What Is the SI Unit of Work?


Scientists and engineers have a variety of units they use to describe the amount of work performed by a chemical reaction, a machine or an electric current. The units science uses to measure work are the same as the units used to measure the energy required to do the work. In the SI system of measurement, more commonly known as the metric system, there is a specific unit allocated to both work and energy.

Definition of Work

  • Science defines work a bit differently than the common everyday understanding of the term. In science, work is produced when a force moves over a distance. By this definition, someone performs work by pushing a block several feet, but not by pushing against an unmoving brick wall. Mathematically, the work is measured by the product of the force used, in metric units of newtons, and the distance covered, in metric units of meters.

SI Unit

  • The SI unit for work is the same as the unit for energy, the joule. The joule is known as a "derived" unit, meaning it is formed from a mathematical operation on other "base" metric units. Specifically, the joule is defined as a force of one newton moving through a distance of one meter, or a Newton-meter (N-m). The Newton is also a derived unit and is equal to a kilogram-meter per second squared (kg-m/s^2), which makes the joule equal to a kilogram-meter squared per second squared (kg-m^2/s^2).

Prefixes and Abbreviations

  • The metric system uses a standard set of prefixes to the base units, which give the magnitude of the measurement. These also apply to joules. For example, the prefix "kilo" means one thousand, so a kilojoule would be one thousand joules. In keeping with metric policy, you don't capitalize the word joule if you are writing it out in full, but you do use a capital J when you abbreviate it. Kilo is not capitalized in its abbreviation, so kilojoule would be abbreviated as kJ.

More About Joules

  • The unit of the joule was named in honor of the famous scientist James Prescott Joule, who conducted a great deal of important research into aspects of heat energy. Scientists use joules in a variety of ways. One example is that the work done by gravity when a mass falls a distance is the acceleration of gravity (9.8 m/s^2) multiplied by the mass in kg and the distance in m. The metric system also uses joules to measure energy and so the work done by gravity is equal to the kinetic energy gained by the falling mass.


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