The metre (Commonwealth English [1]) or meter (American English [2]) (symbol: m) is the SI base unit of length. It is defined as the length of the path travelled by light [3] in absolute vacuum during a time [4] interval of 1/299,792,458 of a second [5].
Contents
SI prefixes applied to the metre[]
Adding SI prefixes to metre creates multiples and submultiples; for example kilometre (1000 metres; kilo- = 1000) and millimetre (one thousandth of a metre; milli- = 1 / 1 000).
The metre may be used with SI prefixes as shown.
Multiple | Name | Symbol | Multiple | Name | Symbol | |
---|---|---|---|---|---|---|
10^{0} | metre | m | ||||
10^{1} | decametre | dam | 10^{−1} | decimetre | dm | |
10^{2} | hectometre | hm | 10^{−2} | centimetre | cm | |
10^{3} | kilometre | km | 10^{−3} | millimetre | mm | |
10^{6} | megametre | Mm | 10^{−6} | micrometre | µm | |
10^{9} | gigametre | Gm | 10^{−9} | nanometre | nm | |
10^{12} | terametre | Tm | 10^{−12} | picometre | pm | |
10^{15} | petametre | Pm | 10^{−15} | femtometre | fm | |
10^{18} | exametre | Em | 10^{−18} | attometre | am | |
10^{21} | zettametre | Zm | 10^{−21} | zeptometre | zm | |
10^{24} | yottametre | Ym | 10^{−24} | yoctometre | ym |
Conversions[]
1 metre is equivalent to:
- exactly 1/0.9144 yards [6] (approximately 1.0936 yards)
- exactly 1/0.3048 feet [7](approximately 3.2808 feet)
- exactly 10000/254 inches [8] (approximately 39.370 inches)
History[]
See History at [9]
Timeline of definition[]
- May 8, 1790 — The National Assembly (French Revolution) [10] decides that the length of the new metre would be equal to the length of a pendulum with a half-period of one second.
- March 30, 1791 — The French National Assembly accepts the proposal by the French Academy of Sciences [11] that the new definition for the metre be equal to one ten-millionth of the length of the earth's meridian (geography)[12] along a quadrant (one-fourth the polar circumference of the earth).
- 1795 — Provisional metre bar constructed of brass [13].
- December 10, 1799 — The French National Assembly specifies that the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standard.
- September 28, 1889 — The first Conférence Générale des Poids et Mesures [14] defines the length as the distance between two lines on a standard bar of an alloy of platinum with ten percent iridium [15], measured at the melting point of ice.
- October 6, 1927 — The seventh CGPM adjusts the definition of the length to be the distance, at 0 °C, between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmospheric pressure [16] and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other.
- October 20, 1960 — The eleventh CGPM defines the length to be equal to 1,650,763.73 wavelengths [17] in vacuum of the electromagnetic radiation [18] corresponding to the transition between the 2p^{10} and 5d^{5} quantum levels of the krypton-86 atom.
- October 21, 1983 — The seventeenth CGPM defines the length to be distance travelled by light [19] in vacuum during a time interval of 1/299 792 458 of a second [20].
See also[]
- Metric system
- SI
- SI prefix
- Conversion of units for comparisons with other units
- Orders of magnitude (length)
- Speed of light
External links[]
- History of the metre at the U.S. National Institute of Standards and Technology (NIST)
- Timeline of history of the metre at the NIST
- Bureau International des Poids et Measures - Lengths
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