Glossary

From Thermal-FluidsPedia

Contents 1 A 2 B 3 C 4 D 5 E 6 F 7 G 8 H 9 I 10 J 11 K 12 L 13 M 14 N 15 O 16 P 17 Q 18 R 19 S 20 T 21 U 22 V 23 W 24 X 25 Y 26 Z 27 Sources

A

• absolute humidity: the mass of water vapor in a given volume of air (expressed in grams of water vapor per cubic meter) at atmospheric temperature and pressure.
• absolute zero: the lowest possible temperature at which all atomic motion stops (-273.15° C).
• acidic: a substance with pH lower than 7; the opposite of basic.
• acid rain: rain with a pH less than 5.6.
• adiabatic: the process in which no heat enters or leaves a system.
• aerobic: occurring in presence of oxygen or air. Also see anaerobic.
• albedo: the fraction of the sunlight that is reflected by earth, ice, and cloud back into space.
• algae: plants which grow in moist or aquatic environments.
• alkaline: basic, the opposite of acidic.
• alpha particle: a particle consisting of two neutrons and two protons The nucleus of helium atom. Also see beta particle and gamma ray.
• alternating current (AC): the flow of charge constantly changing direction. Almost all power produced by electric utilities in the United States is AC that shifts direction at a rate of 60 times per second. Also see direct current (DC).
• alternative fuel vehicle (AFV): motor vehicles that run on fuels other than petroleum.
• altitude: the distance above sea-level; the angle between the sun and the horizon. When the sun is on the horizon (sunrise and sunset), this angle is zero. Solar altitude is maximum at solar noon. The complement of solar altitude angle or the angle of the sun from a vertical line directly overhead is called zenith angle.
• amino acid: the complex organic molecules that are the “building blocks” of proteins. Most organisms construct proteins from roughly 20 amino acids.
• amperes (amp): the unit designating the amount of electricity flow through a conductor.
• anaerobic: occurring in the absence of oxygen or air. Also see aerobic.
• anemometer: a mechanical instrument used to measure wind speed

and direction.

• angle of incidence: the angle at which the sun’s rays or insolation strike the earth’s surface.
• anion: an ion carrying a negative charge. Also see cation.
• Antarctic Circle: latitude of 66.5° South. The northern limit of the area of the earth which experiences 24 hours of darkness or 24 hours of daylight at least once during the year. Also see Arctic Circle.
• anthracite: hard coal found deep in the earth containing a high percentage of carbon and little volatile matter. It burns very hot, with little flame.
• anthropocentric: human-centered.
• anthropogenic: human made; usually used in the context of emissions that are produced as the result of human activities.
• aquaculture: aquatic organism farming.
• aquifer: a permeable rock layer that stores a significant amount of water or fluid.
• ash: fine particles of solid or molten rock material ejected during a volcanic eruption or the non-organic, non-flammable substance left over after combustion.
• associated gas: natural gas found in contact with oil in naturally-occurring underground formations. The gas may be present in a free state or dissolved in the petroleum. Also see non-associated gas and dissolved gas.
• atmosphere: the layer of gases that surrounds the earth.
• atom: the smallest unit of an element that still maintains its chemical characteristics.
• atomic mass number: total number of an atom’s protons and neutrons.
• atomic number: the number of protons in the nucleus of an atom.
• atomic mass: the combined weight of an atom’s electrons, protons, and neutrons.
• autotroph: an organism that produces its own food – it does not require outside sources of organic food energy for survival. Also see heterotroph, chemical autotrophs and photosynthetic autotrophs.
• azimuth: the angle between a north-south line on the earth’s surface and the horizontal projection of the sun’s rays, measured from true south. By convention, solar azimuth is negative before noon and positive after noon.

B

• back scattering: the fraction of solar radiation that is directed back into space as a result of particle scattering in the atmosphere.
• bads: opposite of “goods.” Bads are usually referred to anything we have to pay money to dispose of. Examples of bads are air pollutants, garbage, and toxic wastes.
• baghouses: a series of fabric bags that act as filters to remove particulate matter from polluted air.
• barometer: an instrument for measuring atmospheric pressure.
• barrel: 42 U.S. gallons. One barrel of oil has an energy content of 6 million Btu.
• base load: the minimum power production needed during a year.
• basal metabolic rate (BMR): the number of calories a body burns at rest to maintain normal body functions. BMR changes with age, weight, height, gender, diet and exercise habits.
• basic: a substance with a pH greater than 7. Also see acidic.
• battery: a device that stores chemical energy and produces electric current. Batteries are typically built for specific purposes and they differ in construction accordingly. Broadly speaking, there are two applications that manufacturers build their batteries for: starting and deep cycle. Starter batteries have many thin lead plates which allow them to discharge a lot of energy very quickly for a short amount of time. However, they do not tolerate being discharged deeply, as the thin lead plates needed for starter currents degrade quickly under deep discharge and re-charging cycles. Most starter batteries will only tolerate being completely discharged a few times before being irreversibly damaged. Deep cycle batteries have thicker lead plates that make them tolerate deep discharges better. They cannot dispense charge as quickly as a starter battery. Some “marine” batteries are sold as dual-purpose batteries for starter and deep cycle applications. Such batteries should not be cycled deeply and should be avoided for deep-cycle applications unless space/weight constraints dictate otherwise.
• bed: sedimentary structure that usually represents a layer of deposited sediment.
• bedrock: a general term for any consolidated rock.
• beta particle: an electron emitted from the nucleus of a radioactive isotope. Also see alpha particle and gamma ray.
• Bhopal: the city in India where, in December 1984, a major leak at the Union Carbide pesticide facility killed thousands and injured tens of thousands more.
• Big Bang: the theory of the formation of the universe. According to this theory about 15 billion years ago all of the matter and energy in the Universe was concentrated into an area smaller than the size of an atom. At one instance a huge explosion occurred that released an enormous amount of mass that began to expand at an incredible rate and matter, energy, space and time came into being. As the Universe expanded, matter began to coalesce into gas clouds, and then into stars and planets. Some scientists believe that this expansion is finite and will one day cease. After this point in time, the Universe will begin to collapse until a Big Crunch occurs.
• biochemistry: the chemistry of life.
• biodegradable: a matter that can be degraded, decomposed, or broken down by microorganisms into simple compounds such as water and carbon dioxide.
• biodiesel: a fuel derived from vegetables and other organics matter having essentially identical composition to diesel fuel refined from petroleum.
• biodiversity: refers to the diversity of different species (species diversity), genetic diversity among individuals within each species (genetic diversity), and the diversity of ecosystems (ecosystem diversity).

bioengineering: the genetic manipulation of species to produce new varieties and types of organisms.

• biofuel: a fuel made from plants and other biomass.
• biomass: living tissues accumulated over an area in a particular time interval.

biomass energy: energy resources derived from organic matter that include wood, agricultural waste, algae, sewage and other organic substances that can be burned to produce heat or transformed into other fuels through chemical processes.

• biome: a large assemblage of animals and plants that includes many communities of a similar nature.
• biosphere: the layer adjacent to the earth’s surface where all life exists. The biosphere consists of all living things, plant and animal. Also called ecosphere.
• biotic: referring to life, or influenced by living organisms.
• bituminous coal: soft coal of medium quality containing relatively large amounts of carbonaceous matter. Bituminous coal has a heating value somewhat lower than anthracite, and is used primarily for the generation of electricity, production of coke, and space heating. Also see anthracite and lignite.

black body: a body that emits electromagnetic radiation, at any temperature, at the maximum possible rate. It also absorbs all electromagnetic radiation that is falling on it.

• blackout: a power loss affecting many electricity consumers over a large geographical area for a significant period of time, perhaps due to a major breakdown.
• body mass index (BMI): a widely used measurement for obesity calculated as the person’s mass divided by the square of the height.
• boiling water reactor (BWR): a nuclear power plant which is allowed to boil at the core, producing steam which is then used to drive electric turbines.
• bottled gas: the liquefied petroleum gas stored in cylinders under pressure – mainly propane and butane.
• bottoming cycle: a means of increasing the thermal efficiency of a steam electric generating cycle where some waste heat from the condenser is converted into electricity.

breeder reactor: a nuclear reactor that produces more fuel than it consumes. It is especially designed to actively convert non-fissionable isotopes of U-238 into fissionable isotopes of Pu-239 that can then be used as fuel.

• brine: water which contains a large concentration of salt such as a salt lake or seawater.
• British thermal unit (Btu): a unit for measurement of heat defined as the amount of energy required to raise the temperature of one pound of water one degree fahrenheit. One Btu is equal to 252 calories or 1055 joules.
• brown coal: See lignite.
• brownout: when the capacity of a power plant exceeds demand and the voltage to consumers drops by a few percent such that lights often dim.
• buffer: a protective barrier. A substance capable of neutralizing acids and bases and thereby maintaining the original pH of the solution.
• butane: a paraffin with a chemical composition of C4H10. It is used primarily for blending into high-octane gasoline, residential and commercial heating, and manufacturing of chemical and synthetic rubber.

C

• California Energy Commission: a state agency responsible for energy policy in California.
• California Public Utility Commission (CPUC): the administrative agency that regulates privately owned utilities, securing adequate service to the public at rates that are just and reasonable both to customers and shareholders of the utilities. The CPUC also provides electricity and natural gas forecasting, and analysis and planning of energy supply and resources.
• calorie: a unit of heat energy. The amount of heat required to raise the temperature of 1 gram of water 1 degree celsius at standard atmospheric pressure. One heat calorie is equivalent to 4.2 joules. It is common to differentiate heat calories from food calories by using lowercase “c”. Also see *Calorie.
• Calorie: or food calorie equivalent to 1,000 calories. It is common to differentiate food calories from heat calories by capitalizing the “C.” Also see calorie.
• capacity: the amount of electricity produced in an electricity generating station, or the total volume of natural gas that flows through a pipeline over a given amount of time. Capacity of a battery is the amount of usable energy it can store at a nominal voltage.

