What is a Joule? Definition and Uses of the Unit of Energy

A joule (J) is a unit of energy. It is defined as the energy expended when a force of one newton acts over a distance of one meter. It is named after James Prescott Joule, an English physicist who first measured the relationship between mechanical work and heat transfer in the mid-19th century.
The joule is commonly used to express the energy of various physical phenomena, such as the energy of motion (kinetic energy), the energy of position (potential energy), the energy of heat, and the energy of electromagnetic radiation. It is also used to describe the power output of machines and other devices that convert energy from one form to another.
One joule is a relatively small unit of energy, so it is often used in conjunction with other units, such as kilojoules (kJ) or megajoules (MJ), to express larger amounts of energy. For example, a car engine might produce 100 horsepower, which is equivalent to about 73,529 joules per minute.