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In general, the word energy refers to a concept that can be paraphrased as "the potential for causing changes", therefore one can say that energy is the cause of any change. The word is used in several different contexts. The use of the word in mainstream science has a precise, well-defined meaning, which is not the case, most often, with many other usages. The most common definition of energy is the work that a certain force (gravitational, electromagnetic, etc) can do. Due to variety of forces energy has many different forms (gravitational, electric, heat, etc)that can be grouped into two major categories: kinetic energy and potential energy. According to this definition, energy has the same units as work; a force applied through a distance. The SI unit of energy, the joule, equals one newton applied through one meter, for example. Etymology The etymology of the term is from Greek ενέργεια, εν- means "in" and έργον means "work"; the -ια suffix forms an abstract noun. The compound εν-εργεια in Epic Greek meant "divine action" or "magical operation"; it is later used by Aristotle in a meaning of "activity, operation" or "vigour", and by Diodorus Siculus for "force of an engine." Historical perspective The concept of energy, in the distant past, was used to explain easily observable phenomena, such as the effects observed on the properties of objects or any other changes. It was generally construed that all changes can in fact be explained through some sort of energy. Soon the idea, that energy could be stored in objects took its roots in scientific thought and the concept of energy came to embrace the idea of the potential for change as well as change itself. Such effects (both potential and realized) come in many different forms. While in spiritualism they were reflected in changes in a person, in physical sciences it is reflected in different forms of energy itself. For example, electrical energy stored in a battery, the chemical energy stored in a piece of food (along with the oxygen needed to burn it), the thermal energy of a water heater, or the kinetic energy of a moving train. §|}} In 1807, Thomas Young was the first to use the term "energy" instead of vis viva to refer to the product of the mass of an object and its velocity squared. Gustave-Gaspard Coriolis described "kinetic energy" in 1829 in its modern sense, and in 1853, William Rankine coined the term "potential energy." The development of steam engines required engineers to develop concepts and formulas that would allow them to describe the mechanical and thermal efficiencies of their systems. Engineers such as Sadi Carnot and James Prescott Joule, mathematicians such as Émile Claperyon and Hermann von Helmholtz , and amateurs such as Julius Robert von Mayer all contributed to the notions that the ability to perform certain tasks, called work, was somehow related to the amount of energy in the system. The nature of energy was elusive, however, and it was argued for some years whether energy was a substance (the caloric) or merely a physical quantity, such as momentum. William Thomson (Lord Kelvin) amalgamated all of these laws into his laws of thermodynamics, which aided in the rapid development of energetic descriptions of chemical processes by Rudolf Clausius, Josiah Willard Gibbs, Walther Nernst. In addition, this allowed Ludwig Boltzmann to describe entropy in mathematical terms, and to discuss, along with Jožef Stefan, the laws of radiant energy. During a 1961 lecture for undergraduate students at the California Institute of Technology, Richard Feynman, a celebrated physics teacher and a Nobel Laureate, had said "There is a fact, or if you wish, a law, governing natural phenomena that are known to date. There is no known exception to this law—it is exact so far we know. The law is called conservation of energy it states that there is a certain quantity, which we call energy that does not change in manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number, and when we finish watching nature go through her tricks and calculate the number again, it is the same..." This lecture was later published in the Volume 1 of the The Feynman Lectures on Physics. Energy in Natural Sciences The concepts of energy and its transformations are useful in explaining all natural phenomena. The Law of conservation of energy is equally useful. The direction of transformations due to energy changes is often influenced by entropy considerations. Certain forms of energy are often said to be more concentrated than others; using this terminology it can be said that in natural processes energy is transformed from more concentrated forms, to less concentrated and more randomly distributed forms, for example heat. The exact context of various natural phenomena and transformations varies from one natural science to another. Some examples are: Physics The transformations that constitute the context of energy in physics, is the change in position or movement of an object which is brought about through the action of a force. Thus in the context of physics, energy is said to be the ability to do work; the strict mathematical definition of energy in physics always being the amount of work itself (done by or