Cubic ton
Encyclopedia
A Cubic ton is a measure of volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

 (compare fluid ounce
Fluid ounce
A fluid ounce is a unit of volume equal to about 28.4 mL in the imperial system or about 29.6 mL in the US system. The fluid ounce is distinct from the ounce, which measures mass...

).
It is no longer used in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 but seems to be still in use in the USA, see "definitions" below.

Definitions

A mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

-derived unit of volume must be defined by reference to the density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 of some material. In the case of the fluid ounce, this is water. For the cubic ton, the situation is more complex—there are different cubic tons for different materials.

The Reader's Digest Great Encyclopaedic Dictionary gives the following ton-derived volumes:
  • Timber, 40 cubic feet
    Cubic foot
    The cubic foot is an Imperial and US customary unit of volume, used in the United States and the United Kingdom. It is defined as the volume of a cube with sides of one foot in length.-Conversions:- Symbols :...

  • Stone, 16 cubic feet
  • Salt, 42 bushel
    Bushel
    A bushel is an imperial and U.S. customary unit of dry volume, equivalent in each of these systems to 4 pecks or 8 gallons. It is used for volumes of dry commodities , most often in agriculture...

    s
  • Lime, 40 bushels
  • Coke, 28 bushels
  • Wheat, 20 bushels


Defining a cubic ton presents some difficulties because:
  • It is uncertain whether the above figures are based on the long ton
    Long ton
    Long 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 tonne, and in the United States by the short ton...

     or the short ton
    Short ton
    The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...

  • Organic materials, such as timber, vary in density


The nearest thing to a standard
Standardization
Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....

 cubic ton seems to be the "timber" cubic ton (40 cubic feet) which is used by freight transport
Transport
Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...

 operators in the USA, ref:
http://www.saia.com/Glossary/default.asp#C and
http://www.nationalaircargo.com/tools/glossary.asp?SearchStart=C

Conversions

  • 1 cubic ton (40 cubic feet) = 1.133 cubic metre
    Cubic metre
    The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...

    s
  • 1 cubic metre = 0.883 cubic tons (35.32 cubic feet)


These are approximate
Approximation
An approximation is a representation of something that is not exact, but still close enough to be useful. Although approximation is most often applied to numbers, it is also frequently applied to such things as mathematical functions, shapes, and physical laws.Approximations may be used because...

 conversions, based on a cubic ton of 40 cubic feet, and will be subject to rounding errors
Round-off error
A round-off error, also called rounding error, is the difference between the calculated approximation of a number and its exact mathematical value. Numerical analysis specifically tries to estimate this error when using approximation equations and/or algorithms, especially when using finitely many...

.

Cubic tonne

There are many entries on the internet for cubic tonne but it is an unofficial unit. Its use should be discouraged because it is not an SI unit
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 and there is uncertainty about its definition. The SI does not use mass-derived units of volume and the SI unit of volume is the cubic metre
Cubic metre
The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...

.

The metric system
Metric system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

 formerly did use a mass-derived unit of volume, the litre
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...

, which was defined as the volume occupied by one kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

 of water. That definition is no longer used and the litre is now defined as one cubic decimetre, although traditionally both synonyms are recognized.

In view of this precedent it is possible that some metric countries may, in the past, have used a cubic tonne but it has never been officially used in the United Kingdom. No definition of the cubic tonne has been found but, if it were defined as the volume occupied by one tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

 of water, then it would be almost identical to the cubic metre.

Use by the BBC

The British Broadcasting Corporation (BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

) has used the term cubic tonne on at least three occasions:
  • In a television report on greenhouse gas
    Greenhouse gas
    A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

    es
  • In a television report on Silbury Hill
    Silbury Hill
    Silbury Hill is a prehistoric artificial chalk mound near Avebury in the English county of Wiltshire. It is part of the Stonehenge, Avebury and Associated Sites UNESCO World Heritage Site, and lies at ....

  • In an internet article on an Alpine
    Alps
    The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

    tunnel


The BBC's use of this unofficial unit caused some amusement in chatrooms, for example:
http://reddit.com/info/1bryu/comments
The BBC obviously realised its mistake because it later amended the internet article by changing cubic tonnes to cubic metres,
http://news.bbc.co.uk/1/hi/world/europe/6471241.stm
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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