# Joule

• joule
unit systemsi derived unit
unit ofenergy
symbolj
named afterjames prescott joule
conversions
1 j in ...... is equal to ...
si base units   kgm2s−2
cgs units   1×107 erg
kilowatt hours   2.78×10−7 kw⋅h
kilocalories (thermochemical)   2.390×10−4 kcalth
btus   9.48×10−4 btu
electronvolts   6.24×1018 ev

the joule (l/ jawl, jool;[1][2][3] symbol: j) is a derived unit of energy in the international system of units.[4] it is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one metre (1 newton metre or n⋅m). 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).[5][6][7]

in terms firstly of base si units and then in terms of other si units, a joule is defined below (please consider this table for the meaning of symbols):

symbol meaning
kg kilogram
m metre
s second
n newton
pa pascal
w watt
c coulomb
v volt

one joule can also be defined as the following:

• 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 – 3.6 megajoules). this relationship can be used to define the watt.

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
• practical examples
• multiples
• conversions
• newton metre and torque
• watt-second