against specified force). Because forces are usually classified by type (gravitational, electrostatic, etc), so also are the specific forms of work these forces produce (or are involved in). For example, a gravitational potential energy is defined as the amount of work to elevate (or lower) a mass against a gravitational force; electrostatic energy is defined as the work done to rearrange electric charges against electric force, kinetic energy is defined as the amount of work to accelerate a body (against force of inertia) to a given velocity, etc. In the simplest language, work is a force multiplied by a distance (more accurately, force integrated over a certain path). The equation above says that the work () is equal to the integral of the dot product of the force () on a body and the infinitesimal of the body's translation (). Depending on the kind of force F involved, work of this force results in a change of the corresponding kind of energy (gravitational, electrostatic, kinetic, etc). Units of energy are thus exactly the same as units of work (=joule in SI). Because work is frame dependent (= can only be defined relative to certain initial state or reference state of the system), energy also becomes frame dependent. For example, a speeding bullet has kinetic energy in the reference frame of a non-moving observer, it has zero kinetic energy in its proper (co-moving) reference frame -- because it takes zero work to accelerate a bullet from zero speed to zero speed. Of course, the selection of a reference state (or reference frame) is completely arbitrary - and usually is dictated to maximally simplify the problem to be dealt with. However, when the total energy of a system cannot be decreased by simple choice of reference frame, then the (minimal) energy remaining in the system is associated with an invariant mass of the system. In this special frame, called the center-of-momentum frame or center-of-mass frame, total energy of the system E and both its invariant mass and relativistic mass m are related by Einstein's famous equation ''E'' = ''mc''². The concept of quantized energy is a product of quantum mechanics. Any system can be described by an Schrodinger equation, and for bound systems the solution of this equation leads to certain permitted states, each characterized by an energy level. In the realm of wave mechanics the energy is related to the frequency of an electromagnetic radiation by the Planck equation E = hν (where h is the Planck's constant and ν the frequency) Chemistry
Biology
Meteorology Meteorological phenomena like wind, rain, hail, snow, lightning, tornados and hurricanes, are all a result of energy transformations brought about by solar energy on the planet Earth. It has been estimated that the average total solar incoming radiation (or insolation) is about 1350 watts per square meter incident to the summit of the atmosphere, at the equator at midday, a figure known as the Solar Constant. Although this amount varies a little each year, as a result of solar flares, prominences and the sunspot cycle. Some 34% of this is immediately reflected by the planetary albedo, as a result of clouds, snowfields, and even reflected light from water, rock or vegetation. As more energy is received in the tropics than is re-radiated, while more energy is radiated at the poles than is received, climatic homeostasis is only maintained by a transfer of energy from the tropics to the poles. This transfer of energy is what drives the winds and the ocean currents. Like biological processes, all meteorological processes involve transformation of energy from a concentrated form such as sunlight into a less concentrated form, such as far infrared radiation (i.e., heat radiation at the much smaller characteristic temperatures that occur on Earth, and thus is diffused into many photons). However, energy may be temporarily locally stored during this process, and the sudden release of such stored sources is responsible for the most dramatic processes mentioned above. Geology Continental drift, mountain ranges, volcanos, and earthquakes are phenomena that are a result of energy transformations in the Earth's crust. Recent studies suggest that the Earth transforms about 6.18 x 10-12 J/s (joules per second) per kilogram. Given the Earth's mass of about 5.97 x 1024 kilograms, this means that the rate of energy transformations inside the Earth is about 37 x 1012 J/s (37 terawatts). From the study of neutrinos radiated from the Earth (see KamLAND), scientists have recently estimated that about 24 terawatts of this rate of energy transformation is due to radioactive decay (principally of potassium 40, thorium 232 and uranium 238) and the remaining 13 terawatts is from the continuous gravitational sorting of the core and mantle of the earth, energies left over from the formation of the Earth, about 4.57 billion years ago. The magnitude of both of them decline over time, and based on half-life alone, it has been estimated that the current radioactive energy of the planet represents less than 1% of that which was available at the time the planet was formed. As a result, geological forces of continental accretion, subduction and sea floor spreading, account for 90% of the Earth's energy. The remaining 10% of geological