 part in 108 over an operating period of a day. The second is also part of several other units of measurement like meters per second for velocity, meters per second per second for acceleration, and cycles per second for frequency. Web. TAI "ticks" atomic seconds. This time scale "ticks" the same atomic seconds as TAI, but inserts or omits leap seconds as necessary to correct for variations in the rate of rotation of the earth.[4].

"Second." A set of atomic clocks throughout the world keeps time by consensus: the clocks "vote" on the correct time, and all voting clocks are steered to agree with the consensus, which is called International Atomic Time (TAI). Digital clocks and watches often have a two-digit seconds counter. There are references to 'second' as part of a lunar month in the writings of natural philosophers of the Middle Ages, which were mathematical subdivisions that could not be measured mechanically. [17], This article is about the unit of clock time. Multiples of seconds are usually counted in hours and minutes. Explication de Bernard Cerquiglini en images, Dictionnaire de l’Académie française, huitième édition, https://fr.wiktionary.org/w/index.php?title=second&oldid=28645471, Mots en anglais issus d’un mot en ancien français, Wiktionnaire:Prononciations phonétiques manquantes en français, Wiktionnaire:Prononciations phonétiques manquantes en anglais, licence Creative Commons attribution partage à l’identique, « Second » et « deuxième » ont le même sens, seul l’usage diffère : les grammairiens et l’. So a clock with 60 divisions would have a mark for thirds, fourths, fifths, sixths and twelfths (the hours); whatever units the clock would likely keep time in, would have marks. Such a clock can measure a change in its elevation of as little as 2 cm by the change in its rate due to gravitational time dilation.[6]. Je cherche l'abréviation de “second” ? (+ superlatif) Le deuxième plus. For the metric unit of second, there are decimal prefixes representing 10−24 to 1024 seconds.


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