joule
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(jūl, joul) 
n. (Abbr. J or j)
n. (Abbr. J or j)
- The International System unit of electrical, mechanical, and thermal energy.
- A unit of electrical energy equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second.
- A unit of energy equal to the work done when a force of one newton acts through a distance of one meter.
[After James Prescott JOULE.]
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[Etymology: J. P. Joule; UK 1818-89] energy, work, quantity of heat. Symbol J. The joules of work done by a steady current equal the product of the number of coulombs of charge and the electromotive force in volts. J = C·V.
SI, Metric-m.k.s. A. Also = N·m (= m2·kg·s-2 in base terms). The following are among the coherent derived units:
• J·m-3 for energy density;
• J·kg-1 for specific energy;
• J·kg-1 = gray for absorbed radiation;
• J·kg-1 = sievert for dose equivalent;
• J·s-1 = watt for power, radiant flux;
• J·K-1 for entropy, heat capacity;
• J·mol-1 for molar energy;
• J·mol-1·K-1 for molar entropy or molar heat capacity;
• J·V-1 = coulomb for quantity of electricity;
• J·C-1 = volt for electromotive force, potential difference;
• J·kg-1·K-1 for specific entropy or specific heat capacity.
See also practical unit.
History
The joule was recognized internationally in 1889, at the second International Electrical Conference, as a derived addition to the practical units of the c.g.s. system; it was defined as the energy dissipated in 1 second by current of 1 ampere flowing through a resistance of 1 ohm. Hence the practical joule. While discrepancies, for the underlying ampere and ohm, between measured absolute values (in centimetre-gram-second terms) and their laboratory specifications led the IEC in 1908 to rename units based on the latter as unadorned international units, differing by 0.05~ % from the practical, the joule as a mechanical unit was unequivocally a force of 107 dyne acting over 1 centimetre (= 107 erg).
With the implementation of the m.k.s.A. system in 1948, this became 1 newton acting over 1 metre (leaving its electric definition unchanged). The same year, the joule was accepted as a unit of heat; prior to this, and despite the initial electric definition of 1889 using the expression ‘the energy disengaged as heat in one second’, the joule was regarded as a mechanical equivalent of, but not a measure of heat.
| 1946 | CIPM ‘Joule (unit of work or energy) The joule is the work done when the point of application of 1 MKS unit of force [newton] moves a distance of 1 metre in the direction of the force.’see note below |
[Le Système International d'Unités (Sèvres, France: Bureau International de Poids et Mesures, 1985)]
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A unit of energy in the MKS system. It is equal to 10,000,000 ergs in the CGS system. Surge protectors are often given joule ratings, but this refers only to the amount of energy they can absorb, not what gets through. See CGS system.
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Unit of energy; approximately 4.2 joules (J) equal one calorie. One kilojoule (kJ) equals 1000 J and is the amount of heat required to raise the temperature of 239 g of water by 1°C; and 1 megajoule (MJ) equals 1000 kJ.
A unit of energy or work; equals the work done by a force of 1 newton which acts over a distance of 1 metre in the direction of the force.
Columbia Encyclopedia:
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joule
joule (jūl, joul), abbr. J, unit of work or energy in the mks system of units, which is based on the metric system; it is the work done or energy expended by a force of 1 newton acting through a distance of 1 meter. The joule is named for James P. Joule.
Unit Conversions:
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joules
To convert from joules to:
Btu,
multiply by 9.48E-04.
ergs,
multiply by 10000000.
foot-pounds,
multiply by .7376.
kg-calories,
multiply by .0002389.
kg-meters,
multiply by .102.
watt-hrs,
multiply by .0002778.
poundals,
multiply by 723.3.
pounds,
multiply by 22.48.
Related measurements:
joules/cm
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joule
IN BRIEF: n. - A unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second.
Tutor's tip: A "jewel" is a (precious stone), a "joule" is (a measure of energy in physics). Do not confuse these with "jowl" which refers to (the jaw and the loose skin of the throat).
LearnThatWord.com is a free vocabulary and spelling program where you only pay for results!
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symbol: J; the SI derived unit of energy, work, or heat, equal to a force of one newton acting over a distance of one metre; i.e. 1 J = 1 N m = 1 W s. The joule is equivalent to 107 ergs and is the energy dissipated by one watt in one second. [After James Prescott Joule (1818 — 89), British physicist.]
| joining peptide, joining gene, joinase | |
| jumonji, jumping gene, juvenile hormone |
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categories related to 'joule'
- Principles of Mechanics, Waves, and Measurement - joule: SI unit of work or energy equal to one newton acting through one meter
- Tools, Tests, Units, and Scales - joule: SI unit of energy, equal to the force of one newton acting through one meter, or 107 ergs
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This article is about the unit of energy. For other uses, see Joule (disambiguation).
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| Unit system: | SI derived unit |
| Unit of... | Energy |
| Symbol: | J |
| Named after: | James Prescott Joule |
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| 1 J in... | is equal to... |
| SI base units | 1 kg·m2/s2 |
| CGS units | 1×107 erg |
| kilowatt hours | 2.78×10−7 kW·h |
| kilocalories | 2.39×10−4 kcal |
| BTUs | 9.48×10−4 BTU |
| electronvolts | 6.24×1018 eV |
The joule (
/ˈdʒuːl/ or sometimes /ˈdʒaʊl/); 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 meter (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).[1][2][3]
In terms firstly of base SI units and then in terms of other SI units:
where N is the newton, m is the meter, 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.
