The metric system is a system of measurement that is used around the world. It is based on decimals (units of ten). It developed from a system introduced by France in 1795. In 1960 the metric system was given a new name - the International System of Units (which is often written "SI" for short). This is the official system of measurement in almost every country in the world.
Description[change | edit source]
The names of most units of measure in the metric system have two parts. One part is the unit name and the other part is the prefix. For example, in the name "centimetre", the word "centi" is the prefix and the word "metre" is the unit name. Sometimes, as with metre, litre and gram, there is no prefix.
In the metric system, all units have a "symbol". Symbols are a shorthand way of writing the names of unuts. All the countries in the world use the same symbol for a unit, even though they might have different ways of writing out the unit name in full. For example
- People write "kilometre" in the United Kingdom
- People write "kilometer" in the United States
- People write "quilómetro" in Portugal
- People write "χιλιόμετρα" in Greece
- Everybody uses the symbol "km" for "kilometer".
Unit names[change | edit source]
- In the metric system, length is measured in metres. The symbol for the metre is the letter "m". The metre was originally defined as being 1⁄10,000,000 of the distance between the North Pole and the Equator on the meridian that passed through Paris. Between 1791 and 1799 the distance between Dunkirk and Barcelona was measured. The angle of certain stars above the horizon was also measured. Scientists used these measurements to calculate the size of the metre. In 1799, a platinum bar that was equal to this length was made. After that scientists could check that rulers and tape measures were correct.
- In the metric system, volume is measured in litres. The symbol for the litre is "L". In 1795 the French Government defined one litre must have the same volume as a cube which had sides that were 10 centimetres.
- In the metric system, weight[Note 1] is measured in grams. The symbol for the gram is the letter "g". In 1795 the French Government defined the gram as the weight of one cubic centimeter of water at the freezing point of ice. This was difficult to measure, so in 1799 the French Government made a "prototype kilogram" (1000 grams) weight that scientists could use to check their own weights.
- In the metric system, temperature is measured in degrees Celsius. The symbol for degrees Celsius is "°C".
Prefixes[change | edit source]
- The prefix milli is used to show that a measurement is 1⁄1000 (or 0.001) of the base measurement:
- There are 1000 milligrams (mg) is a gram.
- There are 1000 millimetres (mm) in a metre.
- There are 1000 millilitres (mL) in a litre.
- The prefix centi is used to show that a measurement is 1⁄100 (or 0.01) of the base measurement:
- There are 100 centimetres (cm) in a metre.
- There are 100 centilitres (cL) in a litre.
- The prefix kilo is used to show that a measurement is 1000 times as large of the base measurement:
- There are 1000 grams is a kilogram (kg).
- There are 1000 metres in a kilometre (km).
There are a lot of other prefixes. Some of them are:
- micro which means one millionth (1⁄1,000,000). The symbol for "micro" is a a Greek letter μ (called "mu").
- deci which means one tenth (1⁄10). The symbol for "deci" is "d".
- mega which means one million (1,000,000). The symbol for "mega" is "M". You must be careful not to get "m" (for "milli") and "M" (for "mega") mixed up.
How big[change | edit source]
These tables will help you to estimate the size of different lengths or weights in the metric system. In these tables:
- The symbol "~" means "about".
- The word "Imperial" is short for Imperial units which are the units of measure that have traditionally been used in the United Kingdom.
- The word "Customary" is short for U.S. customary units which are units of measure that have traditionally been used in the United States.
Length[change | edit source]
|1 km||0.621 miles
|The Mall (from Trafalgar Square to Buckingham Palace)
Niagara Falls (Bank to bank)
|100 m||109 yd||Length of a gridiron football, association football (soccer) or rugby field
Length of four-coach train
|10 m||33 ft||Width of a tennis court (10.97 m)|
|Length of a baseball bat (maximum = 1.067 m)
Length of a cricket bat (maximum = 0.965 m)
|10 cm||4 in||Width of a man's palm|
|2⁄5 in||Width of an average acorn|
|1 mm||0.04 in||Thickness of denim cloth|
|100 μm||0.004 in||Thickness of a piece of photo-copier paper|
Weight[change | edit source]
0.984 tons (UK)
1.102 tons (US)
|A small motor car - typically powered by an engine of between 1.0 and 1.2 L|
|100 kg||15 st 11 lbs (UK)
220.5 lbs (US)
|A large man - About 15% of US Caucasian males exceed 100 kg|
|10 kg||22.05 lbs||Average weight of a 12-month old child|
|1 kg||2.205 lbs||One litre drink (excluding the weight of the container)|
|100 g||33⁄4 oz||Midway between a tennis ball (~58 g) and a cricket ball (~160 g) or a baseball (~145 g)|
|10 g||2⁄5 oz||A large coin
|1 g||15.4 grains||Two peanut seeds|
Related pages[change | edit source]
Notes[change | edit source]
- In this article, the word "weight" is used instead of "mass"
References[change | edit source]
- "Decree on weights and measures". 7 April 1795. http://smdsi.quartier-rural.org/histoire/18germ_3.htm. "Gramme, le poids absolu d'un volume d'eau pure égal au cube de la centième partie du mètre , et à la température de la glace fondante." English translation: "Gramme: the absolute weight of a volume of pure water equal to the cube of the hundredth part of the meter, at the temperature of melting ice."
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), ISBN 92-822-2213-6, http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf
- Harmer, S.W.; Rezgui, N.; Bowring, N.; Luklinska, Z.; Ren, G.. "Determination of the Complex Permittivity of Textiles and Leather in the 14-40 GHz, mm wave band using a Free-W ave Transmittance Only Method". IET Microwaves, Antennas & Propagation: 8. https://uhra.herts.ac.uk/dspace/bitstream/2299/2418/1/902311.pdf. Retrieved 2011-10-08.
- Halls, Steven B.; Hanson, John (2008). "Men's Weight Chart". http://www.halls.md/chart/men-weight-w.htm. Retrieved 2011-09-17.
- Halls, Steven B.; Hanson, John (2008). "Child Growth Charts of height weight and body mass index". http://www.halls.md/chart/child-growth/pediatric.htm. Retrieved 2011-09-17.
- "€ - our money - Common sides". European Central Bank. 2011. http://www.ecb.int/euro/coins/common/html/index.en.html. Retrieved 2011-09-17.
- Wang, Ming; Pittman, Roy (6 August 2008). "Resveratrol Content in Seeds of Peanut Germplasm Quantified by HPLC". Plant Genetic Resources: Characterization and Utilization. (United States Department of Agriculture - Agricultural Research Service) 7 (1): 80–83. http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=230823. Retrieved 12 October 2011.