Joule | |
---|---|
Unit system | SI derived unit |
Unit of | Energy |
Symbol | J |
Named after | James Prescott Joule |
1 J in ... | ... is equal to ... |
SI base units | kg⋅m2⋅s−2 |
CGS units | ×107 1erg |
kilowatt hours | ×10−7 kW⋅h 2.78 |
kilocalories (thermochemical) | ×10−4 kcalth 2.390 |
BTUs | ×10−4 BTU 9.48 |
electronvolts | ×1018 eV 6.24 |
|
The joule (/ˈdʒuːl/), symbol J, is a derived unit of energy in the International System of Units. 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 its 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).
In terms firstly of base SI units and then in terms of other SI units:
where kg is the kilogram, m is the metre, s is the second, N is the newton, Pa is the pascal, W is the watt, C is the coulomb, and V is the volt.
One joule can also be defined as:
This SI unit is named after James Prescott Joule. As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (J). However, when an SI unit is spelled out in English, it should always begin with a lower case letter (joule)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.— Based on The International System of Units, section 5.2.