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Why is the unit joule is written as "joule" and "J", I mean what does "J" mean and what does "joule" mean.

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closed as off-topic by Jan, ringo, Todd Minehardt, getafix, Klaus-Dieter Warzecha Nov 6 '16 at 22:54

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    $\begingroup$ I'm voting to close this question as off-topic because this is easily answerable by just about any research. $\endgroup$ – Jan Nov 6 '16 at 20:36
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In SI, every base units and many derived units have an official name and an official symbol. For example "meter"-"m", "second"-"s" or "joule"-"J".

There are grammatical rules how to use them, but more or less they are interchangeable. If you wonder about the capitalization: in English, the unit names are common nouns and not capitalized ("joule") even if they are derived from a person's name (Joule) or the symbol is a capital letter ("J").

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The joule , symbol "$\mathrm{J}$", is a derived unit of energy, work, or amount of heat in the SI Units. It is equal to the energy expended (or work done) in applying a force of one newton through a distance of one metre (1 newton metre or $\mathrm{N\cdot m}$), 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).

In terms firstly of base SI units and then in terms of other SI units:

$$\mathrm J = {}\rm \frac{kg \cdot m^2}{s^2} = N \cdot m = \rm Pa \cdot m^3={}\rm W \cdot s = C \cdot V$$

where $\mathrm{kg}$ is the kilogram, $\mathrm{m}$ is the metre, $\mathrm{s}$ is the second, $\mathrm{N}$ is the newton, $\mathrm{Pa}$ is the pascal, $\mathrm{W}$ is the watt, $\mathrm{C}$ is the coulomb, and $\mathrm{V}$ is the volt.

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" ($\mathrm{C\cdot V}$). 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" ($\mathrm{W\cdot s}$) (compare kilowatt hour). This relationship can be used to define the watt.

Source: Wikipedia.

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