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Contents
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Usage
This SI unit is named after James Prescott Joule. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (J). When an SI unit is spelled out in English, it should always begin with a lower case 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.
Confusion with newton metre
Main article: newton metre
Although the joule has the same dimensions as the newton-metre (1 J = 1 N·m = 1 kg·m2·s−2), these units are not interchangeable as the newton-metre (N·m) is the unit of torque and joules the unit of energy.[4] Torque and energy are related to each other using the equation
- where E is the energy, τ is magnitude of the torque, and θ is the angle moved (in radians). Since radians are dimensionless, it follows that torque and energy have the same dimensions.
The use of newton-metres for torque and joules for energy is useful in helping avoid misunderstandings and miscommunications.[4]
Torque and energy have the same dimension because both torque and work (a type of energy) can be calculated by multiplying a force by a distance. However, the details are quite different in the two cases. For torque, the multiplication of force and distance is a vector cross product, while for work it is a dot product. Also, for torque, the distance involved is the length of the lever arm, while for energy it is the distance traveled by the object undergoing the force.
Practical examples
One joule in everyday life is approximately:
- the energy required to lift a small apple one metre straight up. (A mass of about 102 g = 1⁄9.81 kg)
- the energy released when that same apple falls one metre to the ground.
- the energy released as heat by a person at rest, every 1/60th of a second.[5]
- 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).[6]
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.[7]
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. Outside of North America, nutrition facts labels are markedly different from those in the United States; in particular, energy is usually expressed in standard kilojoules (kJ) rather than Calories.
One kilojoule per second (1000 watts) is approximately the amount of solar radiation received by one square metre of the Earth in full daylight.[8]
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).
Because 1 watt times one second equals one joule, 1 kilowatt-hour is 1000 watts times 3600 seconds, or 3.6 megajoules.
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.[9]
Terajoule
The terajoule (TJ) is equal to one trillion (1012) joules. About 63 terajoules were released by the atomic bomb that exploded over Hiroshima.[10] The International Space Station, at completion, with a mass of 450,000kg and orbital velocity of 7.7 km/s,[11] will have a kinetic energy of roughly 13 terajoules.
Petajoule
The petajoule (PJ) is equal to 1015 joules. 210 PJ is equivalent to about 50 megatons of TNT. This is the amount of energy released by the Tsar Bomba, the largest man-made nuclear explosion ever.
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 moment 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
Main article: Conversion of units of energy
1 joule is equal to:
- 1×107 ergs (exactly)
- 6.24150974×1018 eV (electronvolts)
- 0.2390 cal (thermochemical gram calories or small calories)
- 2.3901×10−4 kcal (thermochemical kilocalories, kilogram calories, large calories or food calories)
- 9.4782×10−4 BTU (British thermal unit)
- 0.7376 ft·lbf (foot-pounds 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
- 11.1265 femtograms (mass-energy equivalence)
- 1×10−44 foe (exactly)
Units defined exactly in terms of the joule include:
- 1 thermochemical calorie = 4.184 J[12]
- 1 International Table calorie = 4.1868 J[12]
- 1 watt hour = 3600 J
- 1 kilowatt hour = 3.6×106 J (or 3.6 MJ)
- 1 watt second = 1 J
- 1 ton TNT = 4.184 GJ
See also
References
- ^ American Heritage Dictionary of the English Language, Online Edition (2009). Houghton Mifflin Co., hosted by Yahoo! Education.
- ^ The American Heritage Dictionary, Second College Edition (1985). Boston: Houghton Mifflin Co., p. 691.
- ^ McGraw-Hill Dictionary of Physics, Fifth Edition (1997). McGraw-Hill, Inc., p. 224.
- ^ a b From the official SI website: "A derived unit can often be expressed in different ways by combining base units with derived units having special names. Joule, for example, may formally be written newton metre, or kilogram metre squared per second squared. This, however, is an algebraic freedom to be governed by common sense physical considerations; in a given situation some forms may be more helpful than others. In practice, with certain quantities, preference is given to the use of certain special unit names, or combinations of unit names, to facilitate the distinction between different quantities having the same dimension."
- ^ This is called the basal metabolic rate. It corresponds to about 1200 kilocalories (also called dietary calories) per day. "At rest" means awake but inactive.
- ^ Ristinen, Robert A.; Kraushaar, Jack J. (2006). Energy and the Environment (2nd ed.). Hoboken, NJ: John Wiley & Sons. ISBN 0-471-73989-8.
- ^ CERN - Glossary
- ^ "Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to present". http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant. Retrieved 2005-10-05.
- ^ IRS publication
- ^ Los Alamos National Laboratory report LA-8819, The yields of the Hiroshima and Nagasaki nuclear explosions by John Malik, September 1985. Available online at http://www.mbe.doe.gov/me70/manhattan/publications/LANLHiroshimaNagasakiYields.pdf
- ^ International Space Station Fact Sheet
- ^ a b 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
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Joule
Dansk (Danish)
n. - joule, kalorie, wattsekund
Ελληνική (Greek)
n. - (φυσ.) (μονάδα) τζάουλ
Italiano (Italian)
joule (unità di energia)
Português (Portuguese)
n. - joule (m) (medida de energia) (Fís.)
Español (Spanish)
n. - julio, joule
中文（简体）(Chinese (Simplified))
焦耳
中文（繁體）(Chinese (Traditional))
n. - 焦耳
العربيه (Arabic)
(الاسم) جول ( وحدة طاقه كهربائيه)
עברית (Hebrew)
n. - ג'אול (יחידת אנרגיה/עבודה)
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