tectonic energy comes through hotspots produced by mantle plumes, resulting in shield volcanoes like Hawaii, geyser activity like Yellowstone or flood basalts like Iceland. Tectonic process, driven by heat from the Earth's interior, metamorphose weathered rocks, and during orogeny periods, lift them up into mountain ranges. The potential energy represented by the mountain range's weight and height thus represents heat from the core of the Earth which has been partly transformed into gravitational potential energy. This potential energy may be suddenly released in landslides or tsunamis. Similarly, the energy release which drives an earthquake represents stresses in rocks that are mechanical potential energy which has been similarly stored from tectonic processes. The energy which is responsible for the geological processes of erosion and deposition is a result of the interaction of solar energy and gravity. An estimated 23% of the total insolation is used to drive the water cycle. When water vapour condenses to fall as rain, it dissolves small amounts of carbon dioxide, making a weak acid. This acid acting upon the metallic silicates that form most rocks produces chemical weathering, removing the metals, and leading to the production of rocks and sand, carried by wind and water downslope through gravity to be deposited at the edge of continents in the sea. Physical weathering of rocks is produced by the expansion of ice crystals, left by water in the joint planes of rocks. A geologic cycle is continued when these eroded rocks are later uplifted into mountains. Astronomy and cosmology The phenomona of stars, nova, supernova, quasars and gamma ray bursts are the universe's highest-output energy transformations of matter. All stellar phenomena (including of course solar activity) are driven by various kinds of energy transformations. Energy in such transformations is either from gravitational collapse of matter (usually molecular hydrogen) into various classes of astronomical objects (stars, black holes, etc.), or from nuclear fusion (of lighter elements, primarily hydrogen). Light elements, primarily hydrogen and helium, are thought to have been created in the Big Bang, as per the currently accepted theories of cosmology. These light elements were spread too fast and too thinly in the Big Bang process (see nucleosynthesis) to form the most stable medium-sized atomic nuclei, like iron and nickel. This fact allows for later energy release, as such intermediate-sized elements are formed in our era. The formation of such atoms powers the steady energy-releasing reactions in stars, and also contributes to sudden energy releases, such as in novae. Gravitational collapse of matter into black holes is also thought to power the very most energetic processes, generally seen at the centers of galaxies. Cosmologists are still unable to explain all cosmological phenomena purely on the basis of known conventional forms of energy (see next section) and often invoke another form called dark energy to account for certain cosmological observations. Methods of Measurement The methods for the measurement of energy often deploy methods for the measurement of still more fundamental concepts of science, viz. mass, distance, radiation, temperature, time, electric charge and electric current. Conventionally the technique most often employed are calorimetry, in thermodynamics that relies on the measurement of temperature: a thermometer or a bolometer for measurement of intensity of a radiation. Different forms of energy and their inter-relations In the context of natural sciences, energy can be in any of several different forms: thermal, chemical, electrical, radiant, nuclear etc. Some basic textbooks broadly groups all these forms of energy into two broad categories kinetic energy and potential energy. However, some forms of energy resist such easy classification, as is the case with light energy. Other familiar types of energy (such as heat in most circumstances) are a varying mix of both potential and kinetic energy. Kinetic Kinetic energy is energy due to motion of a body or particles within it. Thermal energy, often referred to as heat is a kind of kinetic energy because it is partly because of the motion of atoms or molecules within a solid, liquid or gas. The case of an ideal gas is perhaps one that has been analyzed mathematically in maximum detail. The kinetic energy,ε of the particles that comprise an ideal gas is expressed by the equipartition theorem to be equal to , so the energy per particle is proportional to temperature. For a monatomic gas having N particles each with three degrees of freedom, the internal energy is: where k is the Boltzmann constant and T is absolute temperature. Whereas all internal energy is kinetic in an ideal gas at low temperatures, at higher temperatures in gases, and in liquids and solids, there is more energy in vibrations within the molecules. Thus, whenever there is energy due to vibrations, half of it is stored as kinetic energy and the other half in electromagnetic potential energy between particles. Similarly, radiation energy, also commonly known as light energy, is often portrayed as being carried by moving photons and electrical energy is portrayed as being transferred