Metre

The or meter ( from Ancient Greek μέτρον métron, dimension ',' tool for measuring ',' length ') is the basic unit of length in the International System of Units (SI ) and other metric systems of units.

The meter should be the ten -millionth of the distance from the North Pole to the equator at sea level originally. Since 1983, a meter is defined as the distance traveled by light in vacuum during a time of 1 / 299,792,458 seconds. The unit symbol of the meter is the small letter " m ". For decimal multiples and parts of the international resolutions for units of measurement.

Definition history

The length unit meters in use since the late 18th century. The origin of this length unit goes back to a decision of the French National Assembly, to define a uniform measure. The were some proposals for the definition of a unit of length ahead, which was not derived different from the traditional linear dimensions of the length of human limbs ( the finger width, the customs, the hand width, hand span, the cubit, the foot, the step and the fathoms ). So hit the abbot Jean Picard in 1668 as a unit of length, the second pendulum ago - that is, the length of a pendulum, which has a half- period of one second. In the gravitational field of Europe such a pendulum would have the length of about 0,994 m and would today's definition of a meter pretty close.

Decisive for the new unit of length, however, was not the seconds pendulum, but the figure of the earth. 1735 the Paris Academy of Sciences sent two expeditions to the measurement of a degree in today's Ecuador and to Lapland to determine the exact dimensions of the earth. In 1793 began the French National Convention - in addition to a new calendar - a new measure of length that: The meter should be the 10 millionth part of the earth's quadrant on the meridian of Paris - that is, the ten millionth of the distance from the North Pole via Paris to the equator. A prototype of this meter in 1795 cast brass. He later proved to be extremely accurate - as measured by the ambitious goal he was only 0.013 % or 0.13 millimeters too long.

Between 1792 and 1799, certain Delambre and Méchain the length of the arc of the meridian between Dunkirk and Barcelona again. From a combination of the Ecuador - Lapland results, a new value to 443.296 lines of Paris, which was made ​​mandatory in 1799 and is recognized as a platinum rod, the standard meter was. In the 19th century, however, were more accurate measurements of the earth to the conclusion that the standard meter was advised about 0.02 % too short. Nevertheless, it was held on the meter defined in 1799 - with the result that the Erdmeridianquadrant not exceed 10 000 km 10 but 001,966 km long. This length applies to the meridian of Paris, other meridians may have different lengths. A side effect was that it was realized that the earth is not exactly spherical, but has an irregular shape. The earth had thus proved to be unsuitable for the definition of the meter. By 1960, therefore, the meter was fixed as the length of a concrete object - the first standard meter, since 1889 then the International prototype meter ( see below). All subsequent definitions had to meet the goal of this length as accurately as possible.

The North German Confederation decided on August 17, 1868, the introduction of the French meter system on January 1, 1872. Belonged to Germany in 1875 to the twelve founding members of the Metre Convention.

In 1889, the International Bureau of Weights and Measures led ( BIPM) the standard meter as a prototype for the unity of a meter. It was a rod of cruciform cross section. As a material, a platinum -iridium alloy in the ratio of 90:10 was chosen. The length of the meter was defined as the distance between the center lines of two groups of lines on the rod held at a constant temperature of 0 ° C. There were thirty copies of this prototype produced and handed over to national calibration Institute.

Although great emphasis was placed on durability and immutability in the production of prototypes meters, it was clear that these are fundamentally impermanent. Any copying inevitably led to the risk of differences and - just like regular comparisons of copies with each other and with the original - the risk of damage.

To remedy this, in 1960 set: One meter is the 1 650 763.73 times the wavelength of the atoms of the nuclide 86Kr in the transition from state to state 5d5 2p10 emitted, propagating in the vacuum radiation. Understanding this definition is only knowledge in atomic physics ahead. If these and the necessary equipment is available, the length can be reproduced by a meter at any location. Instead of the physical scale to be stored, the standard meter, based the definition of the meter since then on a test specification for natural constants that can be measured independently of material measures. The number has been chosen so that the result corresponded to the valid to 1960 meters within the then measurement accuracy.

Improvements in measurement accuracy in the realization of the meter under this provision changed respectively to the numerical value of the fundamental constant speed of light in empty space. Recently this happened in 1973. At the 15th General Conference on Weights and Measures ( CGPM short ) it was decided to consider the numerical value of the vacuum speed of light as a constant. In return, it has been proposed to define the length of a meter than that range, the light passes through the vacuum within the time interval of 1 / 299,792,458 seconds. The 17th CGPM adopted this definition, on 20 October 1983.

Common decimal multiples

The meter unit is equipped with various decimal multiples (also SI prefixes ) in use, for example:

Compositions with other prefixes are uncommon.

Conjunction with other common units of length

Usage

The German unit name "meter " comes from French mètre [ from Latin metrum, Greek métron = ( verse ) dimension, syllabic ].

The unit name "meter" was mainly used to DIN 1301-1. This notation, however, no longer coincided with the common linguistic use. In particular, the dictionary makes the neuter form to only second. The DIN 1301-1:2010-10 this setting has been changed from the DIN 1301-1:2002-10; Name of the unit "meter" is now defined as a male.

As to whether the unit is meters flexed or used in single or multiple, you can according to Duden distinguish the following cases:

• Is that the measure whereof is given, directly behind the unit the endung loose form " in height of 2 meters " or " in 100 meters "
• Is that the measure whereof is given, not directly behind the unit of measurement, usually in the form of the inflectional ending is used:

• The inflectional ending is also used when the number and the value to another article joined " with the 150 m walk " or " neglect of a meter ."