All other things equal, the greater the physical volume of a battery, the larger its total storage capacity. Capacity is expressed in amp-hour (Ah).

• capacity factor: the fraction of a power plant’s capacity that is utilized on average over time.
• cap-and-trade system: in this system companies are allowed to continue polluting, but must buy the right to pollute more from companies that implement strategies that reduce their pollution.
• carbohydrate: an organic compound composed of carbon, oxygen, and hydrogen atoms, such as sugars, starch, and cellulose.
• carbon auction: companies are allowed to continue polluting, but are required to bid against other companies for a portion of the atmosphere they intend to use -- within guidelines that reduce overall pollution.
• carbon capture and storage (CCS): The process of capturing and storing the CO2 emission at the power plant instead of being released into the atmosphere.
• carbon dating: the process of determining the age of certain archeological artifacts of a biological origin such as bone, cloth, wood and plant fibers.
• carbon dioxide: molecules of a gas composed of one carbon and two oxygen atoms (chemical formula of CO2). Carbon dioxide gas is transparent to solar light but absorbs radiation strongly in the long wave infrared band. This absorption causes the greenhouse effect. It is believed that the higher concentrations of carbon dioxide and other greenhouse gases resulting from human burning of fossil fuels are responsible for global warming.
• carbon monoxide: a colorless, odorless, tasteless and highly poisonous gas made up of one carbon and one oxygen atom formed by the incomplete combustion of carbon or carbonaceous material, including gasoline. The chemical formula for carbon monoxide is CO.
• carbon tax: tax levied on fossil fuels (or any fuels) in proportion to the amount of carbon emitted during combustion.
• carcinogens: any chemical substance in the environment that can potentially cause cancer.
• carnivore: an organism that consumes other living animals. Also see herbivore, omnivore, secondary consumers, and tertiary consumers.
• Carnot efficiency: the highest theoretical efficiency a heat engine can have when operating between the two thermal energy reservoirs at temperatures TL and TH; h = 1 - TL / TH.
• carrying capacity: the maximum population of a species that a certain habitat can support.
• cassandras: doom sayers, those who believe that the exponential growth in populations and consumption will ultimately totally degrade the environment. Cassandras are pessimists, opposite to cornucopians.
• catalytic converter: a device that takes the pollutants emitted by automobile exhausts and smoke stacks (CO, NOx, and hydrocarbon) and converts them to less harmful substances (CO2 and N2).
• catalytic cracking: the process by which the high-boiling fraction of crude petroleum is converted to lighter compounds, distillate, fuel oil and fuel gas using a catalyst and heat.
• cation: an ion carrying a positive atomic charge. See also anion.
• cell: the smallest self-functioning unit of living organisms. Some organisms such as bacteria consist of only one cell, but most of the organisms found on earth are made up of many cells.
• cellulose: the fibrous woody material making up three-quarters of plant material.
• Celsius scale: a temperature scale in which water boils at 100° and freezes at 0°.
• Central American Free Trade Agreement (CAFTA): a trade agreement signed between the United States, Costa Rica, Honduras, Guatemala, and Nicaragua in 2005 under which these countries will remove all trade barriers, tariffs, and quotas between them. Also see North American Free Trade Agreement (NAFTA).
• CFC: acronym for chlorofluorocarbon.
• chain reaction: in nuclear reactions, when the fissioning of one atom releases neutrons that induce the fissioning of other atoms, and so forth. Similarly, in chemical reactions, the release of heat and other radicals results in a release of additional heat and radical species that makes the reaction self-sustaining.
• chemical autotrophs: organisms that use the external energy found in chemical compounds to produce food molecules. The process used to produce food by these organisms is known as chemosynthesis. Also see photosynthetic autotrophs.
• chemical energy: energy stored in molecular bonds. The energy generated when a compound undergoes chemical combustion, decomposes, or transforms to produce new compounds.
• chemosynthesis: a process in which organisms extract inorganic compounds from their environment and convert them into organic nutrient compounds without the use of sunlight. Also see photosynthesis.

chlorofluorocarbons (CFC): artificially produced compounds composed primarily of carbon, fluorine, and chlorine that were introduced in the mid-1930s, used in refrigerants, solvents and insulating foam material. These chemicals were eventually implicated in the deterioration of the ozone layer and subsequently banned.

• chlorophyll: the green pigment in plants and certain bacteria used to capture the energy in light through photosynthesis.
• Clean Air Act: a federal statute enacted in 1963 that was the first of a series of acts and amendments that exerted increasing federal pressure on air polluters to clean up their emissions.
• Clean Water Act: a federal statute enacted in 1972 that has been very successful in improving the water quality of lakes and rivers.
• climate: the general pattern of weather conditions for a region over a long time period.
• closed system: a system that transfers energy but not matter across its boundary to the surrounding environment. Our planet is often viewed as a closed system.
• coal: the black or brown rock, formed under pressure from organic fossils in prehistoric times, that is mined and burned to produce heat energy. Depending on its carbon content coal is classified as anthracite, bituminous, or lignite.
• coefficient of performance (COP): a non-dimensional measure of the ratio of the useful heating (or cooling) load delivered to the corresponding energy input.
• cogeneration: a power plant which produces several types of energy simultaneously – such as electricity and heat – that can be used locally, such as an electric generating station that uses waste heat from its gas turbines to produce steam for conventional steam turbines.
• coke: a porous solid left over after the volatile constituents of coal are driven off by heat in the absence of or in a limited supply of air. It is used primarily in blast furnaces for smelting ores.
• combined cycle plant: See cogeneration.
• compressed natural gas (CNG): natural gas that has been compressed under high pressure, typically between 2,000-3,600 psi, and is held in a container.
• condensation: the change in state of matter from vapor to liquid.
• condensation nuclei: microscopic particles of dust, smoke or salt that act as nucleus for condensation of water vapor to water droplets in the atmosphere. Condensation normally occurs on these particles when relative humidity reaches 100 %.
• condenser: a heat exchanger in which the refrigerant is heated to a high pressure and temperature and then condensed to liquid by rejecting heat.
• conduction: the transfer of heat through a material by the motion of adjacent atoms and molecules without gross displacement of the particles. Also see *convection and radiation.
• conductivity: the ability of a material of a given thickness to transfer heat or electricity.
• constant dollar: the dollar value in which the effect of changes in its purchasing power have been removed.
• consumer: an organism who gets its organic nutrient from the consumption of tissues of producers and other consumers because it cannot synthesize the *organic nutrients in requires. Different consumers are: carnivores, herbivores, and detritivores.
• consumer price index (CPI): an index designed to measure the changes in the prices of goods and services as a ratio of the cost of a bundle of products and services at current prices to its cost at a base year.
• control rod: a rod made of substances such as cadmium or boron with the ability to absorb neutrons used in a nuclear reactor to control or even halt the nuclear chain reaction.
• convection: the transfer of energy by means of mass motions through a medium as a result of a temperature or density gradient. Also see conduction and radiation.
• cooling load: the rate at which heat must be extracted from a space in order to maintain the desired temperature within the space.
• cooling tower: a device for cooling water through direct contact with air.
• core: a layer rich in iron and nickel found in the interior of the earth. It is composed of two sub-layers: the inner core and outer core. The core is about 7,000 kilometers in diameter.
• coriolis force: an apparent force that, as a result of the earth’s rotation, deflects objects to their right in the northern hemisphere and to the left in the southern hemisphere. Coriolis force is responsible for hurricanes, tornadoes, and twisters.
• cornucopians: neoclassical economics who believe that advances in technology result in the growth in living standards which will offset loss of resources and degradation in the environment. Cornucopians are optimists, opposite to cassandras.
• corporate average fuel economy (CAFE): average fuel consumption

in miles per gallon, based on city and highway fuel economy measurements performed as part of the federal emissions test procedures.

• criteria pollutants: pollutants that are mandated by Congress for regulation, including particulate matter, sulfur dioxide, nitrogen dioxide, ozone, lead, and carbon monoxide.
• crude oil: simply called crude, is the petroleum found in the earth before it is refined into oil products.
• cumulative production: the total amount of energy that has been produced so far.
• curb weight: the weight of a vehicle including all standard equipment, spare tire and wheel, all fluids and lubricants to capacity, a full tank of fuel, and the weight of major optional accessories normally found on the vehicle.
• current: a measure of how many electrons are flowing through a conductor. Current is usually measured in amperes (A). Current flow over time is defined as ampere-hours, a product of the average current and the amount of time it flowed.

D

• deep mining: extraction of coal or minerals at great depths. Coal is usually deep-mined at no more than 1,500 feet.
• degree day: a convenient way to measure the energy need for a given day and is calculated by taking the average of the day’s high and low temperatures. The difference between this temperature and the design temperature (taken as 65oF) summed up over all days that require heating (colder than 65oF) is the number of heating degree-days. Similarly, the temperature difference summed up over all days that require cooling (warmer than 65oF) is the number of cooling degree-days.
• demand: the rate at which energy is delivered.
• demand-side management: in economics, the methods used to manage energy demand including energy efficiency, load management, fuel substitution and load leveling. See also supply-side management.
• density: a measure of how tightly the atoms of a substance are packed; mass per unit volume. For gases, density is the number of atoms and molecules per unit volume. Also see specific gravity.
• deoxyribonucleic acid (DNA): the basic hereditary molecule of life on Earth and material of which genes are composed. A form of nucleic acid that is organized into a double-helix molecule. DNA is used by most organisms to chemically code their genetics and to direct the development and functioning of cells.
• depleted uranium (DU): mostly u-238, is a toxic and radioactive waste product of the enriching uranium in nuclear reactors. Because of its high density, DU has been used in manufacturing armored vehicles, missiles warheads, and various ammunitions.

depth of discharge (DOD): a measure of how deeply a battery is discharged. When a battery is 100% full, the DOD is 0%. Conversely, when a battery is 100% empty, the DOD is 100%. For example, starter batteries are not designed to be discharged deeply (no more than 20% DOD). Indeed, if used as designed, they hardly discharge at all; engine starters are very energy-intensive but their duration of use is very short.

