Joule

Name	Joule
Standard	SI derived unit
Quantity	Energy
Symbol	J
Namedafter	James Prescott Joule
Units1	SI base units
Inunits1	1 kg·m2/s2
Units2	CGS units
Inunits2	erg
Units3	kilowatt hours
Inunits3
Units3	kilocalories
Inunits3

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 firstly of base SI units and then in terms of other SI units: :$\backslash rm\; J\; =\; \{\}\backslash rm\; \backslash frac\{kg\; \backslash cdot\; m^2\}\{s^2\}\; =\; N\; \backslash cdot\; m\; =\; \backslash rm\; Pa\; \backslash cdot\; m^3=\{\}\backslash rm\; W\; \backslash cdot\; s$

where N is the newton, m is the metre, kg is the kilogram, s is the second, Pa is the pascal, and W is the 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·m²·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.

the kinetic energy of a 50 kg human moving very slowly (0.2 m/s).

the kinetic energy of a tennis ball moving at 23 km/h (14 mph).

Multiples

:For additional examples, see: Orders of magnitude (energy) {|class=infobox |- | |}

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 (10³) joules. Food labels in some countries express food energy in kilojoules.

One kilojoule per second (1000 watts) is approximately the amount of solar radiation received by one square metre of the Earth in full daylight.

Megajoule

The megajoule (MJ) is equal to one million (10⁶) 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 (10⁹) 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 (10¹²) joules. About 63 terajoules were released by the atomic bomb that exploded over Hiroshima. The International Space Station, at completion, with a mass of 450,000kg and orbital velocity of 7.7 km/s, will have a kinetic energy of roughly 13 terajoules.

Petajoule

The petajoule (PJ) is equal to 10¹⁵ joules.

Exajoule

The exajoule (EJ) is equal to 10¹⁸ joules. The 2011 Tōhoku earthquake and tsunami in Japan had 1.41 EJ of energy according to its 9.0 on the Richter magnitude scale. Energy in the United States used per year is roughly 94 EJ.

Zettajoule

The zettajoule (ZJ) is equal to 10²¹ joules. Annual global energy consumption is approximately 0.5 ZJ

Yottajoule

The yottajoule (YJ) is equal to 10²⁴ joules. This is approximately the amount of energy required to heat the entire volume of water on Earth by 1˚Celsius.

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) (mass-energy equivalence) (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 of energy

Orders of magnitude (energy)

Fluence

References

External links

Unit conversion from joule

Category:SI derived units Category:Units of energy