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The joule (symbol J) is the SI unit of energy—a measure of the capacity to do work or generate heat. One joule equals the work done (or energy expended) by a force of one newton (N) acting over a distance of one meter (m). One newton equals a force that produces an acceleration of one meter per second (s) per second on a one kilogram (kg) mass. Therefore, one joule equals one newton•meter. Expressed in equations: The mechanical quantities involved have the SI units: It follows that J (joule) is expressed in SI basic units as: .'Joule' is variously pronounced 'jool' (rhymes with 'jewel') or 'joul' (rhymes with 'jowl'). One may also use electric units to define the joule. One joule measures the energy released by a electric charge of one coulomb dropping one volt in absolute value of electrical potential. The amount of energy delivered by a one watt source of power in one second is one Joule. The joule is also used to measure thermal energy. One calorie of heat is the equivalent of 4.186 J. The joule is named for James Prescott Joule (1818 - 1889), who studied the relation between mechanical and heat energy discovered earlier by count Rumford. One joule represents a relatively small amount of energy; it takes roughly 100,000 J (105 J) to heat a cup of water from room temperature to its boiling point under standard conditions. Often, kilojoules (kJ) are used, kJ = 103 J. [edit] Other units of energy convertible to joulesWhereas the joule is the standard SI unit of energy, many other units of energy, all convertible to joules, are used in particular circumstances. Those include: erg; foot pound; watt second; watt hour; kilowatt hour; thermochemical calorie; International Table calorie; kilocalorie; thermochemical Btu; therm; quad; cubic meter natural gas; ton of oil equivalent; ton of coal equivalent; ton of TNT; electron volt; hartree; inverse meter; inverse second; kelvin; kilogram.[1] One kilogram (kg) of mass is equivalent to exactly 89,875,517,873,681,764 joules (according to E=mc2 with m = 1 kg and speed of light c = 299,792,458 m/s).[1] [edit] Practical examples
[edit] References cited
The joule ( JOOL, also non-standard JOWL;[1][2][3][4][5][disputed – discuss] symbol: J) is the unit of energy in the International System of Units (SI).[6] It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).[7][8][9] Definition[edit]In terms of SI base units and in terms of SI derived units with special names, the joule is defined as
One joule can also be defined by any of the following:
The joule is named after James Prescott Joule. As with every SI unit named for a person, its symbol starts with an upper case letter (J), but when written in full it follows the rules for capitalisation of a common noun; i.e., "joule" becomes capitalised at the beginning of a sentence and in titles, but is otherwise in lower case. History[edit]The cgs system had been declared official in 1881, at the first International Electrical Congress. The erg was adopted as its unit of energy in 1882. Wilhelm Siemens, in his inauguration speech as chairman of the British Association for the Advancement of Science (23 August 1882) first proposed the Joule as unit of heat, to be derived from the electromagnetic units Ampere and Ohm, in cgs units equivalent to 107 erg. The naming of the unit in honour of James Prescott Joule (1818–1889), at the time retired but still living (aged 63), is due to Siemens: "Such a heat unit, if found acceptable, might with great propriety, I think, be called the Joule, after the man who has done so much to develop the dynamical theory of heat."[10]At the second International Electrical Congress, on 31 August 1889, the joule was officially adopted alongside the watt and the quadrant (later renamed to henry).[11] Joule died in the same year, on 11 October 1889. At the fourth congress (1893), the "international ampere" and "international ohm" were defined, with slight changes in the specifications for their measurement, with the "international joule" being the unit derived from them.[12] In 1935, the International Electrotechnical Commission (as the successor organisation of the International Electrical Congress) adopted the "Giorgi system", which by virtue of assuming a defined value for the magnetic constant also implied a redefinition of the Joule. The Giorgi system was approved by the International Committee for Weights and Measures in 1946. The joule was now no longer defined based on electromagnetic unit, but instead as the unit of work performed by one unit of force (at the time not yet named newton) over the distance of 1 metre. The joule was explicitly intended as the unit of energy to be used in both electromagnetic and mechanical contexts.[13] The ratification of the definition at the ninth General Conference on Weights and Measures, in 1948, added the specification that the joule was also to be preferred as the unit of heat in the context of calorimetry, thereby officially deprecating the use of the calorie.[14] This definition was the direct precursor of the joule as adopted in the modern International System of Units in 1960. The definition of the joule as J = kg⋅m2⋅s−2 has remained unchanged since 1946, but the joule as a derived unit has inherited changes in the definitions of the second (in 1960 and 1967), the metre (in 1983) and the kilogram (in 2019). Practical examples[edit]One joule represents (approximately):
Multiples[edit]SI multiples of joule (J)
Conversions[edit]1 joule is equal to (approximately unless otherwise stated):
Units defined exactly in terms of the joule include:
Newton-metre and torque[edit]In mechanics, the concept of force (in some direction) has a close analogue in the concept of torque (about some angle):
A result of this similarity is that the SI unit for torque is the newton-metre, which works out algebraically to have the same dimensions as the joule, but they are not interchangeable. The General Conference on Weights and Measures has given the unit of energy the name joule, but has not given the unit of torque any special name, hence it is simply the newton-metre (N⋅m) – a compound name derived from its constituent parts.[30] The use of newton-metres for torque and joules for energy is helpful to avoid misunderstandings and miscommunications.[30] The distinction may be seen also in the fact that energy is a scalar quantity – the dot product of a force vector and a displacement vector. By contrast, torque is a vector – the cross product of a force vector and a distance vector. Torque and energy are related to one another by the equation where E is energy, τ is (the vector magnitude of) torque, and θ is the angle swept (in radians). Since plane angles are dimensionless, it follows that torque and energy have the same dimensions. Watt-second[edit]A watt-second (symbol W s or W⋅s) is a derived unit of energy equivalent to the joule.[31] The watt-second is the energy equivalent to the power of one watt sustained for one second. While the watt-second is equivalent to the joule in both units and meaning, there are some contexts in which the term "watt-second" is used instead of "joule", such as in the rating of photographic electronic flash units. [32] See also[edit]
Notes[edit]
References[edit]
External links[edit]
What is the unit equivalent to joule?1 Joule [J] = 1 Watt-second [Ws] = 1 V A s = 1 N m = 1 kg m2s−2.
What is the 1 joule value?joule, unit of work or energy in the International System of Units (SI); it is equal to the work done by a force of one newton acting through one metre. Named in honour of the English physicist James Prescott Joule, it equals 107 ergs, or approximately 0.7377 foot-pounds.
What is another form of 1 joule?A watt-second (symbol W s or W⋅s) is a derived unit of energy equivalent to the joule.
What is an example of 1 joule?In physics, it's common to talk about joules of energy — one example used to illustrate a joule is lifting an apple, which weighs about one Newton. If you raise the apple one meter in the air, you've used one joule of work.
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