• deregulation: elimination of regulation from a previously regulated industry or sector of an industry.
• detritivores: are organisms that recycle detritus (decomposing organic matter), returning it into the food chain.
• deuterium: an isotope of hydrogen with a nucleus containing one proton and one neutron and an atomic mass number of 2.

diffused solar radiation: solar radiation received by the earth’s atmosphere or surface that has been modified by atmospheric scattering.

• diffusion: (1) mixing of one substance into another; (2) refraction of solar insolation in many directions.

diminishing returns, law of: as the supply of a resource declines, increasing efforts to extract the resource produce progressively smaller relative amounts of the resource.

• dioxin: a group of extremely toxic compounds that are inadvertently synthesized in incinerators when trash and garbage are burned.
• direct current: electricity flowing continuously in the same direction. See also alternate current.

direct energy conversion: direct production of electricity from an energy source without transferring the energy to a working fluid or steam. For example, photovoltaic direct solar electricity conversion.

• dissociation: a chemical process where a compound or molecule breaks up into simpler constituents.
• dissolved gas: natural gas dissolved in oil within a reservoir.
• distillation: the desalination of salt water by evaporation so as to remove the dissolved salts.
• diversity: the number of different species in a given region.
• DNA: acronym for deoxyribonucleic acid.
• dose: the amount of ionizing radiation absorbed per unit mass of irradiated material.
• double glazing: windows made of two sheets of glass with an airspace between.
• doubling time: the time it takes a population of a given size growing at a fixed rate, to double in size.
• dry steam: the conventional type of geothermal energy used for electricity production. The principal dry steam resource area is the Geyser in Northern California which is one of only two known areas in the world for dry steam – the other being Larderello, Italy.
• durable goods: material goods or products that are designed to last a relatively long period of time.

E

• ecological footprint: total burden that various human activities puts on the earth.
• ecology: the study of interrelationships of animals and plants to one another and to their environment.
• economic efficiency: a term that refers to the optimal production and consumption of goods and services; occurs when prices of products and services reflect their marginal costs.
• economics: the study of the production, distribution, and consumption of goods and services.
• ecosystem: the interacting system of the biological community and its nonliving environment.
• EER: acronym for energy efficiency ratio.
• efficacy (lighting): the ratio of light from a lamp to the electrical power consumed, expressed as lumens per watt and including ballast losses.
• efficiency: the ratio of what we get to what we put in. Applied to energy, it is the useful energy delivered by a device to the energy supplied to it over the same period or cycle of operation. The first law efficiency is the ratio of useful output to input. The second law efficiency is the ratio of actual output to output under ideal conditions for the same input.
• electric vehicle: a vehicle powered by electricity, usually provided by batteries but may also be provided by photovoltaic (solar) cells or a fuel cell.
• El Niño: the occasional development of warm ocean surface waters along the coast of Ecuador and Peru. El Niño normally occurs around Christmas and usually lasts for a few weeks to a few months. See also La Niña
• electrical generator: a device that converts thermal, chemical or mechanical energy into electricity.
• electric resistance heater: a device that converts electric energy to heat which can be transferred to a space by fans.
• electrical energy: energy resulting from electric current created by a flow of charged particles (electrons).
• electrolysis: the process of breaking a chemical compound down into its elements by passing a direct current through it. Electrolysis of water, for example, produces hydrogen and oxygen.
• electromagnetic energy: energy stored in electromagnetic waves or radiation. Any object with a temperature above absolute zero (-273° C) emits this type of energy. The intensity of energy released is a function of the temperature of the radiating surface. The higher the temperature the greater the quantity of energy released. Electromagnetic radiation covers the entire range of wavelengths or frequencies extending from gamma rays to the longest radio waves and including visible light.
• electron: an elementary particle consisting of a charge of negative electricity equal to about 1.602 x 10-19 coulombs and having a mass of about 9.109534 x 10-28 grams when at rest.
• electrostatic precipitator: a device to remove charged particulates from smoke coming out of a smokestack.
• emigration: the process of leaving one country to take up permanent or semi-permanent residence in another; the opposite process to immigration.
• emission standard: the maximum amount of a pollutant legally permitted to be discharged from a single source.
• emissivity: the ratio of total radiative flux from a body to that of a black body under the same environmental conditions.
• emittance: the energy radiated by the surface of a body per second per unit area. Emittance values range from 0.05 for brightly polished metals to 0.96 for flat black paint.
• energy: the capacity for doing work. Forms of energy include: thermal, mechanical, electrical and chemical.
• energy capacity: the energy delivered in kilowatt hours by battery or an electrical generating station.
• energy density: the energy contained in a given volume of a material (J/m3)
• energy efficiency: in transportation, the ratio of output to input energy expressed in miles traveled per gallon of fuel (mpg).
• energy efficiency ratio (EER): the ratio of cooling capacity of an air conditioning unit in Btu per hour to the total electrical input in watts under specified test conditions.
• energy intensity: in transportation, the ratio of energy input to a process to the useful output from that process; expressed in gallons of fuel per passenger-mile.
• entropy: the measure of the disorder or randomness of energy and matter in a system.
• Environmental Protection Agency (EPA): established in 1970, the U.S. EPA is charged with the task of repairing the damage done to the natural *environment and with establishing new criteria for making a cleaner and healthier environment.
• EPA: acronym for Environmental Protection Agency.
• enzyme: proteins used to facilitate and regulate chemical reactions within living cells.
• equator: the great circle of the celestial sphere whose plane is perpendicular to the axis of the earth. Location on the earth with a latitude of 0°.
• equilibrium: a condition where one or more attributes of a system does not change with time.
• equinox: either of the two times each year when the sun crosses the equator and day and night are of equal length everywhere. The autumnal equinox occurs on the first day of fall (around September 22). The vernal equinox occurs on the first day of spring (around March 21).
• estimated ultimate recovery (EUR): the total amount of a resource that will have been produced from a reservoir when all production ceases. Also see cumulative production and proved reserves.
• estuaries: transitional ecosystems between ocean and freshwater biomes; a partially enclosed coastal area at the mouth of a river where nutrient rich fresh water meets with salty ocean water.
• ethanol: otherwise known as ethyl alcohol, alcohol, or grain-spirit is a colorless, volatile, flammable liquid C2H5OH that is the intoxicating agent in liquors and is also used as a solvent. In transportation, ethanol is used by itself as a vehicle fuel (E100 – 100% ethanol by volume), blended with gasoline (E85 – 85% ethanol by volume), or as a gasoline octane enhancer and oxygenate (10% by volume).
• euphotic zone: The upper, illuminated zone of aquatic ecosystem (meaning well-lit in Greek).
• EV: See electric vehicles.
• evaporation: the change of state from the liquid to vapor phase.
• evaporative cooling: cooling by exchange of latent heat from water sprays, jets of water, or wetted material.
• evolution: a process in which the whole universe is a progression of interrelated phenomena . Biological evolution concerns with the process of change in living organisms during the history of life on earth.
• externality: cost borne by people who are not party to the transaction that imposes upon them.

