Joule

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The joule (IPA pronunciation: [dʒuːl] or [dʒaʊl]) (symbol: J) is the SI unit of energy. It was named after James Prescott Joule for his work on the relationship between heat and mechanical work.

1 Description
2 History
3 Conversions

[edit] Description

One joule is the work done, or energy expended, by a force of one newton moving an object one meter along the direction of the force. Thus, the same quantity may be referred to as a newton metre or newton-metre with the symbol N·m. However, since the newton metre usually refers to torque, which is a quite different measure, the joule is a less ambiguous unit. In elementary units:

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

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

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.

[edit] 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.

[edit] Conversions

1 joule is exactly 10⁷ ergs.

1 joule is approximately equal to:

6.24150636309 ×10¹⁸ eV (electron-volts)
0.238845896628 cal (calorie) (small calories, lowercase c)
2.390 ×10⁻⁴ kilocalorie, Calorie (food energy, uppercase C)
9.47817120313 ×10 ⁻⁴ BTU (British thermal unit)
0.737562149277 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

1 joule in the real world is approximately:

the energy required to lift a small apple (102 g) one meter 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.
one hundreth of the energy a person can get by drinking a single 5 mm diameter droplet of beer.

Units defined in terms of the joule include:

**Units of energy**
	Joule (SI unit)	thermochemical calorie	International Table calorie	watt-hour	kilowatt-hour (kWH)
1 Joule	≡ 1 J	≈	≈	≈	≈
1 thermochemical calorie	= 4.184 J	≡ 1 cal (thermo)	≈	≈	≈
1 International Table calorie	= 4.1868 J	≈	≡ 1 cal (IT)	≈	≈
1 watt-hour	= 3600 J	≈	≈	≡ 1 WH	≈
1 kilowatt-hour	= 3.6×10⁶ J	≈	≈	≡ 1×10³ WH	≡ 1 kWH

[edit] SI multiples

Multiple	Name	Symbol	Multiple	Name	Symbol
10⁰	joule	J
10¹	decajoule	daJ	10^–1	decijoule	dJ
10²	hectojoule	hJ	10^–2	centijoule	cJ
10³	kilojoule	kJ	10^–3	millijoule	mJ
10⁶	megajoule	MJ	10^–6	microjoule	µJ
10⁹	gigajoule	GJ	10^–9	nanojoule	nJ
10¹²	terajoule	TJ	10^–12	picojoule	pJ
10¹⁵	petajoule	PJ	10^–15	femtojoule	fJ
10¹⁸	exajoule	EJ	10^–18	attojoule	aJ
10²¹	zettajoule	ZJ	10^–21	zeptojoule	zJ
10²⁴	yottajoule	YJ	10^–24	yoctojoule	yJ

[edit] See also

This SI unit is named after James Prescott Joule. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (J). But when an SI unit is spelled out, it should always be written in lowercase (joule), unless it begins a sentence or is the name "degree Celsius".

— Based on The International System of Units, section 5.2.

[edit] 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.

Orders of magnitude (energy) SI unit: joule Conversion of units#Energy, work, or heat
1 E-30 J	1 E-24 J	1 E-18 J	1 E-12 J	1 E-6 J	1 J	1 E6 J	1 E12 J	1 E18 J	1 E24 J	1 E30 J
1 E-29 J	1 E-23 J	1 E-17 J	1 E-11 J	1 E-5 J	10 J	1 E7 J	1 E13 J	1 E19 J	1 E25 J	1 E33 J
1 E-28 J	1 E-22 J	1 E-16 J	1 E-10 J	1 E-4 J	100 J	1 E8 J	1 E14 J	1 E20 J	1 E26 J	1 E36 J
1 E-27 J	1 E-21 J	1 E-15 J	1 E-9 J	1 E-3 J	1000 J	1 E9 J	1 E15 J	1 E21 J	1 E27 J	1 E39 J
1 E-26 J	1 E-20 J	1 E-14 J	1 E-8 J	1 E-2 J	10000 J	1 E10 J	1 E16 J	1 E22 J	1 E28 J	1 E42 J
1 E-25 J	1 E-19 J	1 E-13 J	1 E-7 J	1 E-1 J	100,000 J	1 E11 J	1 E17 J	1 E23 J	1 E29 J	1 E45 J