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In physics, energy (from Ancient Greek ἐνέργεια (enérgeia) 'activity') is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat and light. Energy is a conserved quantity—the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement for energy in the International System of Units (SI) is the joule (J).
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object (for instance due to its position in a field), the elastic energy stored in a solid object, chemical energy associated with chemical reactions, the radiant energy carried by electromagnetic radiation, and the internal energy contained within a thermodynamic system. All living organisms constantly take in and release energy.
Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy.
Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The Earth's climate and ecosystems processes are driven by the energy the planet receives from the Sun (although a small amount is also contributed by geothermal energy). (Full article...)
To avoid dangerous climate change, the energy policy of the European Union has set a 2°C [3.6°F] limit to the temperature rise, compared to pre-industrial levels. Of this, 0.8°C has already taken place and another 0.5°C is already committed. The 2°C rise is associated with a carbon dioxide concentration of 400–500 ppm by volume; as of January 2007 it was 383 ppm by volume, and rising at 2 ppm annually. Unless significant action is taken soon the 2°C limit is likely to be exceeded.
Strategies for moving to a low-carbon economy include development of new technologies, particularly renewable energy; electric and hybrid vehicles; fuel cells; public transportion; zero-energy buildings; Zero-Net-Energy USA Federal Buildings; energy conservation; carbon taxes; enhancing natural carbon dioxide sinks; population control; and carbon capture and storage. Environmental groups also encourage individual-lifestyle and political action, as well as action by business.
The Kyoto Protocol, covering more than 160 countries and over 55% of global emissions provides an international mitigation framework. The United States, the world's largest greenhouse gas emitter; and Kazakhstan have refused to ratify the treaty. China and India, two other large emitters, have ratified the treaty but are exempt from cutting emissions. International talks on a successor to the treaty, which ends in 2012, have begun.
Photo credit: Postdlf
Lightning is a highly visible form of energy transfer.
In 1831, Faraday began his great series of experiments in which he discovered electromagnetic induction. He established that a changing magnetic field produces an electric field, a relation mathematically modelled by Faraday's law. Faraday later used the principle to construct the electric dynamo, the ancestor of modern power generators. He went on to investigate the fundamental nature of electricity, concluding in 1839 that, contrary to opinions at the time, only a single "electricity" exists, and the changing values of quantity and intensity (voltage and charge) would produce different groups of phenomena.
Some historians refer to Faraday as the best experimentalist in the history of science. Despite this his mathematical ability did not extend so far as trigonometry or any but the simplest algebra. He nevertheless possessed the ability to present his ideas in clear and simple language. During his lifetime, Faraday rejected a knighthood and twice refused to become President of the Royal Society.
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