F

• Fahrenheit scale: a scale for measuring temperature. In this scale, water boils at 212° and freezes at 32°.
• fault: a crack or fracture in the earth’s surface in which there has been movement of one or both sides relative to the other. Movement along the fault can cause earthquakes or, in the process of mountain-building, can release underlying magma and permit it to rise to the surface as a volcanic eruption.
• Federal Energy Regulatory Commission (FERC): an independent regulatory commission within the U.S. Department of Energy that has jurisdiction over energy producers that sell or transport fuels for resale in interstate commerce; the authority to set oil and gas pipeline transportation rates and to set the value of oil and gas pipelines for rate making purposes; and regulates wholesale electric rates and hydroelectric plant licenses.
• feedback loop: a process referring to a circle of causes and effects that connects an effect of a particular action to changes in its surroundings, which in turn influences further action. If the effect tends to reinforce that action, then feedback is positive. On the other hand if this cause and effect relationship tends to be self-limiting, then feedback is negative. An example of a positive feedback is the process of global warming. An example of a negative feedback is the operation of a thermostat.
• ferrel cell: three-dimensional atmospheric circulation cell located at roughly 30 to 60° North and South of the equator.
• fertile: in nuclear industry refers to nuclides that do not directly undergo induced fission but from which fissile material is generated. For example, uranium-238 is not fissionable itself, but can be fissionable by absorbing a fast neutron and convert to plutonium-239.
• FFV: acronym for flexible fuel vehicle.
• fissile: in nuclear industry refers to nuclides capable of sustained chain reaction and fission. The three most important fissile materials are uranium-233, uranium-235, and plutonium-239.
• fission: the release of energy from the splitting of an atom’s nucleus. This is the energy process used in conventional nuclear power plants to make the heat needed to run steam electric turbines. Also see fusion.
• fissionable material: any material with atoms that can undergo nuclear fission. Uranium-238 is a fissionable material but not fissile.
• flare gas: natural gas that is burned as it is released from an oil field. No energy is collected from this process.
• flat plate collector: a device used to collect solar energy; made of a piece of metal painted black on the side facing the sun, to absorb the sun’s heat. The heat can be transferred to a liquid and then used as desired (for instance, to heat a building).
• flexible fuel vehicle (FFV): a vehicle that can operate on either alcohol fuels (methanol or ethanol) or regular unleaded gasoline or any combination of the two from the same tank.
• flue gas: gas that is left over after fuel is burned and which is disposed of through a pipe or stack to the outer air.
• fluidized bed combustion: a process where coal is pulverized (turned into powder) and then carried by a stream of air and burned. The process reduces sulfur dioxide emissions from coal combustion.
• fog: droplets composed of water, ice crystals or smoke particles.
• food chain: the movement of energy through the trophic levels of organisms. In most ecosystems, this process begins with photosynthetic autotrophs (plants) and ends with carnivores and herbivores.
• food web: the complex patterns of energy flow in an ecosystem that describe the interrelationships by which organisms consume other organisms.
• fossil: the remains of living organisms, such as hard and soft parts of plants and animals, tracks and burrows, whole organisms preserved intact in amber or tar, and fossilized dung.
• fossil fuels: carbon based remains of organic matter that has been geologically transformed into coal, oil and natural gas.
• freezing: the change in state of matter from liquid to solid, such as the formation of ice from liquid water.
• Freon: See chlorofluorocarbons.
• fuel: a substance that can be burned to produce heat.
• fuel cell: a device that converts the chemical energy of a fuel directly into electricity. The principal components of a fuel cell are catalytically activated electrodes for the fuel (anode) and the oxidant (cathode) and an electrolyte to conduct ions between the two electrodes. Electrons are bypassed through an external wire which constitutes an electric current.
• fuel reprocessing (nuclear): the means for obtaining usable, fissionable material from spent reactor fuel.
• fuel rod (nuclear): a long slender tube that holds fissionable fuel. Fuel rods are assembled into bundles called fuel elements or assemblies, which are loaded individually into the reactor core.
• fumarole: a vent or opening in a volcanic region from which hot gases and vapors escape.
• fusion: the combining of isotopes of light elements to form a heavier element, the process of which releases heat and electromagnetic radiation energy. Also see fission.
• fusion energy: a technology, presently under development, where atoms are combined under the most extreme heat and pressure. It is the energy process of the sun and the stars.

G

• gamma radiation: ionizing radiation with a wavelength less than 0.03 nanometers that readily penetrates the body tissues of organisms.
• gasohol: gasoline that contains 10 percent ethanol by volume.
• GDP: See gross domestic product.
• gene: organic material responsible for passing inheritance or traits. In most organisms these adaptations are coded through the organic molecule DNA.
• genetic code: The sequence of rules by which DNA constructs the genes.
• generator: See electric generator.
• geostrophic wind: wind in the upper atmosphere that moves parallel to isobars.
• geothermal energy: energy with its origin in the internal heat of the earth.
• glacier: the accumulation of snow and ice developed over a long time period.
• glazing: a covering of transparent or translucent material (typically glass or plastic) used for admitting light.
• global warming: the warming of the earth’s average global temperature because of an increase in the concentration of greenhouse gases.
• glucose: the simple six-carbon sugar with chemical formula C6H12O6.
• GNP: See gross national product.
• gradient: the steepness of a slope as measured in degrees, percentage, or the rise/run ratio.
• gravity: the tendency of one mass to attract another mass. First proposed by Newton in 1686, the force of attraction is found to be proportional to the product of the objects’ masses and inversely proportional to the distance that separates them.
• greenhouse effect: the characteristic tendency of some transparent materials (such as glass) to transmit short wavelength solar radiation and block radiation of longer wavelengths (such as heat). This tendency leads to a heat build-up within the space enclosed by such a material. In the atmosphere, *greenhouse effect refers to the warming of the lower atmosphere due to the accumulation of greenhouse gases that trap heat near the surface of the earth. See global warming.
• greenhouse gases: gases responsible for the greenhouse effect. These gases include: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); chlorofluorocarbons (CFCs; and ozone (O3). These gases allow visible and ultraviolet light (shortwave radiation) to pass through the atmosphere but block (long wave) infrared radiation from being re-emitted by the earth. In the last few centuries, the activities of humans have caused the concentration of the major greenhouse gases to increase, raising the earth’s average temperature. As a result, temperature has already increased by 0.3 to 0.6° C, since the beginning of this century.
• grid: a network of interconnected power lines and generators that is managed so that the generators are dispatched as needed to meet the requirements of the customers connected to the grid at various points.

The electric utility companies’ transmission and distribution system that links power plants to customers through high power transmission line service (110-765 kilovolts [kV]); high voltage primary service for industrial applications and street rail and bus systems (23-138 kV); medium voltage primary service for commercial and industrial applications (4-35 kV); and secondary service for commercial and residential customers (120-480 V). Grid can also refer to the layout of a gas distribution system of a city or town in which pipes are laid in both directions in the streets and connected at intersections.

• gross domestic product (GDP): the total market value of all goods and services produced in a country in a given calendar year.
• gross national product (GNP): the total market value of the goods and services produced by a nation before deduction or depreciation charges and other allowances for capital consumption which is widely used as a measure of economic activity. In the United States, GNP is calculated quarterly by the Department of Commerce.
• gulf stream: the warm ocean current that originates in and around the Caribbean and flows across the North Atlantic to northwest Europe.

H

• half-life: the time required for one half of the nuclei in a radioisotope to disintegrate. Half-lives for radioisotopes range from a few millionths of a second to several billion years.
• halon: chemical compound containing fluorine, bromine, chlorine, or iodine used in fire fighting. Halons, like chlorofluorocarbons, are considered destructive of the earth’s ozone shield.
• hazardous waste: wastes that are particularly dangerous or destructive in one or more of the following ways: ignitable, corrosive, reactive, or toxic.
• heat: a form of energy representing the aggregated internal energy of the motion of atoms and molecules in a body.
• heat capacity: the amount of energy necessary to raise the temperature of a given mass by one degree. Heat capacity may be calculated by multiplying the mass by the specific heat.
• heat engine: an engine that converts heat to mechanical energy. Examples are automobile engines, jet engines, and power plants.
• heat gain: an increase in the amount of thermal energy in a space, resulting from direct solar radiation, heat flow through walls, windows, and other building surfaces, and the heat given off by people, lights, equipment, and other sources.
• heat loss: a decrease in the amount of thermal energy in a space, resulting from heat flow through walls, windows, the roof and other building surfaces and from infiltration of cold outside air.
• heat pump: a device for transferring heat from a low-temperature medium (outside air in the winter) to a high temperature one (air inside the house).
• heat transfer: energy transferred from one object to another because of the temperature difference between them. Heat is commonly transferred by conduction, convection, and radiation.
• heating load: the rate at which heat must be added to a space in order to maintain the desired temperature within the space.
• heating value: the amount of heat given off by the complete combustion of a unit mass of fuel.
• herbicide: a chemical substance used to kill plant weeds.
• herbivore: animals that consume plants. Also known as a primary consumer. Also see omnivore and carnivore.
• hertz: a unit of electromagnetic wave frequency equal to one cycle per second.
• heterotroph: an organisms that cannot produce their own food. Also see autotrophs.
• horsepower: a unit of power equal to 746 watts.
• hot dry rock: an impermeable subsurface rock 5,000 meters or more below the earth’s surface heated by geothermal energy.
• hot spot: an area of exceptionally high species richness or concentration (e.g. near a power plant or smoke stack).
• hybrid vehicle: a vehicle with two or more power sources, normally an internal combustion engine together with an electric propulsion system.
• hydrocarbon: organic compound composed primarily of hydrogen and carbon atoms.
• hydroelectric power: or hydropower is electricity produced by falling water that turns a turbine generator.
• hydrosphere: oceans and other waters of the earth.
• hydrothermal reservoir: an underground zone of porous rock containing hot water and dry steam.

I

• IAEA: acronym for the International Atomic Energy Commission.
• immigration: the process of entering one country from another to take up permanent residence. Opposite of emigration.
• incineration: the burning of trash and garbage at high temperatures in a large furnace for its disposal and to generate electricity.
• independent power producer (IPP): companies or individuals who construct electricity-generating plants and then sell the electricity to an electric utility at wholesale prices. The utility then resells this power to end-use customers. IPPs usually do not own transmission lines to transmit the power that they generate. Although IPPs generate power, they are not franchised utilities, government agencies or qualifying facilities.
• independent system operator (ISO): a neutral operator responsible for maintaining instantaneous balance of the grid system. The ISO performs its function by controlling the dispatch of flexible plants to ensure that loads match resources available to the system.
• indigenous energy resources: power and heat derived from sources native to a region. These include geothermal, hydro, biomass, solar and wind energy. The term usually is understood to include cogeneration facilities.
• industrial smog: air pollution resulting from various industrial activities, consisting of a combination of sulfur dioxide, suspended droplets of sulfuric acid, and a variety of suspended solid particles. Also see photochemical smog.
• infiltration: the uncontrolled leakage of air through cracks and gaps in the building around windows, doors and duct systems.
• infrared radiation: low-energy, long-wavelength (between 0.7 and 100 micrometers) electromagnetic radiation perceived by humans as heat.
• inner core: the inner region of the earth’s core made of solid iron and nickel. The inner core has a diameter of about 1,200 kilometers.
• insolation: the total amount of solar radiation (direct, diffuse, and reflected) that is received by the earth’s surface.
• instability: atmospheric condition where a parcel of air is warmer than that of the surrounding air, causing it to rise in the atmosphere.
• installed capacity: also called the nameplate capacity is the total manufacturer-rated capacities of equipment such as turbines, generators, condensers, transformers, and other system components.
• Intergovernmental Panel on Climate Change (IPCC): a large, international group of officials, scientists, and other researchers who, under the auspices of the United Nations, have been investigating the issue of global climate change, particularly potential future global warming.
• internal combustion engine: an engine in which fuel is burned inside. Examples are cars’ gasoline or rotary engines. Also see external combustion engine.
• International Atomic Energy Commission (IAEA): an international agency under auspices of the United Nations, established in 1957. The agency is responsible for monitoring international nuclear activities and helping nations with safe, secure and peaceful nuclear technologies.
• investor owned utility (IOU): a privately owned, for-profit company that provides a utility, such as water, natural gas or electricity, to a specific service area. A designation used to differentiate a utility owned and operated for the benefit of shareholders from municipally owned and operated utilities and rural electric cooperatives.
• ion: an atom or group of atoms that carries either a positive (cation) or negative (anion) electrical charge.
• ionizing radiation: the emission of alpha or beta particles or gamma rays from radioisotopes that can dislodge one or more electrons from atoms they strike. The free electrons can form charged ions in living tissue that can react with and damage cells or cause cancer.
• ionosphere: a region in the atmosphere above 50 kilometers from the earth’s surface where relatively large concentrations of ions and free electrons exist. The ionosphere is important in communications because it redirects AM radio transmissions, and thus extends the range that radio transmissions can travel.
• IOU: acronym for investor owned utility.
• IPP: acronym for independent power producer.
• ISO: acronym for independent system operator.
• isotope: a form of an element where the number of neutrons in its atomic nucleus is different than the number of protons.
• isotopic dating: dating technique used to determine the age of a rock and mineral through the decay of radioactive elements. Also see carbon dating.

