Joule

The joule is the SI derived unit of energy and work, equal to one newton metre or one kilogram metre squared per second squared.

Newton (unit): The SI derived unit of force, equal to one kilogram metre per second squared. A joule is the work done when a one-newton force moves an object one metre.
Work (physics): Energy transferred when a force causes displacement; for a constant force along the displacement, it is force times distance. One joule is the work done by one newton over one metre.
Calorie: A non-SI unit of energy, with definitions including the thermochemical calorie of exactly 4.184 joules. Food energy is commonly labeled in kilocalories rather than joules.
James Prescott Joule: The nineteenth-century English physicist whose experiments established the quantitative relationship between mechanical work and heat. The SI unit of energy was named in recognition of his work.
Conservation of energy: The physical principle that energy in an isolated system remains constant, though it can change form. Joules provide a common measure for tracking energy across transformations.
Metre: The SI base unit of length, defined by the distance light travels in vacuum in a specified fraction of a second. The joule equals a newton multiplied by a metre of displacement.
Kinetic energy: The energy an object has because of its motion, equal in classical mechanics to half its mass times speed squared. Changes in motion can be measured as changes in joules of kinetic energy.
Kilowatt-hour: A unit of energy equal to the energy transferred by one kilowatt of power over one hour. Electricity bills use kilowatt-hours, each equal to 3.6 million joules.
Mechanical equivalent of heat: The quantitative relationship between mechanical work and heat, expressed as the work equivalent of a unit of heat. Joule’s experiments helped establish that heat and mechanical work are interconvertible forms of energy.
First law of thermodynamics: The thermodynamic statement of energy conservation, relating changes in internal energy to heat and work. Its energy balance expresses heat and work in the same unit.

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