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The joule is the derived unit of energy in the International System of Units. It is defined as:

One joule is the amount of energy required to perform the following actions:

• The work done by a force of one newton travelling through a distance of one meter;
• 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/s. The energy is linear in the mass but quadratic in the velocity, being given by E = ½mv²;

Contents 1 Conversions 1.1 Practical examples 1.2 SI multiples 2 See also 3 References 4 External links

Conversions

Main article: Conversion of units#Energy

1 joule is exactly 10⁷ ergs.

1 joule is approximately equal to:

• 6.2415 ×10¹⁸ eV (electronvolts)
• 0.2390 cal (calorie) (small calories, lower case c)
• 2.3901 ×10⁻⁴ kilocalorie, Calories (food energy, upper case C)
• 9.4782 ×10⁻⁴ BTU (British thermal unit)
• 0.7376 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

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 ×10⁶ J (or 3.6 MJ)
• 1 ton TNT = 4.184 GJ

Useful to remember:

• 1 joule = 1 newton meter = 1 watt second

Practical examples

One 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 energy released as heat by a quiet person, 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 receive by drinking a drop of beer.
• the kinetic energy of an adult human moving a distance of about a handspan every second.

SI multiples

SI multiples for joule (J)

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

This SI unit is named after James Prescott Joule. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is uppercase (J). When an SI unit is spelled out in English, it should always begin with a lowercase letter (joule), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. — Based on The International System of Units, section 5.2.

See also

• Conversion of units
• SI prefixes
• Orders of magnitude
• Orders of magnitude (energy)
• Electronvolt
• Kilowatt hour
• Fluence
• Foe

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.

External links

• Unit conversion from joule
• Online Joule Converter
• Joule in E=mc²

Wikipedia content modification information:

• This page was last modified on 5 December 2008, at 07:12.

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