J

• joule: a unit of work or energy equal to the amount of work done when the point of application of force of 1 newton is displaced 1 meter in the direction of the force. It takes 1,055 joules to equal a British thermal unit. It takes about 1 million joules to make a pot of coffee.

K

• Kelvin scale: a scale for measuring temperature. In this scale absolute zero is 0 kelvins, water boils at 373.15 kelvins and freezes at 273.15 kelvins.
• kerogen: the bituminous material in shale which yields oil when heated.
• kerosene: a petroleum distillate suitable for use as an illuminant when burned in wick lamps.
• kilocalorie (kcal): a unit of energy equal to 1,000 calories.
• kilopascal (kPa): a unit of pressure equal to 1,000 pascals. 1 atm=100 kPa.
• kilowatt (kW): a unit of electrical power equal to 1,000 watts. Typical homes, with central air conditioning and other equipment have a demand of 1-5 kW.
• kilowatt-hour (kWh): the most commonly-used unit of electricity consumed over time, i.e., one kilowatt of electricity supplied for one hour.
• kinetic energy: the energy of motion.

L

• La Niña: very strong tropical Pacific trade winds in the central and eastern Pacific Ocean. Also see El Niño.
• land breeze: surface winds blown from land to water during the night. Also see sea breeze.
• landfill gas: gas generated by the natural decomposition of municipal solid waste by anaerobic microorganisms in sanitary landfills. The gases produced, carbon dioxide and methane, can be collected by a series of low-level pressure wells and can be processed into a medium Btu gas that can be burned to generate steam or electricity.
• last mile delivery: the delivery (communication fiber, electrical wiring, or gas pipeline) from the public network to private houses and firms.
• latent heat: the energy required or released when a substance changes phase without changing its temperature. Latent heat of fusion is the amount of energy absorbed during melting or released during freezing. Latent heat of vaporization is the amount of energy absorbed during vaporization or released during condensation.
• latitude: a north-south measurement of position on the earth, measured in degrees, minutes, and seconds. A line connecting all places of the same *latitude is termed a parallel. Latitude ranges from (0°) at the equator to 90° north and 90° south at the north and south poles.
• lava: the molten magma released from a volcanic vent or fissure.
• law of conservation of energy: this law (also called the first law of thermodynamics) states that energy can neither be created nor destroyed, but only transferred from one form to another. Thus, the total amount of energy available in the universe is constant.
• leeward: the side facing away from the wind. Opposite of windward.
• lever: a bar than can move freely around a fixed position. There are three kinds of levers. In the first class lever, the fulcrum is between the force and the weight (shovel, seesaw, and scissors). When the weight is between the fulcrum and the force, the lever is called a second class lever (tweezers, wheelbarrow). In third class levers the force is located between the fulcrum and the weight (baseball bat).
• life cycle analysis: also called the cradle-to-grave analysis, analyzes the entire “life cycle” of a product, from procurement of the raw materials through its use, to its eventual disposal and the possible reuse or recycling of its components. Life cycle cost is the amount of money necessary to own, operate and maintain a building over its useful life.
• life expectancy: the average number of years that a typical person at a certain age can expect to live.
• light duty vehicles: combined automobiles and light trucks.
• light water reactor (LWR): a nuclear power unit that uses ordinary water as the coolant and the moderator. A LWR may be a boiling water reactor or a pressurized water reactor.
• light year: the distance that light travels in a vacuum in one year. It is approximately 9.7 trillion kilometers.
• lignin: amorphous polymer making up about a quarter of plant material that provides rigidity and together with cellulose forms the woody cell walls of plants and the cementing material between them.
• lignite: also called brown coal, is the coal with carbon content somewhere between that of bituminous coal and peat. The texture of the original wood is often visible in lignite.
• limestone: the sedimentary rock composed of carbonate minerals.
• liquefaction: the process of making synthetic liquid fuel from coal. The term is also used to refer to a method for making gasoline and heating oil from petroleum.
• liquefied natural gas (LNG): a mixture of gaseous hydrocarbons, mainly propane and butane, that change into liquid form under moderate pressure.
• liquefied petroleum gas (LPG): the same as propane. LPG is commonly used as a fuel in rural homes for space and water heating, as a fuel for barbecues and recreational vehicles, and as a transportation fuel.
• lithosphere: the rigid crust of the earth.
• LNG: See liquefied natural gas.
• load: the amount of electric power supplied to meet one or more of end user’s needs.
• load factor: a percent telling the difference between the amount of electricity a consumer used during a given time span and the amount that would have been used if the usage had stayed at the consumer’s highest demand level during the whole time. The term is also used to mean the percentage of capacity of an energy facility - such as a power plant or gas pipeline -- that is utilized in a given period of time. In transportation, it means the total passenger miles divided by total vehicle miles (or average number of passengers per vehicle).
• load management: strategies taken to reduce power demand at peak load times or to shift some of the load to off-peak times. Load management may be pursued by persuading consumers to modify behavior or by using equipment that regulates electric consumption.
• longitude: a west-east measurement of position on the earth measured in degrees, minutes, and seconds. A line connecting all places of the same *longitude is termed a meridian. Measurements of longitude range from the prime meridian (0°) to 180° west and 180° east from this point.
• low emission vehicles (LEV): vehicles certified by the California Air Resources Board, or another similar agency, to have emissions from zero to 50,000 miles no higher than 0.075 g/mi of non-methane organic gases, 3.4 g/mi of carbon monoxide, and 0.2 g/mi of nitrogen oxides. Emissions from 50,000 to 100,000 miles may be slightly higher.
• LPG: See liquefied petroleum gas.

M

• magma: the molten rock beneath the earth’s crust. To extract energy from magma resources requires drilling near or directly into a magma chamber and circulating water down the well in a convection- type system.
• magneto hydrodynamics (MHD): a means of producing electricity directly by moving liquids or gases through a magnetic field.
• mantle: the zone of the earth below the crust and above the core.
• marginal cost: in economics is the cost to the utility of providing the next increment of product or service.
• market failure: when market prices do not reflect all the true costs of a product or service (externalities).
• mass number: the total number of neutrons and protons in the nucleus of an atom. Approximate measure of the mass of an atom. Also see atomic number.
• mean solar day: the time it takes to complete one earth rotation relative to the sun (for example, from midnight to midnight). This measurement takes 24 hours and is longer than a sidereal day because it includes the effect of the earth’s revolution around the sun.
• mechanical efficiency: the ratio of the mechanical energy output to the mechanical energy input.
• mechanical work: the work associated a force acting in the direction of motion.
• melting: the process of conversion of solids to liquids.
• meridian: a circular arc passing through poles. All points on the same meridian have the same longitude.
• metabolism: enzymatic reactions performed by the cells of a living organism.
• methane: a light hydrocarbon and the main component of natural gas and marsh gas. It is the product of the anaerobic decomposition of organic matter, fermentation in animals and is one of the greenhouse gases. The primary sources for methane are from rice cultivation, domestic grazing animals, termites, landfills, coal mining, and oil and gas extraction. The chemical formula for methane is CH4.
• methanol: also known as methyl or wood alcohol is a colorless highly toxic liquid with essentially no odor and very little taste. Methanol is formed by steam reforming natural gas, by the distillation of wood, or the catalytic reaction of carbon monoxide (CO) with hydrogen (H2), under high temperature and pressure. Methanol is the simplest alcohol and has the chemical formula of CH3OH. In transportation, methanol is used as a vehicle fuel by itself (M100), or blended with gasoline (M85).
• methyl alcohol: a common liquid hydrocarbon fuel that is also called methanol and is used in some gasoline blends. It has the chemical formula of CH3OH.
• methyl tertiary butyl ether (MTBE): a clean-burning oxygenate with high octane and low volatility added to unleaded gasoline to reduce carbon monoxide emissions. It is one of the primary ingredients in reformulated gasoline.
• microwave: electromagnetic radiation with a wavelength between 0.1 to 100 centimeters. It falls between infrared and radio wavelengths on the electromagnetic spectrum.
• midpoint: the point at which half of ultimate production has been consumed.
• moderator: a substance like water, graphite, or beryllium used in a nuclear reactor to slow down fast neutrons.
• molecule: a minute particle that consists of connected atoms of one or many elements.
• monopoly: a situation where one firm controls market sales. A monopoly can produce a given level of output at a lower total cost than can any combination of multiple firms.
• Montreal Protocol: an international agreement reached in 1987 at a meeting in Montreal, Canada, whereby a number of industrialized countries pledged to freeze CFC production at 1986 levels and then gradually decrease its production until it was eliminated 1999.
• mountain breeze: the local thermal circulation pattern in mountainous areas, where surface winds blow from areas of higher elevation to valley bottoms during the night. The reverse happens during the day.
• MTBE: acronym for methyl tertiary butyl ether.
• municipal solid waste: locally collected garbage, which can be processed and burned to produce energy.
• mutation: the change in the structure of a gene or chromosome.