from one place to another through movement of electrons. However, close examination reveals that this is not really true. Radiation energy cannot be neatly categorized as classical kinetic energy, since photons have no invariant mass and thus the energy required to accelerate them to their velocity (and thus which is associated with their motion) cannot be calculated using other kinetic equations. The electrical energy of an electric current is also not entirely due to the motion of electrons from one end of the conducting wire to another. There is, no doubt, some motion of electrons involved, but its contribution to the total electrical energy is very small. An electric current is in fact induced motion of charges at one end of a wire by introduction of an electric field at the other. It is transfered over a conductor with a speed almost equal to the speed of light, but electron do not move at even a tiny fraction of that speed. The energy of an electric current, is therefore, a result of electric field on the electrons of the conducting wire. This field provides an electric potential energy, measured in volts, for the charged particles that move through the field. In other words, the flow of an electric current is due to the influence of the electric field that produces a force on the moving charges. The application of this force through a distance through which the charges travel, produces work. This electrical work can be transformed into kinetic energy, and other types of energy, such as light or heat. Potential Potential energy is the energy due to the position of an object relative to other objects. It can be visualized as monetary savings or monetary debt. This form of energy can be positive or negative because it can be either work done on an object by a force, or work done by the object against a force. Negative energy is a thus a mathematical construct in reference to another system. For instance, using the power of a compressed spring to launch a dart uses the elastic potential energy stored within the spring. When the spring is released, this energy is converted into kinetic energy, and work is performed. There is a form of potential energy for each of the four basic forces in nature: gravity, electromagnetic, and strong and weak nuclear forces. In the ideal case of a metal spring described by Hooke's Law, the stored elastic energy is equal to: where k is the spring constant, dependent on the individual spring, and x is the deformation of the object. Transformations of energy One form of energy can often be readily transformed into another with the help of a device- for instance, a battery, from chemical energy to electrical energy; a dam: gravitational potential energy to kinetic energy of moving water (and the blades of a turbine) and ultimately to electric energy through a generator. Similarly in the case of a chemical explosion chemical potential energy, is transformed to kinetic energy and thermal energy in a very short time. Yet another example is that of a pendulum. At its highest points the kinetic energy is zero and the gravitational potential energy is at maximum. At its lowest point the kinetic energy is at maximum and is equal to the decrease of potential energy. If one (unrealistically) assumes that there is no friction, the conversion of energy between these processes is perfect, and the pendulum will continue swinging forever. Energy can be converted into matter and vice versa, although both energy and matter continue to exhibit rest mass throughout any such process (thus in a closed system, conversion of matter to energy or energy to matter makes no difference in the system mass). The equation E=mc2, mathematically derived independently by Albert Einstein and Henri Poincaré reflects the equivalence between mass and energy. This equation states that the liberated active energy (light, heat, radiation) that is equivalent to a unit of inactive matter is enormous. This can be witnessed in the tremendous energies liberated by a nuclear bomb. Conversely, the mass equivalent of a unit of energy is miniscule, which is why loss of energy from most systems is difficult to measure by weight, unless the energy loss is very large. Examples of energy transformation into matter (particles) are found in high energy nuclear physics. However, all energy in any form exhibits rest mass, even if it has not been converted into new particles. Law of conservation of energy Energy, in the context of natural sciences, is subject to the law of conservation of energy. According to this law it can neither be created (produced) nor destroyed. It can only be transformed. According to the first law of thermodynamics the total inflow of energy into a system must equal the total outflow of energy from the system, plus the change in the energy contained within the system. This law is used in all branches of physics, but frequently violated for short enough periods of time during which energy can not be mathematically defined yet (see quantum electrodynamics and off shell concept). Noether's theorem relates the conservation of energy to the time invariance of physical laws. This law is a fundamental principle of physics, it follows from the translational symmetry of time, a property of most phenomena below