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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;
Conversions
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1 joule is exactly 107 ergs.
1 joule is approximately equal to:
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 |
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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.
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See also
References
External links
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