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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. [11]
Energy is defined via work, so the SI unit of energy is the same as the unit of work – the joule (J), named in honour of James Prescott Joule [1] and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units
A newton is defined as 1 kg⋅m/s 2 (it is a named derived unit defined in terms of the SI base units). [1]: 137 One newton is, therefore, the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force.
The electronvolt is divided by the Boltzmann constant to convert to the Kelvin scale: / = = , where k B is the Boltzmann constant. The k B is assumed when using the electronvolt to express temperature, for example, a typical magnetic confinement fusion plasma is 15 keV (kiloelectronvolt), which is equal to 174 MK (megakelvin).
Symbol [1] Name of quantity Unit name Symbol Base units E energy: joule: J = C⋅V = W⋅s kg⋅m 2 ⋅s −2: Q electric charge: coulomb: C A⋅s I electric current: ampere
joule (SI unit) J The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force. [32] = 1 J = 1 m⋅N = 1 kg⋅m 2 /s 2 = 1 C⋅V = 1 W⋅s kilocalorie; large calorie: kcal; Cal ≡ 1000 cal IT = 4.1868 × 10 3 J: kilowatt-hour; Board of Trade Unit: kW⋅h; B.O.T.U. ≡ 1 kW × 1 h
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.
In physics, natural unit systems are measurement systems for which selected physical constants have been set to 1 through nondimensionalization of physical units.For example, the speed of light c may be set to 1, and it may then be omitted, equating mass and energy directly E = m rather than using c as a conversion factor in the typical mass–energy equivalence equation E = mc 2.