N

• NAFTA: See North American Free Trade Agreement.
• natural gas: gas commonly found in the pores of sedimentary rocks of marine origin, composed mainly of methane, but also containing ethane, butane, propane and other gases.

neap tide: a tide that occurs every 14 to 15 days and coincides with the first and last quarter of the moon. This tide has a small tidal range because the gravitational forces of the moon and sun are perpendicular to each other. Contrasts with spring tide.

• negative feedback: the change in the state of a system that counteracts the effect of the initial alteration.
• net primary productivity: total amount of chemical energy fixed by the processes of photosynthesis minus the chemical energy lost through respiration.
• neutron: an atomic sub-particle found in the nucleus of an atom. This particle is similar in mass to a proton but does not have a charge.
• newton: the force required to accelerate a mass of 1 kg by 1 m/s2.
• nitric acid: acid formed as a result of the interaction of nitric oxides with water. It has the chemical formula HNO3.
• nitrogen fixation: the biological or chemical process where gaseous nitrogen is converted into solid forms of nitrogen. Biological fixation is done by specialized microorganisms like bacteria. Chemical fixation occurs at high temperatures. One natural process that can produce enough heat to fix atmospheric nitrogen is lightning.
• nitrogen oxides (NOx): oxides of nitrogen produced by the burning of fossil fuels. Nitrogen oxides consist mainly of two gases: nitric oxide (NO) and *nitrogen dioxide (NO2). These gases are produced by bacterial action in the soil and by high temperature combustion. Both gases are chief components of air pollution and responsible for the production of photochemical smog.
• node: a point in a network where electricity can be supplied to the network or withdrawn from it.
• non-associated gas: natural gas that is not trapped with petroleum in the same reservoir. Also see associated gas.
• non-ionizing radiation: a form of electromagnetic radiation that does not have enough energy to cause ionization of atoms in living tissue. Examples of this type of radiation include radio waves, microwaves, infrared light, and ordinary light. See also ionizing radiation.
• non-renewable resource: a resource that is finite in quantity and is being used faster than its ability to regenerate itself. Fossil fuels are a prime example of nonrenewable energy sources.
• North Atlantic Free Trade Agreement (NAFTA): trade agreement signed between the United States, Mexico, and Canada in 1992 in which the three countries agree to remove all trade barriers, tariffs, and quotas between them. Also See Central American Free Trade Agreement (CAFTA).
• NOx: acronym for nitrogen oxides.
• nuclear energy: energy stored in the nucleus of atoms. Power obtained by splitting heavy atoms (fission) or fusing light atoms (fusion). A nuclear energy plant uses a controlled atomic chain reaction to produce heat. The heat is used to produce steam which runs conventional turbine generators.
• Nuclear Regulatory Commission (NRC): an independent federal agency that ensures strict standards of public health and safety, environmental quality and *national security are adhered to by individuals and organizations possessing and using radioactive materials. The NRC is the agency that is mandated with licensing and regulating nuclear power plants in the United States. It was formally established in 1975 after its predecessor, the Atomic Energy Commission was abolished.
• nucleic acid: an organic compound composed primarily of carbon, hydrogen, nitrogen, oxygen, and phosphorus. DNA or deoxyribonucleic acid, the genetic blueprint of life, is an example of a nucleic acid.
• nucleus: the dense central portion of an atom that is composed of neutrons and protons.

O

• octane: a rating scale used to grade gasoline according to its antiknock properties. A measure of gasoline’s resistance to self-ignition too early in the engine cycle, which causes knocking. The higher the octane rating, the lower the chance of premature ignition.
• OECD: acronym for the Organization for Economic Cooperation and Development. OECD is an international organization established in 1948 to stimulate growth among the member states in Europe, the United States, Canada, Mexico and Japan.
• OEM: acronym for original equipment manufacturer.
• ohm: a unit of measurement of electrical resistance. One volt can produce a current of one ampere through a resistance of one ohm.
• oil: the hydrocarbon-based liquid commonly found in the pores of sedimentary rocks of marine origin.
• oil shale: a type of rock containing organic matter kerogen that produces oil when heated to high temperatures.
• OPEC: acronym for the Organization of Petroleum Exporting Countries.
• open system: a system that allows transfer of both matter and energy across its boundary.
• organic matter: matter that contains living organisms or non-living material derived from organisms.
• organic molecule: Any molecule containing carbon and involved in forming life. Carbon dioxide and carbonate minerals are not considered to be organic.
• organism: any form of life.
• Organization of Petroleum Exporting Countries (OPEC): founded in 1960 to unify and coordinate petroleum polices of its members. OPEC headquarters is in Vienna, Austria. OPEC currently has 13 members which include Saudi Arabia, Iran, Venezuela, Libya, Indonesia, United Arab Emirates, Algeria, Nigeria, Ecuador, Gabon, Iraq, Kuwait, and Qatar.
• original equipment manufacturer (OEM): one who manufactures complex systems from components usually bought from other manufacturers.
• outage: See blackout.
• outer core: the outer region of the earth’s core which is 2,300 kilometers thick and composed of liquid molten metals, mostly iron but also some nickel. Temperature of the outer core is relatively uniform, and varies from 5,000oC to about 4,000oC at the edges of the outer core.
• overhang: any horizontal projection that serves as a shading element for a window in summer.
• oxidation: the process of combining with oxygen.
• oxygenate: a method for blending oxygen-rich liquids into gasoline in order to convert carbon monoxide to carbon dioxide and to better oxidize volatile *organic compounds. The increased oxygen content given by oxygenates promotes more complete combustion, thereby reducing tailpipe emissions. Also see reformulated gasoline.
• ozone: a triatomic form of oxygen. It is formed naturally in the atmosphere by photochemical processes. Ozone is a poisonous gas, and in the lower atmosphere an air pollutant. In the upper atmosphere, ozone acts as a shield protecting life on earth from deadly ultraviolet radiation from space.
• ozone hole: a sharp seasonal decrease in stratospheric ozone concentration that occurs over Antarctica and much of the world. First detected in the late 1970s, the ozone hole continues to appear as a result of a complex chemical reaction in the atmosphere that involves chlorine and bromine atoms.
• ozone layer: a layer in the stratosphere containing ozone, most concentrated at an altitude between about 12 and 16 miles (20-25 km). This layer is important to life on the earth as it absorbs harmful ultraviolet radiation.

