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energy

Capacity for doing work. This work may be as simple as reading a book, using a computer, or driving a car. Without energy no activity is possible. Energy can exist in many different forms. For example, potential energy (PE) is energy deriving from position; thus a stretched spring has elastic PE, and an object raised to a height above the Earth's surface, or the water in an elevated reservoir, has gravitational PE. Moving bodies possess kinetic energy (KE). Energy can be converted from one form to another, but the total quantity in a system stays the same (in accordance with the conservation of energy principle). Energy cannot be created or destroyed. For example, as an apple falls it loses gravitational PE but gains KE. Although energy is never lost, after a number of conversions it tends to finish up as the kinetic energy of random motion of molecules (of the air, for example) at relatively low temperatures. This is ‘degraded’ energy that is difficult to convert back to other forms.

Energy sources

There are two main sources of energy: the Sun, the ultimate source; and decay of radioactive elements in the Earth. Plants use the Sun's energy and convert it into food and oxygen. The remains of plants and animals that lived millions of years ago have been converted into fossil fuels such as coal, oil, and natural gas.

Energy types and transfer

For energy to be useful it has to be converted into a form that can do work. Energy occurs in many forms – for example, potential (stored energy), kinetic (movement), chemical, heat, light, electrical, sound, and nuclear energy.

A flat battery in a torch will not light the torch. If the battery is fully charged, it contains enough chemical energy to illuminate the torch bulb. When one body A does work on another body B, A transfers energy to B. The energy transferred is equal to the work done by A on B. Energy is therefore measured in joules. The rate of doing work or consuming energy is called power and is measured in watts (joules per second). Energy can be converted from any form into another. A ball resting on a slope possesses potential energy that is gradually changed into kinetic energy of rotation and translation as the ball rolls down. As a pendulum swings, energy is constantly being changed from a potential form at the highest points of the swing to kinetic energy at the lowest point. At positions in between these two extremes, the system possesses both kinetic and potential energy in varying proportions. A weightlifter changes chemical energy from the muscles into potential energy of the weight when the weight is lifted. If the weightlifter releases the weight, the potential energy is converted to kinetic energy as it falls, and this in turn is converted to heat energy and sound energy as it hits the floor. A lump of coal and a tank of petrol, together with the oxygen needed for their combustion, have chemical energy. Other sorts of energy include electrical and nuclear energy, light, and sound. However, all of these types are ultimately classifiable as either kinetic or potential energy.

Resources

So-called energy resources are stores of convertible energy. Non-renewable resources include the fossil fuels (coal, oil, and gas) and nuclear-fission ‘fuels’ – for example, uranium-235. The term ‘fuel’ is used for any material from which energy can be obtained. We use up fuel reserves such as coal and oil, and convert the energy they contain into other, useful forms. The chemical energy released by burning fuels can be used to do work. Renewable resources, such as wind, tidal, and geothermal power, have so far been less exploited. Hydroelectric projects are well established, and wind turbines and tidal systems are being developed.

Energy conservation and efficiency

All forms of energy are interconvertible by appropriate processes. Energy is transferred from one form to another, but the sum total of the energy after the conversion is always the same as the initial energy. This is the principle of conservation of energy. This principle can be illustrated by the use of energy flow diagrams, called Sankey diagrams, which show the energy transformations that take place. When a petrol engine is used to power a car, about 75% of the energy from the fuel is wasted. The total energy input equals the total energy output, but a lot of energy is wasted as heat so that the engine is only about 25% efficient. The combustion of the petrol–air mixture produces heat energy as well as kinetic energy. All forms of energy tend to be transformed into heat and cannot then readily be converted into other, useful forms of energy.

