Joule
The joule is the unit of energy in the International System of Units. In terms of SI base units, one joule corresponds to one kilogram-metre squared per second squared One joule is equal to the amount of work done when a force of one newton displaces a body through a distance of one metre in the direction of that force. 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.
Definition
According to the International Bureau of Weights and Measures the joule is defined as "the work done when the point of application of 1 MKS unit of force moves a distance of 1 metre in the direction of the force."In terms of SI base units and in terms of SI derived units with special names, the joule is defined as
One joule is also equivalent to any of the following:
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 first proposed the joule as unit of heat, to be derived from the electromagnetic units ampere and ohm, in cgs units equivalent to. The naming of the unit in honour of James Prescott Joule, at the time retired and aged 63, followed the recommendation of Siemens: At the second International Electrical Congress, on 31 August 1889, the joule was officially adopted alongside the watt and the quadrant. Joule died in the same year, on 11 October 1889. At the fourth congress, 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. In 1935, the International Electrotechnical Commission 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 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. 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. This is the definition declared 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, the metre and the kilogram. Practical examplesOne joule represents :
; : is about the kinetic energy of a flying mosquito. ; : The Large Hadron Collider produces collisions of the microjoule order per particle. ; : Nutritional food labels in most countries express energy in kilojoules. One square metre of the Earth receives about of solar radiation every second in full daylight. A human in a sprint has approximately 3 kJ of kinetic energy, while a cheetah in a sprint has approximately 20 kJ.. ; : The megajoule is approximately the kinetic energy of a one megagram vehicle moving at . The energy required to heat of liquid water at constant pressure from to is approximately.. ; : is about the chemical energy of combusting of petroleum. 2 GJ is about the Planck energy unit. . ; : The terajoule is about . About of energy was released by Little Boy. The International Space Station, with a mass of approximately and orbital velocity of, has a kinetic energy of roughly. In 2017, Hurricane Irma was estimated to have a peak wind energy of. . ; : is about of TNT, which is the amount of energy released by the Tsar Bomba, the largest man-made explosion ever.. ; : The 2011 Tōhoku earthquake and tsunami in Japan had of energy according to its rating of 9.0 on the moment magnitude scale. Yearly U.S. energy consumption amounts to roughly, and the world final energy consumption was in 2021. One petawatt-hour of electricity, or any other form of energy, is. ; : The zettajoule is somewhat more than the amount of energy required to heat the Baltic Sea by 1 °C, assuming properties similar to those of pure water. Human annual world energy consumption is approximately. The energy to raise the temperature of Earth's atmosphere 1 °C is approximately. ; : The yottajoule is a little less than the amount of energy required to heat the Indian Ocean by 1 °C, assuming properties similar to those of pure water. The thermal output of the Sun is approximately per second. Conversions1 joule is equal to :
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 – a compound name derived from its constituent parts. The use of newton-metres for torque but joules for energy is helpful to avoid misunderstandings and miscommunication. 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 torque, and θ is the angle swept. Since plane angles are dimensionless, it follows that torque and energy have the same dimensions. Watt-secondA watt-second is a derived unit of energy equivalent to the joule. 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. |