Energie

Energy is the capacity to do work or to produce change in a system. In physics, energy is a scalar quantity that can take many forms and be converted from one form to another. The standard unit of energy is the joule (J); for everyday use, the kilowatt-hour (kWh) is common. Work and energy are related by the work-energy principle: energy cannot be created or destroyed, only transformed (the law of conservation of energy).

Common forms include kinetic energy (motion), potential energy (position), thermal energy (related to temperature), chemical energy (stored in chemical bonds), electrical energy, radiant energy (light), and nuclear energy. Energy flow is central to natural processes and human activities, and energy transformations drive devices, engines, and biological systems.

Most energy comes from primary energy sources such as fossil fuels, nuclear fission, and renewables. Primary energy is converted into secondary forms, such as electricity or fuels, for end use. Renewable sources—solar, wind, hydro, geothermal, and biomass—replenish naturally, while non-renewables—coal, oil, natural gas, and uranium—deplete over time and influence environmental outcomes. Energy efficiency and conservation reduce demand, while storage and grids enable reliable supply and balance across time and space.

Global energy systems affect climate, air quality, and economic development. Policies seek to improve energy access, security, and sustainability by promoting efficiency, decarbonization, and innovation.