Heat transfer

A difference in temperature between two objects in thermal contact leads to the transfer of energy as heat. Heat is energy transferred due to a temperature difference. Heat is transferred by the movement of particles (that possess kinetic energy) by conduction, convection, and radiation. Heat conduction involves the movement of heat through a solid material by the transfer of vibrational energy from atom to atom. For example, thermal energy is lost from a house by conduction through the walls and windows. Convection involves the transfer of energy by the movement of fluid particles. All objects radiate heat in the form of radiation of electromagnetic waves. Hotter objects emit more energy than cooler objects. Methods of reducing energy transfer as heat through the use of insulation are important because the world's fuel reserves are limited and heating homes costs a lot of money in fuel bills. Heat transfer from the home can be reduced by a variety of methods, such as loft insulation, cavity wall insulation, and double glazing. The efficiencies of insulating materials in the building industry are compared by measuring their heat-conducting properties, represented by a U-value. A low U-value indicates a good insulating material.

E = mc²

Mass can be converted into energy under certain conditions, according to Einstein's theory of relativity. This conversion of mass into energy is the basis of atomic power. Einstein's special theory of relativity (1905) correlates any gain, E, in energy with a gain, m, in mass, by the equation E = mc², in which c is the speed of light. The conversion of mass into energy in accordance with this equation applies universally, although it is only in nuclear reactions that the percentage change in mass is large enough to detect.

Burning fossil fuels causes acid rain and is gradually increasing the carbon dioxide content in the atmosphere, with unknown consequences for future generations. Nuclear power stations do not release carbon dioxide but produce highly dangerous waste that must be disposed of, and pose a small but non-zero risk of a catastrophic release of radioactive material. The ultimate non-renewable but almost inexhaustible energy source would be nuclear fusion (the process by which energy is generated in the Sun), but controlled fusion is a long way off. (The hydrogen bomb is a fusion bomb.) Harnessing resources generally implies converting their energy into electrical form, because electrical energy is easy to convert to other forms and to transmit from place to place, though not to store. Almost a third of all energy consumption in Europe is by transport.

energy

In biology, the basis for conducting living processes. Much of life involves energy transfer. Energy is transferred from the surroundings of an organism into its body, and is also transferred within an organism's body. Energy is used by organisms to do things, such as growing or moving. When they do these things energy is transferred from one substance to another or from one place to another.

An important part of being fit is being able to use energy effectively during exercise to allow muscles to contract.