P

• particulate matter (PM): small particles of either a solid or a liquid that form smoke or soot.
• pascal: the unit of pressure defined as newtons per square meter (N/m2 ). One atmosphere is approximately 100 kilopascals.
• passive solar system: a solar heating or cooling system that uses no external mechanical power to move the collected solar heat. Examples of passive solar systems are common glass, solar roofs, and solar chimneys.
• PCB: or polychlorinated biphenyls is a group of organic compounds used in the manufacture of plastics and formerly used as a coolant in electric transformers. In the environment, PCBs are highly toxic to aquatic life.
• peak load: the amount of electricity needed at the time of highest demand. Daily electric peaks on weekdays occur in the late afternoon and early evening. Annual peaks occur on hot summer days.
• peak load power plant: the power generating station used to produce the extra electricity during peak load times. Also called peaking unit.
• peaking capacity: the capacity of generating equipment intended for operation during the hours of highest loads.
• peat: partially decomposed remains of organic matter that have accumulated in a water-saturated environment over a very long period of time. Geologically, peat is considered a very young form of coal and has a heating value of 6,600 Btu/pound in situ.
• periodic table: a table that arranges chemical elements to describe their chemical properties.
• permafrost: the zone of permanently frozen water found in high latitude soils and sediments.
• permeability: a measure of the ability of soil, sediments, and rock to transport water. Permeability is dependent on the porosity of the medium the water is flowing through. Some rocks like granite have very poor permeability. Sand is the most pervious, while clay has the lowest permeability; silt is somewhere in the middle.
• Persian Gulf: the waterway bounded by the countries of Iran, Iraq, Bahrain, Kuwait, Qatar, Saudi Arabia, and United Arab Emirates.
• petrochemicals: chemicals made from oil.
• petroleum: a generic term applied to oil and oil products.
• phases of matter: matter can exist in three different forms: gas, liquid, and solid.
• pH scale: a scale that is used to measure acidity; a pH of 7.0 is neutral, lower numbers are acidic, higher numbers are basic (alkaline).
• photocell: See photovoltaic.
• photochemical pollutant: a pollutant produced when sunlight initiates chemical reactions among NOx, volatile organic compounds, and other substances found in the air. Also see secondary pollutant.
• photochemical smog: a condition that develops when primary pollutants (oxides of nitrogen and volatile organic compounds created from fossil fuel combustion) interact under the influence of sunlight to produce a mixture of hundreds of different and hazardous chemicals known as secondary *pollutants. Also see industrial smog.
• photon: a discrete packet of radiant energy.
• photosynthesis: the chemical process whereby green plants and some bacteria can capture the energy of the sun and synthesize organic compounds from water and carbon dioxide.
• photovoltaic: a semiconductor device that converts light directly into electricity.
• plankton: a collective term for a variety of marine and freshwater organisms that drift on or near the surface of the water.
• plate tectonics: the theory that the earth’s lithosphere is divided into numerous plates that are in motion relative to each other; the continents ride on the backs of the plates and thus move (“drift”) over geologic time.
• plutonium: a heavy element containing 94 protons. Fissionable isotopes of this element can be used as fuel in nuclear reactors and can also be manufactured into bombs.
• pollutant standards index (PSI): an index defined as a measure of air quality. Index of 100 is assigned to moderate air quality. Higher numbers indicate poorer air quality.
• population density: the number of individuals of a particular species per unit found in a specified area.
• positive feedback: the process in which a system responds to change in a way that magnifies the initial change.
• potential energy (gravitational): the stored energy of a body by virtue of its position.
• power: the work performed in unit time, measured in watts or horsepower (h.p.).
• power (electrical): the product of voltage and current, measured in watts. Power over time is usually defined in watt-hours (Wh), the product of the average number of watts and time. Your energy utility usually bills you per kilowatt-hour (kWh), one of which is 1,000 watt-hours.
• power (mechanical): the product of force and velocity. Alternatively it can be calculated by dividing work by the time it takes to perform that work.
• power (thermal): a measure of the amount of heat flow in unit time. It is often expressed in kJ/hour, kW, or Btu/hr.
• power density: power per unit volume (W/m3) or per unit area (W/m2); in engines, it usually implies power per unit volume of engine or gas turbine. In wind power industry, it refers to power per unit rotor area. When we discuss biomass resource, we often refer to the power generated per unit area of the land mass.
• power plant: a central station generating facility that converts some form of energy into electrical energy.
• ppm (parts per million): a common unit of concentration of gases or vapor in air. For example, 1 ppm of a gas means that 1 unit of the gas is present for every 1 million units of air.
• predator: a consumer organism who feeds on prey.
• pressurized water reactor (PWR): a method of producing nuclear power, cooled by water at elevated pressure to keep it from boiling when it reaches high temperatures.
• prevailing wind: the dominant direction that a wind blows from.
• primary carnivore: See secondary consumer.
• primary consumer: organisms that subsists on the producers (plants) for nourishment, usually herbivores.
• primary pollutant: air pollutants that enter the atmosphere directly from the source such as tailpipes and smoke stacks. Also see secondary pollutant.
• primary producer: organisms that occupy the first trophic level in the grazing food chain. These organisms are photosynthetic autotrophs.
• producer: any of various organisms (like a green plant) which produce their own food by photosynthesis and may become food sources for other organisms.
• propane: also known as LPG is a hydrocarbon gas molecule consisting of three atoms of carbon and eight atoms of hydrogen, and one of the constituents of natural gas.
• protein: organic substances primarily composed of carbon, hydrogen, nitrogen, and some other minor elements which are arranged in about 20 different compounds known as amino acids. The various amino acids found in a protein are linked together by peptide bonds.
• proton: a positively-charged elementary particle identical to the nucleolus of a hydrogen atom.
• pumped hydroelectric storage: a system where excess power is used to pump water to a reservoir during off-peak periods. During peak periods, the reservoir is used to operate auxiliary hydroelectric generators.
• PX: the California Power Exchange Corporation; a state chartered, non-profit corporation charged with scheduling and providing markets for energy and ancillary services. PX is independent of the ISO and all other market participants.

Q

• quad: one quadrillion (1015 Btu), an amount of energy equal to 170 million barrels of oil.
• qualifying facility (QF): non-utility power producers that generate electricity using renewable and alternative resources, such as hydro, wind, solar, geothermal or biomass (solid waste). Under federal law, QFs have the right to sell their excess power output to the public utilities.

R

• rad (radiation adsorbed dose): a unit for measuring absorbed radiation. One rad equals 100 ergs of radiation energy per gram of absorbing material.
• radiant energy: energy transferred by the exchange of electromagnetic waves from a hot or warm object to one that is cold or cooler. In some cases it refers to the radiation emitted from the sun.
• radiation: the flow of energy via electromagnetic waves such as light.
• radioactive decay: the natural decay of the nucleus of an atom.
• radioactivity: a property of isotopes of atoms from a nucleus as it disintegrates. In the process some elementary particles (such as alpha and beta particles) and energy (such as gamma rays) are emitted.
• radioisotope (radioactive isotope): an unstable isotope of an element.
• radiometer: an instrument used to measure radiation over a range of wavelengths.
• ramp: a slanted surface used to lift a weight.
• Rankine cycle: the steam-cycle consists of a boiler, a steam turbine, a condenser, and a pump.
• reformer: a device for on-board production of hydrogen.
• reformulated gasoline: a cleaner-burning gasoline with the oxygenate additive MTBE.
• refrigerant: a fluid such as R-134a or ammonia. Refrigerants are usually gas at room temperatures but turn into liquid at temperatures considerably colder than the ambient.
• refuse: refers to both trash and garbage.
• remediation: efforts to reduce effects of pollution after it has been released into the environment.
• renewable energy sources: resources that will regenerate within a human time scale and are regarded as practically inexhaustible. These include solar, wind, hydro, ocean thermal, and wood. Geothermal is considered renewable by some and non renewable by others depending on the time the reservoir needs to recharge itself.
• reserve capacity: the extra generating capacity of an electric utility to meet peak or abnormally high demands for power, or when other generating units are off-line for maintenance, repair or refueling.
• reserves: a retainer or holder of a resource for use at a future time. Natural resources that have been discovered and can be exploited for profit. Proved reserves are reserves that are expected to be recovered from future explorations, and which can be produced economically through application of improved recovery techniques. Inferred reserves (or indicated reserves) are estimates of the amount of reserve growth.
• residential sector: private households consuming energy primarily for space heating and cooling, water heating, refrigeration, lighting, cooking, etc.
• resistance: the ability to resist the flow of heat or current. Resistance depends on the cross section of the conductor (the smaller the cross section, the greater the resistance) and its temperature (the hotter the cross section, the greater its resistance). Also see conductance.
• resource: known or inferred available sources of energy supply that are not exploitable for profit. Conventional resources are discrete concentrations of resources that can be extracted using traditional methods. Examples of conventional resources are petroleum products such as gasoline and kerosene. Unconventional resources are resources whose technical development is in relatively early stages, and which require practices different from traditional production methods. Examples of unconventional resources are shale oils and tar-sands.
• respiration: the process of the “burning” of food molecules in an organism to release the energy required for all metabolic processes. Also see photosynthesis.
• restructuring: the separation of the various utility functions into several individually-operated and individually-owned entities (such as generation, distribution, and retail).
• retail market: a market in which electricity and other energy services are sold directly to the end-use customer.
• ribonucleic acid (RNA): a form of nucleic acid used by most organisms to read the genetic information found in DNA and to produce specific organic molecules used in the development and functioning of cells.
• rocket: a device where a solid or liquid fuel and an oxidizer react in the combustion chamber producing high-pressure combustion gases that are then expanded in a nozzle, producing the thrust to propel the rocket.
• rubbish: a general term that includes trash, garbage, and other items such as construction and demolition debris.
• R-value: a unit of thermal resistance used for comparing insulating values of different materials. The higher the R-values, the greater the material’s insulating properties and the slower heat flows through it.

