Wikipedia:Joule
From Global Warming Art
The joule (symbol J), named for James Prescott Joule, is the derived unit of energy in the International System of Units. It is the energy exerted by a force of one newton acting to move an object through a distance of one metre. In terms of dimensions:
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Definition
One joule is defined as the amount of work done by a force of one newton moving an object through a distance of one metre. Other relationships are:
- The work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt (C·V). (This relationship can be used to define the volt);
- The work required to continuously produce one watt of power for one second; or one watt second (W·s) (compare kilowatt hour). (This relationship can be used to define the watt)
Conversions
1 joule is equal to:
- 1×107 ergs (exactly)
- 6.24150974×1018 eV (electronvolts)
- 0.2390 cal (thermochemical gram calories or small calories)
- 2.3901×10−4 kcal (thermochemical kilocalories, kilogram calories, large calories or food calories)
- 9.4782×10−4 BTU (British thermal unit)
- 0.7376 ft·lbf (foot-pound force)
- 23.7 ft·pdl (foot-poundals)
- 2.7778×10−7 kilowatt-hour
- 2.7778×10−4 watt-hour
- 9.8692×10−3 litre-atmosphere
- 1×10−44 Foe (exactly)
Units defined in terms of the joule include:
- 1 thermochemical calorie = 4.184 J
- 1 International Table calorie = 4.1868 J
- 1 watt hour = 3600 J
- 1 kilowatt hour = 3.6×106 J (or 3.6 MJ)
- 1 ton TNT = 4.184 GJ
Useful to remember:
- 1 joule = 1 newton × 1 metre = 1 watt × 1 second
Practical examples
One joule in everyday life is approximately:
- the energy required to lift a small apple one meter straight up.
- the energy released when that same apple falls one meter to the ground.
- the energy released as heat by a person at rest, every hundredth of a second.
- the energy required to heat one gram of dry, cool air by 1 degree Celsius.
- one hundredth of the energy a person can receive by drinking a drop of beer.
- the kinetic energy of an adult human moving at a speed of about a handspan every second.
SI multiples
| Submultiples | Multiples | |||||
|---|---|---|---|---|---|---|
| Value | Symbol | Name | Value | Symbol | Name | |
| 10–1 J | dJ | decijoule | 101 J | daJ | decajoule | |
| 10–2 J | cJ | centijoule | 102 J | hJ | hectojoule | |
| 10–3 J | mJ | millijoule | 103 J | kJ | kilojoule | |
| 10–6 J | µJ | microjoule | 106 J | MJ | megajoule | |
| 10–9 J | nJ | nanojoule | 109 J | GJ | gigajoule | |
| 10–12 J | pJ | picojoule | 1012 J | TJ | terajoule | |
| 10–15 J | fJ | femtojoule | 1015 J | PJ | petajoule | |
| 10–18 J | aJ | attojoule | 1018 J | EJ | exajoule | |
| 10–21 J | zJ | zeptojoule | 1021 J | ZJ | zettajoule | |
| 10–24 J | yJ | yoctojoule | 1024 J | YJ | yottajoule | |
| Common multiples are in bold face | ||||||
This SI unit is named after James Prescott Joule. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is uppercase (J). When an SI unit is spelled out in English, it should always begin with a lowercase letter (joule), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.
—Based on The International System of Units, section 5.2.
See also
References
- The adoption of joules as units of energy, FAO/WHO Ad Hoc Committee of Experts on Energy and Protein, 1971. A report on the changeover from calories to joules in nutrition.