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energy - events

c. 1420000 BC	Africa	Evidence suggests that Homo erectus at Koobi Fora in Kenya may have used fire.
c. 200 BC	China, Former Han Empire	Coal is first used in China as fuel.
c. 60	Greece	Greek engineer Hero of Alexandria, in his Pneumatica/Pneumatics, describes a primitive steam turbine that he calls an aeolipile; it is the first known device to use steam to produce rotary motion.
1768	Scotland	Scottish engineer James Watt builds a small steam engine with his condenser and the following year takes out a patent on it. This is the first true steam engine.
1794	England	English engineer Robert Street patents the first practical internal combustion engine.
1801	France	French engineer Philippe Lebon lights the Hotel Seignelay in Paris, France, with ‘thermolampes’. It is the first public building to be lit with gas.
c. 1807	England	English chemist Humphry Davy develops the first useable arc lamp; a 2,000-cell battery creates an electric arc across a gap of 100 mm/4 in between two charcoal conductors.
1859	USA	US businessman George Bissell distils kerosene from crude oil and markets it as lamp fuel.
4 September 1882	USA	US inventor Thomas Alva Edison opens the Pearl Street electric generating station in New York City. The first in the USA, it employs three 125 horsepower steam generators to supply direct current (DC) to 225 houses.
30 September 1882	USA	The world's first hydroelectric generating plant opens at Appleton, Wisconsin. It consists of two direct current generators powered by a 107 cm/42 in waterwheel. It produces 2.5 kW of power.
2 December 1942	USA	Italian physicist Enrico Fermi and his colleagues at the University of Chicago, Illinois, use thin layers of uranium oxide and graphite to create the first nuclear pile and initiate a controlled chain-reaction – the first nuclear reactor.
1945	Canada	A nuclear reactor using natural uranium and heavy water as both coolant and moderator (a material that slows down the fission process) begins operating at Chalk River, Ontario, Canada; a second reactor starts operation two years later.
16 July 1945	USA, Japan	The first atomic explosion occurs when the nuclear device code-named ‘Trinity’ is exploded near Alamogordo, New Mexico. On 6 August and 9 August similar devices are dropped on Hiroshima and Nagasaki, Japan.
1951	UK	Two plutonium-production reactors, the first full-scale nuclear reactors in the UK, go into operation at Windscale (known as Sellafield from 1973) in Cumbria, England.
12 December 1951	USA	The first power station in the USA to produce electricity from atomic energy begins operating at Arco, Idaho. Built by the US Department of Energy's Idaho National Engineering Laboratory and known as experimental breeder reactor No. 1 (EBR-I), it is built to demonstrate the feasibility of nuclear power. It generates 300 kW.
10 October 1957	England	A fire in a military reactor producing plutonium at the English nuclear facility Windscale (now Sellafield) releases large amounts of radioactivity into the surrounding area, news of which is suppressed by the UK government.
18 December 1957	USA	The first full-scale commercial nuclear power station in the USA opens at Shippingport, Pennsylvania. It produces 60,000 kilowatts of electricity.
1959	UK	The first fast breeder reactor (that produces more nuclear fuel than it consumes) is commissioned at Dounreay in Scotland.
14 May 1964	USSR, Egypt	The Soviet leader Nikita Khrushchev opens the Aswan Dam in the United Arab Republic (UAR) of Egypt.
1973	world	The Organization of Petroleum Exporting Countries (OPEC) raises oil prices dramatically, causing a worldwide energy crisis. People drive less and turn to more fuel-efficient cars, airlines reduce services, offices turn the heating down, the US president Richard Nixon proposes tax incentives to encourage oil exploration, demand for nuclear power increases, and coal prices rise, giving a boost to the ailing industry.
1974	USA	The energy crisis induced by the oil embargo in the Middle East means that Daylight Savings Time is observed all year round in the USA to save fuel.
29 March 1979	USA	Radioactive material escapes from the nuclear power station at Three Mile Island, Pennsylvania, when the reactor overheats. Fearing a meltdown and the release of radioactive caesium, 144,000 people are evacuated from the immediate area. The accident halts the growing trend towards reliance on nuclear energy in the USA; 11 orders for new reactors are immediately cancelled, with more cancelled the following year.
3 June 1979	Mexico	Pemex Oil's offshore oil-well Ixtoc 1 blows up, releasing an estimated 3 million barrels of crude oil into the Gulf of Mexico. The largest oil spill ever recorded, the slick spreads 965 km/600 mi to Texas, contaminating Gulf fisheries and beaches. The well defies capping efforts and it continues to disgorge oil until 24 March 1980.
1988	Israel, USA	Israeli inventor Herman Branover and the US-Israeli Solmecs firm develop a prototype of a magnetohydrodynamic (MHD) generator that uses molten lead fluid and coal as a fuel, making it suitable for countries that do not have petroleum resources.
August 1995	UK	The world's first commercial wave-powered electricity generator begins operating on the River Clyde, Scotland. Known as ‘Osprey’, it generates 2 megawatts of electricity.
16 April 1998	USA	US scientists at the National Renewable Energy Laboratory develop a solar cell that can split water into hydrogen and oxygen. It is seen as a breakthrough in the generation of alternative fuels.
14 August 2003	USA Canada	One of the worst-ever power failures in North America blacks out the northeastern USA and Canada for hours, prompting government investigations into the US electricity supply system.
28 September 2003	Italy	A massive power failure across Italy brings the whole country with the exception of Sardinia to a standstill for hours. A breakdown of electricity lines from neighbouring Switzerland and France is thought responsible.
25 May 2005	Azerbaijan, Georgia, Turkey	The Baku-Tbilisi-Ceyhan (BTC) oil pipeline, which runs for about 1,800 km from Azerbaijan through Georgia to Turkey's Mediterranean coast, is officially opened. The pipeline was built by a consortium led by BP of the UK at a cost of US$4 billion.

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