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Introduction
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...)
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Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of 40,000 MW at the end of 2010. More than 100 countries use solar PV. Installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building (building-integrated photovoltaics).
Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaics has declined steadily since the first solar cells were manufactured. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries.
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Photo credit: From an image by Wolfgang Beyer
Strombolian volcanic eruptions can eject incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters.
Did you know?
- Buildings constructed to the German Passivhaus standard use 75% to 95% less energy for space heating and cooling than current new buildings in the United States?
- Crossing 4,000 km (2,500 miles), the Druzhba pipeline is the world's longest oil pipeline?
- Coal is ground to a powder before being burnt in fossil fuel power plants?
- Compact fluorescent lamps (pictured) use about 1/4 of the energy of normal incandescent light bulbs, and pay for themselves after about 500 hours of use?
- Nuclear power in France produces 78% of all the country's electricity - more than in any other nation?
- Positive lightning bolts are typically six to ten times more powerful than normal lightning — and aircraft are not designed to withstand them?
- Dark energy is a hypothetical form of energy which permeates all of space?
Selected biography
Maxwell studied natural philosophy, moral philosophy, and mental philosophy at the University of Edinburgh, before graduating in mathematics at the University of Cambridge, where he would conduct much of his career. He built on Michael Faraday's work on magnetic induction, using elements of geometry and algebra to demonstrate that electric and magnetic fields travel through space, in the form of waves, and at the constant speed of light. Finally, in 1861, Maxwell proposed that light consisted of undulations in the same medium that is the cause of electric and magnetic phenomena. In the same year he was elected to the Royal Society.
In 1864, Maxwell presented what are now known as Maxwell's equations to the Royal Society. These collectively describe the behaviour of both the electric and magnetic fields, as well as their interactions with matter.
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Quotations
- "We must not waste time and energy disputing the IPCC's report or debating the right machinery for making progress. The International Panel's work should be taken as our sign post: and the United Nations Environment Programme and the World Meteorological Organisation as the principal vehicles for reaching our destination." – Margaret Thatcher, 1990
- "The Kyoto treaty would have wrecked our economy, if I can be blunt." – George W. Bush, 2005
- "We strongly believe that the efforts needed to combat climate change do not have to be regarded as constraints on the economy. Instead, they can be used as a lever for new, green technology." – Maud Olofsson, 2007
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