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Tonne

A tonne (t) or metric ton (U.S.), also referred to as a metric tonne, is a measurement of mass equal to 1,000 kg or 2,204.62262 lb, or approximately the mass of one cubic metre of water. It is not an SI unit but is accepted for use with the SI. If prefixes were used completely consistently, the SI unit for a tonne would be a megagram, or Mg (see SI prefix), but this term is rarely used. The spelling tonne pre-dates the introduction of the SI system in 1960 (it has been used in France for about two and a half centuries),[citation needed] and is now used as the standard spelling for the metric mass measurement in most English-speaking countries. In the U.S., the units were originally referred to using the French words millier or tonneau, but these terms are now obsolete. The Imperial and US customary units comparable to the tonne are both spelled ton in English.

Origin
The spelling tonne is from Gallic and French. The term applied to the barrel of the largest size. In Old English the spelling was tunne, "cask" - a full cask about a metre high could easily weigh a tonne. The antiquated British wine cask volume measurement tun is close to a metric tonne in weight as it defines about 954 litres which for many commonly used liquids (aqueous solutions) approximates to as many kilograms.

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 occasionally 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 0.001.) Te is also sometimes used, particularly in the nuclear industry.

In France and the English-speaking countries that are predominantly metric, the spelling tonne is widespread. This is generally true in Britain, however, the ton used prior to metrication was the long ton of 2,240 pounds (1,020 kg) (approximately) and this is so close to the tonne that some 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.[4] In the U.S. an unqualified mention of a "ton" almost invariably refers to a short ton of 2,000 pounds (907.1847 kg).

Like the gram and the kilogram, the tonne gave rise to a (now obsolete) force unit of the same name, the tonne-force, equivalent to about 9.8 kilonewtons: 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, as the SI unit of force is the Newton.

Long ton

Long ton, (weight ton, or imperial ton) is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used in the United Kingdom and several other Commonwealth countries. It has been mostly replaced by the short ton in the United States and the tonne (metric ton) elsewhere. It is equal to 2,240 pounds (1,016.0469088 kg) or 35 cubic feet (0.99108963 m3) of salt water with a density of 1.025 g/ml[1]. It has some limited use in the United States, most commonly in measuring the displacement of ships, and was the unit prescribed for warships (e.g. battleships limited to 35,000 long tons (35,561.6 t)) in the international agreements between the world wars.

Sulfur as recovered in an oil refinery is a product that is commonly measured in long tons.

The standard ton in the U.S. measurement system is the "short ton", equal to 2,000 pounds (907.18474 kg) (exactly). Both long and short tons are defined as 20 hundredweights, but a hundredweight is 112 pounds (50.8 kg) (which is equal to 8 stone, 1 stone/6.35 kilograms) in the Imperial system (long or gross hundredweight) and 100 pounds (45.4 kg) in the U.S. system (short or net hundredweight).

The spelling "tonne" denotes the metric tonne of 1,000 kg (2,204.623 lb) (approximately).

A long ton-force is 2,240 pounds-force (9,964.0164182 N)

Short ton

The short ton (S/T) is a unit of weight equal to 2,000 pounds (907.18474 kg) [1]. In the United States it is often called simply ton[1] without distinguishing it from the metric ton (or tonne, 1,000 kilograms) or the long ton (2,240 pounds (1,020 kg)); rather, the other two are specifically noted. There are, however, some U.S. applications for which unspecified tons normally means long tons (for example, Navy ships)[2] or metric tons (world grain production figures).

Both the long and short ton are defined as 20 hundredweights[1], but a hundredweight is 112 pounds (50.8 kg) (which is equal to 8 stone, 1 stone/6.35 kilograms) in the Imperial system (long or gross hundredweight)[1] and 100 pounds (45.4 kg) in the U.S. system (short or net hundredweight)[1].

The spelling tonne is from Gallic and French. The term applied to the barrel of the largest size. In Old English the spelling was tunne, "cask". A full cask about a metre high could easily weigh a metric tonne, since the volume of the antiquated British wine cask tun is defined as 954 litres which for water (density = 1 g/cm3) amounts to as many kilograms. In the context of heraldry, the term 'tun' is also recognized -- again meaning a very large barrel, such as a brewer might use. For example, tuns are part of the blazon of the brewer's guild of London, England.[citation needed]

A short ton–force is 2,000 pounds-force (8,896.4432 N).

　吨 <量>
　　(形声。从口,屯声。本义:重量单位。公制1吨为 1000 公斤)
　　同本义
　　质量和重量的单位
　　等于 20 长担或 2240磅的单位,主要用于英国――亦称“长吨”(long ton)
　　等于20短担或2000磅的单位,主要用于美国、加拿大和南非――亦称“短吨”(short ton)
　　船舶的内部容积单位,等于100立方英尺――亦称“注册吨” (register ton)

    1长吨=1.01605公吨=1016.046KG=2240磅=1.12短吨

     1吨=1000千克
　　1长担=50.802千克
　　1短担=45.4千克
　　1长吨=200长担=1016.0千克
　　1短吨=200短担=907.2千克

　　中国是按照公吨，长吨、短吨是英美国家的计量单位。
　　用来计算船只排水,约等于一长吨海水体积的单位,用来计算船舶排水量,亦等于35立方英尺――亦称“排水吨”(displacement ton)
　　船舶装载容积的单位, 通
　　吨 dūn
　　①重量单位。1吨为1000千克（合2000市斤）。
　　②指'登记吨'，计算船只容积的单位，1登记吨等于2.83立方米。
　　【吨位】
　　①车、船等规定的最大载重量。船舶的吨位为满载排水量与空船排水量之差。
　　②计算船舶载重量时按船的容积计算，以登记吨为一吨位。