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Units of measurement

Summary

Five tables are used to convert the main units of the metric system: length, mass, capacity, area, volume.

The exercise mode displays random conversion operations of measurement, to solve using the table. Each step can be validated and corrected.

 

Learning objectives

  • To know the units of measure.
  • To know how to compare and convert units of measure.
  • To introduce the history of the International System of Units.

Learn more

Units of measurement have always been part of everyday language, they regulate trade and science. Originally, populations had their own units of measurement, usually based on body parts (finger, foot, thumb, forearm, foot, armspan, height of current king, etc.). This diversity made it impossible to compare measurements between them. Any conversion was difficult.

With the development of industry, commerce and science, it was urgent to reform the system of measures. In the 18th century, a universal reference was defined with the metre.

The metre becomes the first base unit corresponding to the ten-millionth of the quarter the length of the meridian. Then, with advances in metrology, the metre is defined (in 1983) as the length that light travels in a vacuum for a period of 1/299 792 458 second (light travels at the speed of 299 792 458 m/s).

All other units are derived from the metre:

  • the kilogram is equal to the mass of water contained in a cube, one decimetre per side, at the temperature of 4 °C.
  • the litre is a measure of capacity whose capacity corresponds to that of a cube that measures one decimetre per side.
  • the square metre (m2) is the area of a square measuring one metre per side.
  • the cubic metre (m3) is the volume of a cube measuring one metre per side. 

 The metric system is a decimal system that relates each units multiples and submultiples by powers of 10. Each new unit is derived from the base unit by adding a prefix.

The metric system is completed by other measures of reference (the ampere for the electrical current intensity, kelvin for temperature, ...) creating the International System of Units (SI stands for "Système International" in french) adopted by the almost all countries.

The accuracy and preservation of measurement standards are assigned to the "Bureau International des Poids et Mesures" (BIPM), in Sèvres, France, established in 1875.

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