Joule

The done or energy required to exert a force of one newton for a distance of one metre, so the same quantity may be referred to as a newton metre or newton-metre with the symbol N&middot;m. However, the newton metre is usually used as a measure of work.

Definition
As a rough guide, 1 joule is the absolute minimum amount of energy required to lift a one kilogram object up by a height of 10 centimetres on the surface of the Earth.

Other definitions
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&middot;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&middot;s

Conversions
1 joule is exactly 107 ergs.

1 joule is approximately equal to:
 * 6.24150636309 eV (electron-volts)
 * 0.238845896628 cal (calorie) (small calories)
 * 2.390 kilocalorie (food)
 * 9.47817120313 BTU (British thermal unit)
 * 0.737562149277 ft&middot;lbf (foot-pound force)
 * 23.7 ft&middot;pdl (foot poundals)
 * 2.7778 kilowatt-hour
 * 2.7778 watt-hour
 * 9.8692 litre-atmosphere

Also, some very rough approximations of a joule from the real world are: Units defined in terms of the joule include:
 * the energy required to lift a small apple (102 g) one metre against Earth's gravity.
 * the amount of energy, as heat, that a quiet person produces every hundredth of a second.
 * the energy required to heat one gram of dry, cool air by 1 degree Celsius.
 * 1/100th of the energy a person can get by drinking a single droplet of beer.
 * 1 thermochemical calorie = 4.184 J (exact)
 * 1 International Table calorie = 4.1868 J (exact)
 * 1 watt-hour = 3600 J (exact)
 * 1 kWh = 1 kilowatt-hour = 3.6 J = 3.6 MJ

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.

Istography (References)

 * 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 calories to joules in nutrition.
 * Conversion of J in other units