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Encyclopedia > Meter

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 absolute vacuum during a time interval of 1/299,792,458 of a second. The SI system of units defines seven SI base units: fundamental physical units defined by an operational definition. ... In general English usage, length (symbols: l, L) is but one particular instance of distance â€“ an objects length is how long the object is â€“ but in the physical sciences and engineering, the word length is in some contexts used synonymously with distance. Height is vertical distance; width (or breadth... In general English usage, length (symbols: l, L) is but one particular instance of distance â€“ an objects length is how long the object is â€“ but in the physical sciences and engineering, the word length is in some contexts used synonymously with distance. Height is vertical distance; width (or breadth... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ... For other uses, see vacuum cleaner and Vacuum (musical group). ... 8:17 am, August 6, 1945, Japanese time. ... The second (symbol s) is a unit for time, and one of seven SI base units. ...

Adding SI prefixes to metre creates multiples and submultiples; for example kilometre (1000 metres; kilo- = 1000) and nanometre (one billionth of a metre; nano- = 1 / 1 000 000 000). An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ... The word billion and its equivalents in other languages refer to one of two different numbers. ...

## Contents

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

The word itself is from the Greek metron (μετρον), "a measure" via the French mètre. Its first recorded usage in English is from 1797. Measure can mean: To perform a measurement. ... The English language is a West Germanic language that originates in England. ...

In the eighteenth 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 of one second. The other suggested defining the metre as one ten-millionth of the length of the earth's 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. Simple Gravity Pendulum assumues no air resistance and no friction of/at the nail/screw. ... Periodicity is the quality of occurring at regular intervals (e. ... The second (symbol s) is a unit for time, and one of seven SI base units. ... On the earth, a meridian is a north-south line between the North Pole and the South Pole. ... The French Academy of Sciences (AcadÃ©mie des sciences) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. ... It has been suggested that Law of universal gravitation be merged into this article or section. ... Earth, also known as the Earth, Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ...

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.

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: 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. Template:USgov Template:Nist http://www. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Atomic mass 83. ... Cherenkov effect in a swimming pool nuclear reactor. ... The Metre Convention (or Convention of the Metre, or Convention du Mètre in French, its original language) of 1875 is an international treaty that established what is now known as the SI system. ... The Bureau International des Poids et Mesures (International Bureau of Weights and Measures, or BIPM) is a standards organization, one of the three organizations established to maintain the SI system under the terms of the Metre Convention. ... Road to SÃ¨vres, Jean-Baptiste Camille Corot, 1855-1865. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... The General Conference on Weights and Measures is the English name of the ConfÃ©rence gÃ©nÃ©rale des poids et mesures (CGPM, sometimes written in English ConfÃ©rence GÃ©nÃ©rale des Poids et Mesures). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... General Name, Symbol, Number iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Appearance silvery white Atomic mass 192. ...

In 1893, the standard metre was first measured with an interferometer by 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 CGPM defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the 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. Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... Albert Abraham Michelson. ... The wavelength is the distance between repeating units of a wave pattern. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... The General Conference on Weights and Measures is the English name of the ConfÃ©rence gÃ©nÃ©rale des poids et mesures (CGPM, sometimes written in English ConfÃ©rence GÃ©nÃ©rale des Poids et Mesures). ... The International System of Units (abbreviated SI from the French phrase, SystÃ¨me International dUnitÃ©s) is the most widely used system of units. ... The wavelength is the distance between repeating units of a wave pattern. ... The colour orange occurs between red and yellow in the visible spectrum at a wavelength of about 620–585 nanometres. ... Red is a color at the lowest frequencies of light discernible by the human eye. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... The electromagnetic spectrum is the range of all possible electromagnetic radiation. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Atomic mass 83. ... Properties For alternative meanings see atom (disambiguation). ... For other uses, see vacuum cleaner and Vacuum (musical group). ...

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: 8:17 am, August 6, 1945, Japanese time. ... Cherenkov effect in a swimming pool nuclear reactor. ...

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

• 1795 — Provisional metre bar constructed of brass.
• 1799 December 10 — The French National Assembly specifies that the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standards.
• 1889 September 28 — The first 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.
• 1927 October 6 — 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 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.
• 1960 October 20 — The eleventh CGPM defines the length to be equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.
• 1983 October 21 — 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.

## SI multiples

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

The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... The International System of Units (abbreviated SI from the French phrase, SystÃ¨me International dUnitÃ©s) is the most widely used system of units. ... An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ... This article lists conversion factors between a number of units of measurement. ... Categories: Orders of magnitude (length) | Length ...

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