Glossary · Vật lý
Joule
The SI unit of work and energy, symbol J. One joule equals one newton times one metre (N·m): the work done by a force of 1 newton moving an object 1 metre in the direction of the force.
The unit of work is a unit of force times a unit of length, in SI newtons times metres; that combination is called a joule. Kinetic energy has units of mass times speed squared, kg·m²/s², which is also the joule — because work and kinetic energy are forms of the same, more general physical property.
At the two ends of the scale, other units are common: the explosive yield of TNT and nuclear explosions is expressed in megatons, 1 megaton ≈ 4.18 × 10¹⁵ J; at the other extreme, the energy of subatomic particles is expressed in electron-volts, 1 eV ≈ 1.6 × 10⁻¹⁹ J.