Meter (m)
The meter is the base unit of length in the International System of Units (SI) and the foundation of the metric system. Spelled "metre" in British English, it is used by virtually every country on Earth for science, engineering, construction, and daily life. One meter is roughly the distance from the floor to a door handle, or about 3.28 feet.
Definition
Since 1983, one meter is defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second. This definition links the meter directly to the physical constant for the speed of light (299,792,458 m/s). All other metric length units derive from the meter: one kilometer equals 1,000 meters, one centimeter equals 0.01 meters, and one millimeter equals 0.001 meters.
History
The meter was conceived during the French Revolution as a universal, nature-based unit of length. In 1791, the French Academy of Sciences defined it as one ten-millionth of the distance from the North Pole to the equator along the meridian through Paris. A platinum bar embodying this length was cast in 1799 and served as the standard for nearly a century. In 1889, a more precise platinum-iridium prototype replaced it. By 1960, the definition shifted to wavelengths of krypton-86 light, and in 1983 the meter received its current definition: the distance light travels in a vacuum in exactly 1/299,792,458 of a second. This ties the meter to the speed of light, making it one of the most precisely defined units in science.
Common Uses
The meter is the default unit for measuring room dimensions, building heights, athletic tracks, swimming pools, and fabric lengths in most of the world. Road signs in metric countries show distances in kilometers (thousands of meters). Scientists use meters and its sub-multiples (millimeters, micrometers, nanometers) for everything from measuring cell sizes to specifying laser wavelengths. In the United States, meters appear in scientific and military contexts, while feet and yards dominate everyday use.
Did You Know? Facts About Meter
- The original 1799 platinum meter bar is still preserved at the National Archives in Paris.
- Light travels one meter in about 3.3 nanoseconds - roughly the time it takes a modern CPU to execute one clock cycle.
- The meter was once defined by a physical object, making it the last SI base unit to be redefined in terms of a fundamental constant.
- A guitar is typically about one meter long, making it a handy everyday reference.
- Only three countries - the United States, Liberia, and Myanmar - have not officially adopted the metric system, though all three use the meter in scientific contexts.