Information about Joules

The joule (IPA: [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, electricity and mechanical work.

Description

One joule is the work done, or energy expended, by a force of one newton moving an object one metre along the direction of the force. This quantity is also denoted as a Newton-meter with the symbol N·m. Note that torque also has the same units as work, but the quantities are not identical. In elementary units:

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.

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.

Conversions

Main article: Conversion of units#Energy, work, or heat

1 joule is exactly 10⁷ ergs.

1 joule is approximately equal to:

• 6.24150636309 10¹⁸ eV (electronvolts)
• 0.238845896628 cal (calorie) (small calories, lower case c)
• 2.390 10⁻⁴ kilocalorie, Calories (food energy, upper case C)
• 9.47817120313 10⁻⁴ BTU (British thermal unit)
• 0.737562149277 ft·lb_f (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)

Useful to remember:

• 1 joule = 1 newton-meter = 1 watt-second

1 joule in everyday life 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 hundredth of the energy a person can get by drinking a single 5 mm diameter droplet of beer.

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	J
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

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.

See also

• Conversion of units
• SI prefixes
• Orders of magnitude
• Orders of magnitude (energy)
• Electronvolt
• Watt-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