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Joule

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The joule (or /ˈdʒaʊl/) (symbol: J) is the SI unit of energy measuring heat, electricity and mechanical work. It was named after English physicist James Prescott Joule.

Description

One joule is the work done, or energy expended, by a force of one newton moving one meter along the direction of the force. This quantity is also denoted as a newton metre with the symbol N·m. Note that torque also has the same units as work, but the quantities are not the same. In elementary units:
, 1, mathrm{J}=1, mathrm{N} cdot mathrm{m}

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

One joule is also:

  • 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

History

A joule is the mechanical equivalent of heat meaning the number of units of work in which the unit of heat can perform. Its value was found by James Prescott Joule in experiments that showed the mechanical energy Joule's equivalent, and represented by the symbol J. The term was first introduced by Dr. Mayer of Heilbronn.

Conversions

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 J (or 3.6 MJ)
  • 1 ton TNT = 4.184 GJ

Useful to remember:

  • 1 joule = 1 newton metre = 1 watt second

1 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 amount of energy, as heat, that a quiet person generates 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 get by drinking a single drop of beer.
  • the kinetic energy of an adult human moving 17 cm every second.

SI multiples

See also

References

External links



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Last updated on Wednesday March 12, 2008 at 15:45:54 PDT (GMT -0700)
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