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" (pronounced in a North American accent), and is named in honor of the physicist James Prescott Joule (1818-1889).

1 joule = the work done in applying a force of one newton for a distance of one metre = 1 N · 1 m = 1 newton metre = 1 kg·m²·s⁻²

1 joule = the work required to move an electric charge of one coulomb through an electrical potential difference of one volt = 1 C · 1 V = 1 coulomb volt

1 joule = the work done to produce power of one watt continuously for one second = 1 W · 1 s = 1 watt second (compare kilowatt-hour)

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.

1 joule is equal to:

c. 2.78 × 10⁻⁷ kW·h (kilowatt hour)
c. 0.239 cal (calorie)
c. 0.000 948 BTU (British thermal unit)
c. 0.738 ft·lbf (foot pound force)
1 W·s (watt second)
1 N·m (newton metre)
c. 23.7 ft·pdl (foot poundals)
10 000 000 erg (ergs)

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 food energy of a half-liter of orange juice.
One MJ is the approximate food energy of 3 Bananas
One MJ is the approximate energy output of a 100 Bhp motor running for 15 seconds

Kilojoule

Megajoule

See also