energia

Energia is a physical quantity that describes the capacity to perform work or to cause changes in systems. In physics, energy is a scalar quantity that can be transformed from one form to another but cannot be created or destroyed in an isolated system, as stated by the law of conservation of energy.

Energy appears in multiple forms, including kinetic energy of moving objects, potential energy associated with position, thermal energy related to temperature, chemical energy stored in bonds, electrical energy, radiant energy from light, and nuclear energy from atomic nuclei. Elastic, sound, and other forms are related representations of these same quantities.

Energy is transferred through work, when a force moves an object, and through heat transfer between bodies at different temperatures. The total energy of an isolated system remains constant, though energy can be redistributed and transformed, with some processes producing dissipation as heat due to irreversibilities.

Measurement: The SI unit is the joule (J). Electricity use is commonly billed in kilowatt-hours (kWh). At the atomic level, energy is often expressed in electronvolts (eV).

Sources and use: Energy is obtained from various sources and can be stored or converted for end use. Primary energy denotes energy contained in natural resources before conversion; final energy is the energy available to consumers after transformation losses. Major categories are fossil fuels, nuclear energy, and renewable sources such as solar, wind, hydro, geothermal, and bioenergy.

Environmental and policy context: Energy systems affect climate, air quality, and resource use. Access to reliable, affordable energy is a common policy objective, while reducing greenhouse gas emissions is a priority in many regions.

Origin of the term: The word energia is used in several languages, including Spanish, Italian, and Portuguese, and derives from Latin energia and Greek energeia, meaning activity or work.