Joule
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Spiffy sperry
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{{for|the physicist named James Prescott Joule|James Prescott Joule}}
The '''joule''' (written in lower case, {{pronEng|ˈdʒuːl}} or {{IPA|/ˈdʒaʊl/}}) (symbol: '''J''') is the [[SI unit]] of [[energy]] measuring [[Joule heating|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 [[metre]] 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:
:<math>\, 1\, \mathrm{J}=1\, \mathrm{N} \cdot \mathrm{m}</math>
<br>
:<math>\, 1\, \mathrm{J}=1\, \mathrm{kg} \cdot \frac{\mathrm{m}^{2}}{\mathrm{s}^{2}}</math>
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
* The kinetic energy of a 2 kg mass moving at a velocity of 1 m/sec. The energy is linear in the mass but quadratic in the velocity, being given by ''E'' = ½''mv''².
* The potential energy of a 1 kg mass at an elevation of 1 m above a reference point in a gravitational field of 1 m/s². Earth's gravity being 9.81 m/s² at sea level, 1 kg at 1 m above the Earth's surface has a potential energy of 9.8 joules relative to that surface. When dropped the potential energy gradually becomes kinetic energy, with the conversion being complete at the instant the mass passes the reference point. Whereas kinetic energy is relative to an inertial frame, in this case that of the earth, potential energy is relative to a position, in this case the Earth's surface.
== Conversions ==
{{main|Conversion of units#Energy}}
1 joule is exactly 10<sup>7</sup> [[erg]]s.
1 joule is approximately equal to:
* 6.2415 {{e|18}} eV ([[electronvolt]]s)
* 0.2390 cal ([[calorie]]) (small calories, lower case c)
* 2.3901 {{e|−4}} kilocalorie, Calories (food energy, upper case C)
* 9.4782 {{e|−4}} BTU ([[British thermal unit]])
* 0.7376 ft·lbf ([[foot-pound force]])
* 23.7 ft·pdl (foot [[poundal]]s)
* 2.7778 {{e|−7}} [[kilowatt hour]]
* 2.7778 {{e|−4}} watt hour
* 9.8692 {{e|−3}} litre-[[atmosphere (unit)|atmosphere]]
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 {{e|6}} J (or 3.6 MJ)
* 1 ton TNT = 4.184 GJ
Useful to remember:
* 1 joule = 1 newton metre = 1 watt second
=== Practical examples ===
One joule in everyday life is approximately:
* the energy required to lift a small apple one [[metre]] 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 [[Earth's atmosphere|air]] by 1 degree Celsius.
* one hundredth of the energy a person can receive by drinking a single drop of [[beer]].
* the kinetic energy of an adult human moving a distance of about a handspan every second.
=== SI multiples ===<!-- This section is linked from [[Geothermal power]] -->
{{SI multiples
|unit=joule
|symbol=J
|note=Common multiples are in bold face
|m=|k=|mc=|M=|n=|G=|p=|T=
}}
{{SI unit lowercase|James Prescott Joule|joule|J}}
== See also ==
* [[Conversion of units]]
* [[SI prefix]]es
* [[Orders of magnitude]]
* [[Orders of magnitude (energy)]]
* [[Electronvolt]]
* [[Kilowatt hour]]
* [[Fluence]]
* [[Foe (unit of energy)|Foe]]
== References ==
<references />
* [http://www.fao.org/docrep/meeting/009/ae906e/ae906e17.htm 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 [[calorie]]s to joules in nutrition.
== External links ==
* [http://formularium.org/?go=122 Unit conversion from joule]
* [http://www.imperialtometric.com/conversion_en.htm Online Joule Converter]
* [http://www.worsleyschool.net/science/files/emc2/emc2.html Joule in E=mc²]
[[Category:SI derived units]]
[[Category:Units of energy]]
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