# Joule

The joule (symbol J, also called newton meter, watt second, or coulomb volt) is the SI unit of energy and work. The unit is pronounced to rhyme with "tool", and is named in honor of the physicist James Prescott Joule (1818-1889).

1 joule = 1 N · 1 m = 1 newton · 1 metre = 1 kg · 1 m2 · 1 s−2
1 joule = 1 C · 1 V = 1 coulomb · 1 volt
1 joule = 1 W · 1 s = 1 watt · 1 second

One joule is the work done to exert a force of one newton for a distance of one metre, so the same quantity may be referred to as a newton metre or newton-metre (also with meter spelling), symbol N·m or N m. However, to avoid confusion the newton metre is usually used as a measure of torque, not energy.

Another way of visualizing the joule is the work required to lift a mass of about 102 g (e.g. a small apple) for one metre under the earth's gravity.

One joule is also the work required to move an electric charge of 1 coulomb through an electrical potential difference of 1 volt.

One joule is also the work done to produce power of one watt for one second, such as when somebody takes one second to lift the small apple mentioned above through one metre under the earth's gravity.

1 joule is equal to:

### Kilojoule

A kilojoule (abbreviation: kJ) is a unit of energy equal to 1000 joules.

• One kJ is the amount of work done by a one kilowatt device in one second.
• One kJ is sufficient to melt 3 grams of ice at 0 °C
• Approximately one kJ of work is done when 100 kilograms is lifted through one meter at Earth's surface (or, if one kilogram is lifted through 100 meters.)
• One kJ is equal to 5/18 (approx. 0.2778) of a watt hour.

### Megajoule

A megajoule (abbreviation: MJ) is a unit of energy equal to 1000000 joules.

• One MJ is the approximate amount of work done by a one kilowatt device in fifteen minutes.
• One MJ is sufficient to melt 3 kilograms of ice at 0 °C
• One MJ is equal to 5/18 (approx. 0.2778) of a kilowatt hour.
• One MJ is the approximate nutritional value of a half-liter of orange juice.

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