Meters
Abbreviation/Symbol:
m
Unit of:
Worldwide use:
The metre, as part of the metric system, is used as a measure of distance across the globe, the primary exception being the United States, where the imperial system is used for most purposes.
The meter (m) is the SI base unit of length, defined since 1983 as the distance light travels in a vacuum in 1/299,792,458 of a second. It is 39.37 inches.
Every other metric length is the meter with a prefix on it: a centimeter is 0.01m, a millimeter 0.001m and a kilometer 1,000m.
Most countries give room sizes and people's heights in meters – 1.80m is about 5ft 11in. Sprint races are named for them too, as in the 100 meters.
Definition:
The meter is a fundamental unit of length in the International System of Units (SI). Since 1983, it has been defined as the distance traveled by light in a vacuum during a specific time interval. More precisely, the meter is defined as the length of the path traveled by light in a vacuum in 1/299,792,458 of a second. This definition was established in 1983 by the General Conference on Weights and Measures (CGPM) and is based on the speed of light, which is a universal constant.
1 m is equivalent to 1.0936 yards, or 39.370 inches.
Defining the meter from the speed of light (299,792,458 m/s) means it can be reproduced in any suitable laboratory, rather than copied from a metal bar.
Origin:
A decimal-based unit of measurement had been proposed as early as the late 17th century, with the name metre being derived from the Greek métron katholikón, meaning 'universal measure'.
An early definition of a metre was "the length of a pendulum with a half-period of one second" By the 18th century a definition based on "one ten-millionth of the length of the Earth's meridian along one quadrant" (the distance from the equator to the North Pole) was gaining favour, and this was the accepted definition when France adopted the metric system in 1795.
Prototype metre bars - first brass, later platinum then a platinum/iridium alloy - were manufactured as successive standards of the metre. In 1960 the metre was redefined using the wavelengths of radiation, before the current definition, relating the metre to the speed of light, was adopted in 1983.
To determine the length of the meter, the French Academy of Sciences turned to the Earth itself. They decided to use one ten-millionth of the distance from the North Pole to the equator as the basis for the meter. This distance was measured along a meridian passing through Paris, from Dunkirk to Barcelona. The task of accurately measuring this distance fell to two French astronomers, Jean-Baptiste Delambre and Pierre Méchain.
Delambre and Méchain spent several years surveying the meridian arc through Paris, working against difficult terrain, bad weather and the limits of their instruments. They presented their results in 1799.
The meter was then fixed as one ten-millionth of the distance from the North Pole to the equator (actually the Earth's quadrant is about 10,002km, so it came out about 0.2mm short of its own definition). It has since been redefined against the speed of light in a vacuum.
Common references:
A human male of average height is around 1.75 m tall.
The hurdles used in Olympic 110 m hurdles races are 1.067 m high.
The tallest building in the world (as of 2012), the Burj Khalifa in Dubai, is 828 m tall.
The Empire State Building in New York City is 381 m high.
The standard gauge of railway tracks (the distance between the rails) is 1.435 m.
Usage context:
Outside the US, heights, room sizes and short distances are all given in meters. It has been defined since 1983 as the distance light travels in a vacuum in 1/299,792,458 of a second.
Building drawings in metric countries are normally dimensioned in millimeters, with site plans and levels in meters. Surveyors work in meters too: the UTM map grid gives positions as eastings and northings in meters.
In science the meter is mostly used through its prefixes: visible light has a wavelength of 400 to 700 nanometers, and typical chemical bonds are 100 to 200 picometers long. At the other end, FM radio wavelengths are about 3 meters.