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  2. Energy - Wikipedia

    en.wikipedia.org/wiki/Energy

    The word energy derives from the Ancient Greek: ἐνέργεια, romanized: energeia, lit. 'activity, operation', [4] which possibly appears for the first time in the work of Aristotle in the 4th century BC. In contrast to the modern definition, energeia was a qualitative philosophical concept, broad enough to include ideas such as happiness ...

  3. Renewable energy - Wikipedia

    en.wikipedia.org/wiki/Renewable_energy

    Renewable energy (or green energy) is energy from renewable natural resources that are replenished on a human timescale. The most widely used renewable energy types are solar energy, wind power, and hydropower. Bioenergy and geothermal power are also significant in some countries. Some also consider nuclear power a renewable power source ...

  4. Energy transition - Wikipedia

    en.wikipedia.org/wiki/Energy_transition

    An energy transition is a broad shift in technologies and behaviours that are needed to replace one source of energy with another. [14]: 202–203 A prime example is the change from a pre-industrial system relying on traditional biomass, wind, water and muscle power to an industrial system characterized by pervasive mechanization, steam power and the use of coal.

  5. Sustainable energy - Wikipedia

    en.wikipedia.org/wiki/Sustainable_energy

    UN Secretary-General Ban Ki-moon Definitions The United Nations Brundtland Commission described the concept of sustainable development, for which energy is a key component, in its 1987 report Our Common Future. It defined sustainable development as meeting "the needs of the present without compromising the ability of future generations to meet their own needs". This description of sustainable ...

  6. Solar energy - Wikipedia

    en.wikipedia.org/wiki/Solar_energy

    The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 122 PW·year = 3,850,000 exajoules (EJ) per year. [12] In 2002 (2019), this was more energy in one hour (one hour and 25 minutes) than the world used in one year. [13] [14] Photosynthesis captures approximately 3,000 EJ per year in biomass. [15]

  7. Equipartition theorem - Wikipedia

    en.wikipedia.org/wiki/Equipartition_theorem

    The (Newtonian) kinetic energy of a particle of mass m, velocity v is given by = | | = (+ +), where v x, v y and v z are the Cartesian components of the velocity v.Here, H is short for Hamiltonian, and used henceforth as a symbol for energy because the Hamiltonian formalism plays a central role in the most general form of the equipartition theorem.

  8. Physics - Wikipedia

    en.wikipedia.org/wiki/Physics

    [25] The most notable ... The development of physics has answered many questions of early philosophers and has raised new questions. ... Heat is a form of energy, the ...

  9. World energy supply and consumption - Wikipedia

    en.wikipedia.org/wiki/World_energy_supply_and...

    If the final energy delivered for consumption is E and the EROI equals R, then the net energy available is E-E/R. The percentage available energy is 100-100/R. For R>10 more than 90% is available but for R=2 only 50% and for R=1 none. This steep decline is known as the net energy cliff. [28]