The
joule ( or ); symbol
J) is a
derived unit of
energy or
work in the
International System of Units. It is equal to the energy expended (or work done) in applying a
force of one
newton through a distance of one
metre (1 newton metre or N·m), or in passing an electric
current of one
ampere through a
resistance of one
ohm for one second. It is named after the English physicist
James Prescott Joule (1818–1889).
In terms of other SI units:
::
where N is Newton, m is metre, kg is kilogram, s is second, Pa is Pascal, and W is Watt.
One joule can also be defined as:
The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one '"coulomb volt" (C·V). This relationship can be used to define the volt.
The work required to produce one watt of power for one second, or one "watt second" (W·s) (compare kilowatt hour). This relationship can be used to define the watt.
Usage
Confusion with newton metre
It is dimensionally correct to say that 1 joule equals 1 newton metre (1 J = 1 N·m = 1 kg·m
2·s
−2); however, these units are
not interchangeable in practice. Instead, the
SI authority recommends using newton metres (N·m) as the unit of
torque, and joules as the unit of
energy. Since torque and energy are very different, this convention is useful to help avoid misunderstandings and miscommunications.
Multiples
:
For additional examples, see: Orders of magnitude (energy)
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Nanojoule
The nanojoule (nJ) is equal to one billionth of one joule. One nanojoule is about 1/160 of the
kinetic energy of a flying mosquito.
Microjoule
The microjoule (μJ) is equal to one millionth of one joule. The
Large Hadron Collider (LHC) is expected to produce collisions on the order of 1 microjoule (7
TeV) per particle.
Millijoule
The millijoule (mJ) is equal to one thousandth of one joule.
Kilojoule
The kilojoule (kJ) is equal to one thousand joules.
Food labels in some countries express
food energy in kilojoules. One kilojoule is about the maximum amount of
solar radiation received by one square metre of the
Earth in one second.
Megajoule
The megajoule (MJ) is equal to one million joules, or approximately the kinetic energy of a one-tonne vehicle moving at 160 km/h (100 mph).
Gigajoule
The gigajoule (GJ) is equal to one billion joules. Six gigajoules is about the amount of potential
chemical energy in a
barrel of oil, when combusted.
Terajoule
The terajoule (TJ) is equal to one trillion joules. About 60 terajoules were released by
the atomic bomb that exploded over Hiroshima.
Zettajoule
The zettajoule (ZJ) is equal to 10
21 joules.
Annual global energy consumption is approximately 0.5 ZJ
Conversions
1 joule is equal to:
(exactly)
(
electronvolts)
(thermochemical gram
calories or small calories)
(thermochemical kilocalories, kilogram calories, large calories or food calories)
(
British thermal unit)
(
foot-pounds force)
(foot-
poundals)
(exactly)
Units defined exactly 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 = (or 3.6 MJ)
1 ton TNT = 4.184 GJ
See also
Conversion of units
Orders of magnitude (energy)
Fluence
References
External links
Unit conversion from joule
Category:SI derived units
Category:Units of energy