Tonne

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This article is about the metric tonne. For the imperial ton, see Ton.

A tonne (t) or metric ton (M/T), sometimes referred to as a metric tonne, is a measurement of mass equal to 1,000 kilograms. It is not an SI unit but is accepted for use with the SI.[1] The proper SI unit for a tonne would be a "megagram", but this term is never used in practice. Though the spelling tonne predates the introduction of the SI system in 1960, it is now used as the standard spelling for the metric mass measurement in English. The similar Imperial units and United States customary units are spelled ton in English.

This unit was defined in the United States in 1866[2] as a millier or a tonneau. However, neither of these are in use and though they still appear in the statute, they have been declared obsolete by NIST.[3]

Contents

[edit] Definition

1 tonne is defined as 1000 kilograms or 1 megagram.

[edit] Multiples

Multiple Name Symbol Multiple Name Symbol
100 tonne t      
101 decatonne dat 10–1 decitonne dt
102 hectotonne ht 10–2 centitonne ct
103 kilotonne kt 10–3 millitonne mt
106 megatonne Mt 10–6 microtonne µt
109 gigatonne Gt 10–9 nanotonne nt
1012 teratonne Tt 10–12 picotonne pt
1015 petatonne Pt 10–15 femtotonne ft
1018 exatonne Et 10–18 attotonne at
1021 zettatonne Zt 10–21 zeptotonne zt
1024 yottatonne Yt 10–24 yoctotonne yt

[edit] Origin

The spelling tonne is from French. In Old English the spelling was tunne. The various spellings and meanings (tonne, ton, tun) derive from the late Latin tunna, "cask" - a full cask about a metre high could easily weigh a tonne. It may also be of Celtic origin.

[edit] Conversions

One tonne is equivalent to:

  • 1000/0.45359237 pounds (exactly by definition), giving 2204.622 621 848 775 807 ... pounds (to 12 significant digits)
       the easy to remember 2204.622 622 (to six significant digits)
       or roughly 2205 pounds (good enough for most calculations since loading (worst case) is usually the concern of interest)

  • and by comparison the imperial measurements long ton and short ton are exactly 2240 and 2000 pounds, respectively.
    In percentages (inverted): the tonne is 98.44% (101.605%) that of a long ton, and 110.25% (90.72%) that of a short ton,

  • 1.000 000 megagram (exactly). Symbol Mg. This is the official SI term, but not generally used colloquially, nor in industry and shipping.

[edit] Explanation

The official symbol is t. T and mT and mt (especially in the combination mmt for "million metric tons" compare to Mt for megatonne) are also sometimes used, but all of these are deprecated since they conflict with internationally agreed SI symbols. T is the SI symbol for the tesla and m is SI prefix 'milli', meaning 1000th (though in practice fractional prefixes aren't generally used with the tonne).

In France and the English-speaking countries that are predominantly metric, the spelling tonne is widespread. However, in Britain, the ton used prior to metrication was the long ton of 2240 pounds (approximately 1016 kg). This is so close to the tonne that many people draw little distinction and continue to use the old spelling. For example, even the Guinness Book of World Records accepts metrication without marking this by changing the spelling. For the United States, metric ton is the name for this unit used and recommended by NIST. [3] In the U.S. an unqualified mention of a "ton" almost invariably refers to a short ton of 2000 lb (about 907 kg).

Like grams and kilograms, tonnes gave rise to a (now obsolete) force unit of the same name: 1 tonne-force = 9.80665 kilonewtons (kN), a unit also often called simply "tonne" or "metric ton" without identifying it as a unit of force. Note that it is only the tonne as a unit of mass which is accepted for use with SI; the tonne-force or metric ton-force is not acceptable for use with SI.

[edit] Use of mass as proxy for energy

Main article: Tonne of TNT

The tonne of trinitrotoluene (TNT) is used as a proxy for energy. Prefixes are also used e.g. kilotonne, megatonne, gigatonne; especially for expressing nuclear weapon yield, based on a specific combustion energy of TNT of 4.184 MJ/kg (or one calorie—specifically a thermochemical calorie—per milligram). Hence, 1 kt TNT = 4.184 TJ, 1 Mt TNT = 4.184 PJ.

The SI unit of energy is the joule. Assuming that TNT contains 1000 small (thermochemical) calories per gram (4.184 kJ/g), one tonne TNT is more correctly referred to as 4.184 gigajoules. It is usually used to describe the energy of explosions.

[edit] Metric ton in popular culture


[edit] Derived Units

  • metric ton unit

A metric ton unit (mtu) traditionally referred to one metric ton(ne) of ore containing 1% of the desired metal, though in our day usage it is practically just a measure for certain metals (especially in price quotes), thus it is a unit of mass equaling 10kg or one hundredth of a tonne.

http://www.emis.platts.com/thezone/guides/platts/metals/conversion.html

http://www.unc.edu/~rowlett/units/dictM.html


[edit] See also

[edit] References

  1. ^ Section 4.1 of The International System of Units (SI), 8th Edition, 2006
  2. ^ Act of July 28, 1866, codified in 15 U.S.C. §205 [1]
  3. ^ "Metric System of Measurement: Interpretation of the International System of Units for the United States", Federal Register notice of July 28, 1998, 63 F.R. 40333 [2]

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