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The joule (symbol: J) is the SI unit of energy, or work. It is named in honor of the physicist James Prescott Joule (1818–1889).
DefinitionEdit
The joule is a derived unit defined as the work done, or energy required, to exert a force of one newton for a distance of one meter, so the same quantity may be referred to as a newton meter or newton-meter (also with metre spelling), with the symbol N·m or N m. It can also be written as kg·m^{2}·s^{−2}. However, the newton meter is usually used as a measure of torque, not energy.
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
ConversionsEdit
1 joule is exactly 10^{7} erg.
1 joule is approximately equal to:
- 6.241506363 × 10^{18} eV (electron-volts)
- 0.239 cal (calorie) (small calories)
- 2.390 × 10^{-4} Calorie or kilocalorie (food)
- 9.48 × 10^{-4} BTU (British thermal unit)
- 0.738 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
- the energy required to lift a small apple (102 g) one meter against Earth's gravity
Units defined in terms of the joule include:
- 1 thermochemical calorie = 4.184 J (exact)
- 1 International Table calorie = 4.1868 J (exact)
- 1 watt-hour = 3600 J (exact)