S

• salinity: concentration of dissolved salts in water.
• scattering: the atmospheric process where small particles and gas molecules diffuse rays of the incoming solar radiation in random directions without changing their wavelengths.
• screw: an inclined plane wrapped around a cylinder or a cone.
• sea breeze: surface winds blown from water to land during the daytime. Also see land breeze.
• second law of thermodynamics: See thermodynamics (laws of).
• secondary consumer: animals that feed on the primary consumers.
• secondary pollutants: pollutants not emitted directly from the source but formed after primary pollutants and other components of the air react, mainly with ozone. Also see primary pollutants.
• secondary standards: an air-quality standard designed to protect property, vegetation, etc. as opposed to health.
• sedimentary rock: a rock formed on or near the earth’s surface by the settling or precipitation of materials.
• shale oil: See oil shale.
• shrub: a woody plant species that is smaller than a tree. Shrubs usually do not have a trunk.
• sick building syndrome: syndrome resulting from indoor air pollutants in a building with symptoms such as headaches, nausea, and allergic reactions.
• sidereal day: the time it takes the earth to make one complete rotation relative to the position of a fixed star. This measurement takes 23 hours and 56 minutes. Also see solar day.
• silt: mineral particles with a diameter between 0.004 and 0.06 millimeters.
• smog: a mixture of smoke and fog, mostly a brown haze of photochemical pollutants. Also see photochemical smog.
• sin tax: euphemism for a tax levied on certain activities, which are subject of widespread disapproval - usually alcohol and tobacco.
• SOC: See state of charge.
• soil permeability: the rate at which a fluid moves vertically through the soil.
• soil porosity: the ratio of the volume of voids to the total volume of the soil.
• solar cell: a photovoltaic cell that can convert light directly into electricity. A typical solar cell uses semiconductors made from silicon.
• solar collector: a device that absorbs solar energy to heat a fluid. The heated fluid can be used directly or used to heat water or space.
• solar concentrator: the process of concentrating sunlight on a relatively small area.
• solar day: the time it takes earth to complete one rotation relative to the sun. Also see sidereal day.
• solar energy: thermal and light energy radiated from the sun.
• solar irradiation: the amount of radiation, both direct and diffuse, that can be received at any given location.
• solar noon: the time of the day when the sun is aligned with true north and true south. Half-way between sunrise and sunset.
• solar power satellite: a proposed process of using satellites in geosynchronous orbit above the earth to capture solar energy with photovoltaic cells, convert it to microwave energy, beam the microwaves to earth where they would be received by large antennas and changed from microwaves into usable electricity.
• solar radiation: electromagnetic radiation that originates from the sun. Also see insolation, direct solar radiation, and diffused solar radiation.
• solid waste: garbage, trash, refuse, and rubbish that result from mining, agricultural, commercial, and industrial activities.
• specific energy: energy per unit mass (J/kg). In batteries, it is defined as the rated energy capacity of a battery divided by the total battery system weight; measured in watt-hours per kilogram.
• specific gravity: the ratio of the mass of a body to the mass of an identical volume of water at a specific temperature. Also see density.
• specific heat: the amount of heat needed to raise the temperature of one gram of a substance one degree celsius. In US customary units, the quantity of heat, in Btu, needed to raise the temperature of one pound of material one degree fahrenheit.
• spectrum: radiation emitted from a body at different wavelengths.
• speed of light: the velocity of light in a vacuum (3 x 108 meters per second).
• spring tide: a tide that occurs every 14 to 15 days and coincides with the new and full moons. During this time, tides have the largest range because the gravitational forces of the moon and the sun are complementary to each other. Also see neap tide.
• state of charge: describes how full a battery is charged. The exact voltage to battery charge correlation is dependent on the temperature of the battery. Cold batteries will show a lower voltage when full than hot batteries.
• Stirling engine: an external combustion engine which works by heating (expanding) and cooling (contracting) a captive gas such as helium or hydrogen.
• strategic petroleum reserve: stockpiles of government-owned crude oil stored at various reserves that can be drawn on during emergencies and severe oil supply disruptions. A reserve of 750 million barrels of oil is available that can be released only by the order of the President of the United States.
• stratosphere: the thermal layer of the atmosphere above the troposphere (11 to 50 kilometers above the earth’s surface) in which temperature increases with altitude. The ozone layer exists within the stratosphere. Also see troposphere.
• strip-mining: the surface mining of minerals and resources such as coal.
• subatomic particles: extremely small particles that make up the internal structure of atoms.
• sublimation: the change in phase of matter directly from solid to vapor without passing through the liquid state. Examples of substances undergoing *sublimation at standard temperatures and pressures are dry ice and iodine.
• subsidence: the sinking of the earth’s surface.
• substation: an intermediary facility that steps up or steps down the voltage in utility power lines. Voltage is stepped up where power is sent through long-distance transmission lines. It is stepped down where the power is to enter local distribution lines.
• sulfur dioxide: a colorless gas consisting of two atoms of oxygen and one atom of sulfur (SO2) found in volcanic eruptions, ocean spray, organic decomposition and the products of burning fossil fuels. Once in the air, in the presence of water vapor, it forms sulfuric acid mist that can be found in fogs or precipitated as rain or snow.
• superconductor: a synthetic material that has very low or no electrical resistance. A major research effort is underway to find materials that behave as superconductors near room temperature. Once found, electrical transmission lines may be built that offer little or no resistance, thus conserving energy usually lost in transmission.
• supply-side management: in economics, refers to all efforts required to find new resources and processes that improve supply of a natural resource. See also demand-side management.
• surface waves: a special type of seismic wave that travels across the earth’s surface, causing the earth’s surface to roll or sway like waves on the ocean.
• sustainability: means different thing to different people. Neoclassical economists equate it with economic progress, while ecologists define *sustainability as meeting the needs of today’s generation, without reducing the quality of life for future generations.
• sustainable growth: development that focuses on making social, economic, and political progress to satisfy global human needs, desires, aspirations, and potential without damaging the environment; also known as sustainable development.
• syncrude: synthetic crude oil made from coal or from oil shale. Also see synfuel.
• synfuel: synthetic gas or synthetic oil. Fuel made by artificial means (in contrast to that which is found directly in nature). Also see syncrude.

T

• temperature: a measure of the average speed of atoms and molecules.
• therm: a unit of energy equal to 100,000 Btu, mostly used to express amounts of gas consumption.
• thermal conductivity: See conductivity.
• thermal efficiency: the ratio of work output to energy input.
• thermal energy: See heat.
• thermal power plant: any electrical generating facility using heat to boil water or another working fluid to turn it into vapor or steam used to run a generator. Examples of thermal power plants are oil, coal, gas, nuclear, and geothermal. Wind, hydroelectric, or solar photovoltaic electrical generating facilities are not considered thermal plants.
• thermal storage: a material with high specific heat capable of storing energy. Typical thermal mass materials include concrete, rock, brick, and water.
• thermocline: the transition layer of water between the mixed warm layer at the surface and the cold deep water.
• thermodynamic equilibrium: a condition where all nonuniformities (temperature, pressure, density, electric potential, etc.) have smoothed out.
• thermodynamics (laws of): the fundamental laws of nature dealing with quantitative and qualitative aspects of energy. The three laws of thermodynamics are: the first law of thermodynamics, which states that energy may be transformed from one form to another, but its total remains constant; the second law of thermodynamics, which states that heat cannot be converted completely to work; and the third law of thermodynamics, which states that heat capacity and entropy of every crystalline solid becomes zero at a temperature of absolute zero, which is impossible toreach.

thermodynamics: the study of the conversion of energy into other forms and of their practical applications.

• tidal current: an ocean current created by the tidal rise and fall of the ocean surface.
• tidal period: the time it takes for one tidal cycle (between two high tides).
• tide: the cyclical rise and fall of the surface of the oceans caused by the gravitational attraction of the sun and moon on the earth.
• ton of refrigeration: the cooling effect equal to 12,000 Btu/hour
• transformer: an electronic device used to raise or lower one electric potential to another.
• transportation sector: private and public vehicles including automobiles, buses, trucks, motorcycles, railroads, aircrafts, ships, barges, and natural gas pipelines.
• trophic level: a group of organisms that occupy the same position in a food chain.
• tropical rainforest: the plush forested biome near the equator.
• tsunami: a large ocean wave formed as a result of underwater seismic activities or volcanic eruption. Its height is rather small, about 1 meter in open oceans, but reaches over 15 meters in height when it enters shallow coastal waters.

U

• ultraviolet radiation: electromagnetic radiation with a wavelength between visible and x-ray (0.1-0.4 micrometers).
• updraft: air current with upward velocity.
• upper mantle: the layer of the earth’s interior between lower mantle and crust.
• uranium: a radioactive element, commonly used as fuel in fission reactors.
• utility: an entity that owns or operates facilities for generation, transmission, distribution, or sale of electricity; a regulated, vertically-integrated electric company.

V

• valley breeze: the wind pattern which develops as a result of non-uniform heating between the valley to areas of higher elevation.
• vapor: the state of a compound at temperatures above its boiling point..
• vapor pressure: the pressure exerted by vapor molecules at a given temperature.
• vernal equinox: the time when the sun crosses the equator and day and night are of equal length everywhere, indicating the start of spring. It occurs around March 21 or 22.
• viscosity: a measure of resistance to flow in a fluid due to intermolecular friction.
• visibility: the distance that a large object can be seen with naked eyes.
• visible radiation: the electromagnetic radiation visible to naked human eyes.
• volatile organic compounds (VOCs): organic molecules mainly composed of carbon and hydrogen atoms.
• volt: the unit of electromotive force. It is the amount of force required to drive a steady current of one ampere through a resistance of one ohm. The power delivered to homes and offices is 120 volts in the U.S. and 220 volts in Europe.
• voltage: the potential to perform work through electricity.

W

• watt: a unit of power in SI units, named after James Watt. 1W =1 J/s.
• watt-hour: a metric unit of energy; defined as power expended over one hour.
• wave: to swing back and forth or up and down. Waves are characterized by their amplitude (vertical distance between a wave’s trough and crest), *wavelength (distance between two successive wave crests or troughs), and period (the time it takes for a wave to travel the distance of one wavelength).
• wedge: a moving inclined plane.
• well: a shaft or hole sunk to obtain oil, brine, or gas. An exploratory well (or dry hole) is drilled to assess justification for completion of an oil or gas well. A development well is a well drilled within the proved area of an oil or gas reservoir. A service well is a well drilled for the purpose of supporting production in an existing field. Examples are gas, water, steam, or air injections, and salt-water disposal.
• wind: motion of air relative to earth as a result of a pressure or temperature difference.
• wind chill factor: the temperature that still air would have to be to result in the same sensation as a combination of wind and temperature on naked human flesh.
• windward: the side facing the direction from which wind is blowing. See also leeward.
• winter solstice: the shortest day of the year or first day of winter (around December 21 or 22).
• work: the energy required to displace a force by a distance along the direction of force.

X

• x-ray: electromagnetic radiation with a wavelength between gamma rays and ultraviolet radiation.

Y

• Yucca Mountain: the proposed site in Nevada where a permanent repository for nuclear waste is being built. It is scheduled to open for operation in 2010.

Z

• zenith: the highest point reached in the heavens by a celestial body. The complement of solar altitude angle or the angle of the sun from a vertical line directly overhead is called zenith angle. Also see altitude.
• Zeroth Law of Thermodynamics: See Laws of Thermodynamics

Sources

1. Encarta, Online Encyclopedia. (http://encarta.msn.com). 2. Wikipedia, The Free Encyclopedia (http://wikipedia.org). 3. Merriam Webster Encyclopedia (http://www.m-w.com). 4. British Britannica (http://www.britannica.com). 5. Department of Energy Websites (http://www.doe.gov). 6. Department of Transportation Website (http://www.dot.gov). 7. British Petroleum Website (http://www.bp.com). 8. Fundamentals of Physical Geography, Pidwirny, M., University of British Columbia Okanagan, Canada VIV 1V7. (http://www.physgeog.net).