The relationship between them is:1km =1000 m.

Male:

I. Overview:

"meter", the basic unit of length in the international system of units, with the symbol M, can be used to measure length, width and height.

The definition of "meter" originated in France. The length of 1 meter was originally defined as one ten thousandth of the distance from the equator of the earth to the north pole on the meridian passing through Paris, and then the international meter origin was determined. With the deepening of people's understanding of measurement, the definition of the length of meter has been revised several times.

Definition: From 1983, the length of the meter is defined as "the distance traveled by light in vacuum 1/299792458 seconds".

Second, the development process:

(a), put forward

1688, British philosopher and priest John Wilkins put forward the necessity of decimal standard length unit system.

1675, the Italian scientist Ti Tuo Livio Bratini first used the word metro cattolico in his paper, which originated from the Greek μ? τρον καθολικ? ν (métron katholikón), which means "universal unit of measurement".

1789 After the victory of the French Revolution, the National Assembly ordered the French Academy of Sciences to organize a committee, the unified measurement System. The Committee put forward a new metric system and suggested that one tenth of the distance from the equator to the North Pole on the meridian passing through Paris (that is, one fortieth of the meridian of the earth) be used as the standard unit. They called this unit mètre, which later evolved into meter, and the Chinese translation is "Mi Tu" or "meter". 179 1 year, which was approved by the French parliament. [4-7]17991210 France adopted the metric system and began to formally use it.

(2) Definition of Meridian

Although the irregular surface of the earth is not a perfect sphere, France still uses this measurement result to determine the length of the standard meter. Later, it was found that the length of the first archived meter was less than that defined by meridian 1/5 mm, because the oblateness of the earth and the arc length were miscalculated. But this length is still the standard. So in the end, the circumference of the earth passing through the pole is a little more than 40 million meters (40007863 meters).

1875 On May 20th, the French government came forward, held a meeting of representatives of 20 governments, and formally signed the Metric Convention, recognizing the metric system as an international unit of measurement. At the same time, it was decided to establish the International Metrology Committee and the International Bureau of Metrology. As of June 1985 and June 10, the metric convention has 47 members. Participation of China 1977.

(3), rice original device

1889 international rice primitive device

1792- 1799, led by French astronomers, made a survey of the sky from Dunkirk, France to Barcelona, Spain. 1799, according to the measurement results, a short-section platinum rod of 3.5 mm× 25 mm was made, and the distance between the two ends of the rod was set as 1 m, which was kept by the French archives, so it was also called "archival meter". This is the earliest definition of rice, and this primitive rice utensil has been kept in the Paris Archives.

1889, No.6 rice prototype (3 1 temporary platinum-iridium alloy rice prototype (90% platinum and 10% iridium) is closest to the length of archival rice at 0℃) was selected as the international rice prototype at the first international metrology conference (CGPM). It is stipulated that when the ambient air temperature is 0℃, the distance between the two ends of the rice cooker is 1m. 1927. The definition of rice was strictly stipulated in the Seventh International Metrology Conference. In addition to the temperature requirement, it is also proposed that the raw rice container should be kept at the standard atmospheric pressure 1, and its placement method is specified in detail.

But in fact, due to the scribing technology, material deformation, measurement methods and other reasons, the length given by the original meter is not necessarily exactly 1m, and there is always a certain error when reproducing the value, which is about 0. 1μm (0. 1μ m). In addition, if the original rice cooker is damaged, there will be no basis for copying, especially it is difficult to ensure that the replica is completely consistent with the original rice cooker, which brings difficulties to the use of various countries.

(4), spectrum definition

At the end of 19, scientists discovered the red spectral line of natural cadmium (Cd) in the experiment, which has very good clarity and reproducibility. In dry air at 15℃, its wavelength is equal to y = 6438.4696×10-10 meter. According to the international agreement 1927, it was decided to use this spectral line as the length standard of spectroscopy, and1m =155164438+03y CD was determined. People found the intangible standard that can be used to define the meter for the first time.

Scientists continued their research, and later found that the orange spectral line of krypton (86Kr) was better than the red spectral line of cadmium. 1960, at the1/CGPM, it was decided to replace the red line of cadmium with the orange line of krypton (86Kr), and the definition of rice was changed to: "The length of rice is equal to 2P 10 and 5d/kl of krypton -86 atoms in vacuum. This natural benchmark has stable performance, no deformation problem, easy replication and high replication accuracy. The relative error is not more than 4× 10-9, which is equivalent to not less than 4 microns in the length measurement of 1 km.

After the 1960s, due to the appearance of laser, people discovered a superior light source. Using laser instead of krypton spectrum can make the length measurement more accurate. As long as a certain time interval is determined, the unit of length can be defined from the product of the speed of light and this time interval.

(v) Final definition

In the 1970s, the measurement of the speed of light was very accurate. In 1983, the International Conference on Weights and Measures (CGPM) redefined the definition of rice. "The distance that light travels in vacuum is 1/299 792 458 seconds" as the standard meter.

Third, the unit conversion:

Meters of units at all levels

Note: the meter is also called "meter", the kilometer is also called "kilometer", the decimeter is also called "square inch", the centimeter is also called "centimeter", the millimeter is also called "millimeter" and the femto meter is also called "Fermi".