Joule

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This article is about the unit of energy. For other uses, see Joule (disambiguation).

The joule (symbol J) 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. Algebraically:

\, 1\, \mathrm{J}=1\, \mathrm{kg} \cdot \mathrm{m}^{2} \cdot \mathrm{s}^{-2}

Contents

[edit] Definition

One joule is the amount of energy required to perform the following physical actions:

[edit] Conversions

Main article: Conversion of units#Energy

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

[edit] 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 quiet person, 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 a distance of about a handspan every second.

[edit] SI multiples

SI multiples for joule (J)
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.


[edit] See also

[edit] References

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Joule"
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