Joule

For the physicist named James Prescott Joule, see James Prescott Joule.

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

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

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;

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.

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.

Joule

Contents

Conversions

Practical examples

SI multiples

See also

References

External links