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Metre
*** Shopping-Tip: Metre
:''This article is about the unit of length. For other uses of ''metre'', see ''
meter (disambiguation)''.''
The '''Metre''' (or '''Meter''') is the base
fundamental unit of length in the
metric system metric systems of measurement measurement system as defined originally by the '''French Academy of Sciences''' during the French Revolutionary–Napoleonic war era, and subsequently adopted by various successive '''International Standards Committees''' as the utility, elegance, and self-consistency of the system led to wider acceptance and use. It was initially accepted only among the world's
Physical sciences physical scientists and then followed by engineers and other technical specialists, but was spurned by the public at large who were wedded to their
traditional measurement systems. It is not accidental or unrelated that the growth of science and technology grew hand-in-hand with the spread and use of the
system, as the system utilises a series of
suffixes related to multiples of ten and
exponents powers of ten, giving extreme ease of
scaling and
conversion, which being calculation intensive, are much more prone to error in less regularised systems.
*In the
United States '''meter''' is the common spelling of this otherwise world wide term. See:
American and British English differences .
Image:Platinum-Iridium meter bar.jpg right|frame|''International Prototype Metre'' standard bar made of platinum-iridium. This was the standard until 1960, when the new SI system used a [[krypton-spectrum measurement as the base. In 1983 the current metre was defined by a relationship to the
speed of light in a vacuum.]]
Basics
The '''metre''' or '''meter''' (symbol: m) is the
SI base unit of
length. It is defined as the
length of the path travelled by
light in an absolute
vacuum during a
time interval of 1/299,792,458 of a
second.
Adding
SI prefixes to ''metre'' creates multiples and submultiples; for example ''kilometre'' (1000 metres; ''kilo-'' = 1000) and ''millimetre'' (one
Thousand thousandth of a metre; ''milli-'' = 1 / 1000).
SI prefixes applied to the metre
The metre may be used with
SI prefixes.
{|class="wikitable"
! 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
Since 1958, 1 metre is equivalent to:
* exactly 1/0.9144
yards (approximately 1.0936 yards)
* exactly 1/0.3048
feet (approximately 3.2808 feet)
* exactly 10000/254
inches (approximately 39.370 inches)
History
blarg
The word ''metre'' is from the
Greek language Greek ''metron'' (μετÏ?ον), "a
measure" via the
French language French ''mètre''. Its first recorded usage in
English language English is from 1797.
In the 18th century, there were two favoured approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a
pendulum with a half-
period (physics) period of one
second. The other suggested defining the metre as one ten-millionth of the length of the Earth's
meridian (geography) meridian along a quadrant (one-fourth the polar circumference of the Earth). In 1791, the
French Academy of Sciences selected the meridional definition over the pendular definition because of the slight variation of the force of
gravity over the surface of the earth, which affects the period of a pendulum. In 1793, France adopted the metre, with this definition, as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the earth, this length became the standard. So, the circumference of the
Earth through the poles is approximately forty million metres.
In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The
Metre Convention (Convention du Mètre) of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM:
Bureau International des Poids et Mesures) to be located in
Sèvres, France. This new organisation would preserve the new prototype metre and
kilogram when constructed, distribute national metric prototypes, and would maintain comparisons between them and non-metric measurement standards. This organisation created a new prototype bar in 1889 at the first General Conference on Weights and Measures (CGPM:
General Conference on Weights and Measures Conférence Générale des Poids et Mesures), establishing the ''International Prototype Metre'' as the distance between two lines on a standard bar of an alloy of ninety percent
platinum and ten percent
iridium, measured at the melting point of ice.
The New Improved Standard
In 1893, the standard metre was first measured with an
interferometer by
Albert Abraham Michelson Albert A. Michelson, the inventor of the device and an advocate of using some particular
wavelength of
light as a standard of distance. By 1925,
interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh
General Conference on Weights and Measures CGPM defined the metre in the new
SI system as equal to 1,650,763.73
wavelengths of the
orange (colour) orange-
red emission line in the
electromagnetic spectrum of the
krypton-86
atom in a
vacuum. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.
To further reduce uncertainty, the seventeenth CGPM of 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of
time and the
speed of light:
:''The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.''
Note that this definition exactly fixes the speed of light in a vacuum at 299,792,458 metres per second. Definitions based on the physical properties of light are more precise and reproducible because the properties of light are considered to be universally constant.
Timeline of definition
*
May 8 1790 — The
National Assembly (French Revolution) French National Assembly decides that the length of the new metre would be equal to the length of a
pendulum with a half-
period (physics) period of one
second.
*
March 30 1791 — The French National Assembly accepts the proposal by the
French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of the Earth's
meridian (geography) meridian along a quadrant (one-fourth the polar circumference of the Earth), that is, the distance from either pole to the equator .
*
1795 — Provisional metre bar constructed of
brass.
*
December 10 1799 — The French National Assembly specifies that the platinum metre bar, constructed on
23 June 1799 and deposited in the
National Archives of France National Archives, as the final standard.
*
September 28 1889 — The first
General Conference on Weights and Measures CGPM defines the length as the distance between two lines on a standard bar of an alloy of
platinum with ten percent
iridium, 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 °
Celsius 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 atmosphere of pressure 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 in
vacuum of the
electromagnetic radiation radiation 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 in vacuum during a time interval of 1/299 792 458 of a
second.
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
Category:Measurement
Category:Length
Category:history
Category:SI base units
Category:Units of length
af:Meter
als:Meter
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ast:Metru
bg:Метър
ca:Metre
cs:Metr
da:Meter
de:Meter
et:Meeter
el:ÎœÎÏ„Ï?ο (μονάδα μήκους)
es:Metro
eo:Metro
eu:Metro
fr:Mètre
gl:Metro
ko:미터
hr:Metar
id:Meter
ia:Metro
is:Metri
it:Metro
he:מטר
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lv:Metrs
lb:Meter
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ms:Meter
nl:Meter
ja:メートル
no:Meter
nn:Meter
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pt:Metro
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ru:Метр
sco:Metre
sq:Metri
simple:Metre
sk:Meter
sl:Meter
sr:Метар
su:Méter
fi:Metri
sv:Meter
ta:மீட�டர�
th:เมตร
vi:Mét
tr:Metre
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