Metre
From Engineering
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]].
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[edit] 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 | |
|---|---|---|---|---|---|---|
| 100 | metre | m | ||||
| 101 | decametre | dam | 10–1 | decimetre | dm | |
| 102 | hectometre | hm | 10–2 | centimetre | cm | |
| 103 | kilometre | km | 10–3 | millimetre | mm | |
| 106 | megametre | Mm | 10–6 | micrometre | µm | |
| 109 | gigametre | Gm | 10–9 | nanometre | nm | |
| 1012 | terametre | Tm | 10–12 | picometre | pm | |
| 1015 | petametre | Pm | 10–15 | femtometre | fm | |
| 1018 | exametre | Em | 10–18 | attometre | am | |
| 1021 | zettametre | Zm | 10–21 | zeptometre | zm | |
| 1024 | yottametre | Ym | 10–24 | yoctometre | ym |
[edit] 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)
[edit] History
See History at [[9]]
[edit] 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 2p10 and 5d5 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]].
[edit] See also
- Metric system
- SI
- SI prefix
- Conversion of units for comparisons with other units
- Orders of magnitude (length)
- Speed of light
[edit] 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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