the cosmic scale that makes them independent of their locations on the time coordinate. Put differently, yesterday, today, and tomorrow are physically indistinguishable. The fact that energy can not be defined for arbitrary short periods of time in quantum mechanics follows from the definition of energy operator which results mathematically in the mutual uncertainty of time and energy known as the uncertainty principle: Despite being seemingly insignificant, this principle has made profound impact on our understanding many phenomena in the realm of particle physics. It led to the introduction of the concept of virtual particles which carry momentum, exchange by which with real particles is responsible for creation of all known fundamental forces (more accurately known as fundamental interactions). Virtual photons (which are simply lowest quantum mechanical energy state of photons) are also responsible for spontaneous radiative decay of exited atomic and nuclear states, for the Casimir force, for Van der Waals bond forces and some other observable phenomena. Energy in Society In the context of society the word energy is synonymous to energy resources, it most often refers to substances like fuels, petroleum products and electric power installations. This difference vis a vis energy in natural sciences can lead to some confusion, because energy resources (which represent usable energy) are not conserved in nature in the same way as energy is conserved in the context of physics. People often talk about energy crisis and the need to conserve energy, something contrary to the principle of energy conservation in natural sciences. Efforts, normally referred to as energy conservation, are actually efforts that are targetted at conserving currently available energy resources that can be applied to do useful work. Economics Production and consumption of energy resources is very important to the global economy. All economic activity requires energy resources, whether to manufacture goods, provide transportation, run computers and other machines, or to grow food to feed workers, or even to harvest new fuels. Thus the way in which a human society uses its existing energy resources, develops means of their production or acquisition is a defining characteristic of its economy. The progression from animal power to steam power, then the internal combustion engine and electricity, are key elements in the development of modern civilization. The cost of energy resources depends on its demand and production at any particular time. Scarcity of cheap fuels is a key concern in future energy development. Some attempts have been made to define "embodied energy" - the sum total of energy expended to deliver a good or service as it travels through the economy. Environment Consumption of energy resources, (e.g. turning on a light) is apparently harmless. However, producing that energy requires resources and contributes to air and water pollution. Many electric power plants burn coal oil or natural gas in order to generate electricity for energy needs. While burning these fossil fuels produces a readily available and instantaneous supply of electricity, it also generates air pollutants including carbon dioxide (CO2), sulfur dioxide and trioxide (SOx) and nitrogen oxides (NOx). Carbon dioxide is an important greenhouse gas which is thought to be responsible for some fraction of the rapid increase in global warming seen especially temperature records in the 19th century, as compared with tens of thousands of years worth of temperature records which can be read from ice cores taken in artic regions. Burning fossil fuels for electricity generation also releases trace metals such as beryllium, cadmium, chromium, copper, manganese, mercury, nickel, and silver into the environment, which also act as pollutants. Certain renewable energy technologies do not pollute the environment in the same ways, and therefore can help contribute to a cleaner energy future for the world. Renewable energy technologies available for electricity production include biofuels, solar power, tidal power, wind turbines, hydroelectric power etc. However, serious environmental concerns have been articulated by several environmental activists regarding these modes of electricity generation. According to them, some pollution is invariably produced during the manufacture and retirement of the materials associated with the machinery used in these technologies. A central way to avoid downsides of expanding energy production is energy conservation. Exploration and research Scientists have realized that the known energy resources may not suffice forever, there is thus an urgent need to explore new avenues, which include prospecting for newer territories rich in oil or gas or methods for producing energy resources using methods that have been explored very little.While some scientists are busy in exploring the possibility of cold fusion many countries are diverting significant economic resources towards space exploration *. Space exploration of long duration demands compact energy resources because the huge consumption of energy resources by a large size spacecraft cannot be met by chemical portable energy resources carried on board from the Earth. For missions to the