Kilometre

Division of the meridien

Kilometre (American spelling: kilometer, symbol: km) is a unit of length in the metric system, equal to one thousand metres, the International System of Units (SI) base unit of length. It is now the most widely used unit of measurement for expressing distances between geographical locations on land in most of the world.

History

The kilometre was first introduced in 1795 as part of the French metric system in France. This system was designed to simplify and unify measurements by basing them on the decimal system. The metre was defined as one ten-millionth of the distance from the North Pole to the Equator through Paris. From this definition, the kilometre was derived as being equal to 1,000 metres.

Usage

The kilometre is used worldwide as a measure of distance in road signs, maps, and for official purposes in almost all countries, with notable exceptions being the United States and the United Kingdom, where the mile is still used for some purposes. In athletics, the kilometre is used in track and field events, road races, and for cross country distances.

Conversion

One kilometre is equivalent to:

• 0.621371 miles
• 1,093.61 yards
• 3,280.84 feet

Conversely:

• 1 mile = 1.60934 kilometres
• 1 yard = 0.0009144 kilometres
• 1 foot = 0.0003048 kilometres

Scientific Significance

In science and engineering, the kilometre is used in various fields such as astronomy, where distances between celestial objects are often expressed in kilometres. In geography, it is used to measure distances between locations on the Earth's surface. The kilometre is also used in the measurement of wavelengths of infrared radiation, where the micrometre (one millionth of a metre) is often preferred.

Cultural Aspects

The use of the kilometre varies by country and culture, with some countries adopting the kilometre for all purposes, while others use it alongside traditional units. The adoption of the kilometre is often seen as a move towards metrication, the process of converting to the metric system.

See Also

• Metric system
• International System of Units
• Length measurement
• Conversion of units

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