For the physicist named James Prescott Joule, see James Prescott Joule.
For the electric car, see Optimal Energy Joule.

The joule is the derived unit of energy in the International System of Units. It is defined as:

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

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

  • The work done by a force of one newton traveling through a distance of one meter;
  • The work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt, with the symbol C·V;
  • The work done to produce power of one watt continuously for one second; or one watt second (compare kilowatt hour), with the symbol W·s. Thus a kilowatt hour is 3,600,000 joules or 3.6 megajoules;
  • The kinetic energy of a 2 kg mass moving at a velocity of 1 m/s. The energy is linear in the mass but quadratic in the velocity, being given by E = ½mv²;

Contents

Conversions

Main article: Conversion of units#Energy

1 joule is exactly 107 ergs.

1 joule is approximately equal to:

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 exploding = 4.184 GJ

Useful to remember:

  • 1 joule = 1 newton meter = 1 watt 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 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.

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.

See also

References

External links

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

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