outer solar system, compact nuclear power sources (in the form of nuclear reactors or radioisotope thermoelectric generators) are a necessity. It has been proposed to explore annihilation of matter for this purpose, although no practical way of producing significant amounts of antimatter, or storing them is presently known. Yet another field of research to explore a future source of energy is through artificial photosynthesis, a process being actively researched to convert the carbon dioxide into useful fuel, other than biomass without the intervention of plants. Management Since the cost of energy has become a significant factor in the performance of economy of societies, management of energy resources has become very crucial.Energy management involves utilizing the available energy resources more effectively that is with minimum incremental costs. Many times it is possible to save expenditure on energy without incorporating fresh technology by simple management techniques. Most often energy management is the practice of using energy more efficiently by eliminating energy wastage or to balance justifiable energy demand with appropriate energy supply. The process couples energy awareness with energy conservation. Politics Since energy plays an essential role in industrial societies, the ownership and control of energy resources plays an increasing role in politics at the national level. Governments may seek to influence the sharing (distribution) of energy resources among various sections of the society through pricing mechanisms; or even who owns resources within their borders. They may also seek to influence the use of energy by individuals and business in an attempt to tackle environmental issues. The most recent international political controversy regarding energy resources is in the context of Iraq wars. Some political analysts maintain that the hidden reason for both 1991 and 2003 wars can be traced to strategic control of international energy resources. Others counter this analysis with the numbers related to its economics. According to the latter group of analysts, U.S. has spent about $336 billion in Iraq as compared with a background current value of $25 billion per year budget for the entire U.S. oil import dependence See Energy wars Production Producing energy to sustain human needs is an essential social activity, and a great deal of effort goes into the activity. While most of such effort is limited towards increasing the production of electricity and oil, newer ways of producing usable energy resources from the available energy resources are being explored. One such effort is to explore means of producing hydrogen from water. Though hydrogen use is environmentally friendly, its production requires energy and existing technologies to make it, are not very efficient. Research is underway to explore enzymatic decomposition of biomass. See hydrogen economy. Other forms of conventional energy resources are also being used in new ways. Coal gasification and liquefaction are recent technologies that are becoming attractive after the realization that oil reserves, at present consumption rates, may be rather short lived. See alternative fuels. Transportation While energy resources are an essential ingredient for all modes of transportation in society, the transportation of energy resources is becoming equally important. Energy resources are invariably located far from the place where they are consumed. Therefore their transportation is always in question. Some energy resources like liquid or gaseous fuels are transported using tankers or pipelines, while electricity transportation invariably requires a network of grid cables. The transportation of energy, whether by tanker, pipeline, or transmission line, poses challenges for scientists and engineers, policy makers, and economists to make it more riskfree and efficient. Usage Ever since humanity discovered various energy resources available in nature, it has been busy in inventing devices, commonly known as machines, that make life more comfortable by using one or the other energy resource. Thus, although the primitive man knew the utility of fire to cook food, the invention of very many devices like gas burners and microwave ovens have increased the usage of energy for this purpose alone manifold. The trend is the same in any other field of social activity, be it construction of social infrastructure, manufacturing of fabrics for covering; porting; printing; decorating for example, textiles), air conditioning; communication of information or for moving people and/or goods(automobiles) Warfare Warfare even before the invention of explosives and bombs invariably resulted in comsumption or destruction of huge quantities of energy resources. But ever since the invention of nuclear weapons the potential for such consumption and destruction has increased many-fold. During an attack with a nuclear bomb the destruction of energy resources is phenomenal as was witnessed during the second world war. It has therefore become imperative that such warfare is avoided as far as possible; nuclear non-proliferation treaty is an international initiative in this direction. See also Other links | |||||||||||
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