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> General Resources > Glossary
General Resources

Use these general resource documents and activities to help increase your success in this course.

Glossary

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Acceleration The change in velocity divided by the change in time; a = ?v/?t.

Acceleration Due To Gravity Usually given as the symbol g; equal to 9.80 m/s2, or 32 ft/s2.

Average Acceleration The change in velocity divided by the time for the change to occur.

Average Speed The distance traveled divided by the time to travel that distance.

Average Velocity The change in displacement divided by the change in time; v = ?d/?t.

Acceleration Due To Gravity Usually given as the symbol g; equal to 9.80 m/s2, or 32 ft/s2.

Angular Momentum mvr for a mass m going at a speed v in a circle of radius r.

Archimedes? Principle An object immersed wholly or partially in a fluid experiences a buoyant force equal in magnitude to the weight of the volume of fluid that is displaced.

Alternative Energy Sources Energy sources that are not based on the burning of fossil fuels and nuclear processes.

Amplitude The maximum displacement of a wave from its equilibrium position.

Alternating Current (Ac) Electric current produced by constantly changing the voltage from positive to negative to positive, and so on.

Ampere (A) The unit of electric current defined as that current which, if maintained in each of two long parallel wires separated by one meter in free space, would produce a magnetic force between the two wires of 2 × 10-7 newtons for each meter of length.

Atom The smallest particle of an element that can enter into a chemical combination.

Alpha Decay The disintegration of a nucleus into a nucleus of another element, with the emission of an alpha particle.

Atomic Mass The average mass (in atomic mass units, u) of an atom of the element in naturally occurring samples.

Atomic Number Symbolized Z, it is equal to the number of protons in the nucleus of an atom of that element.

Alkali Metals The elements in Group 1A of the periodic table, except for hydrogen (Li, Na, K, Rb, Cs, Fr).

Alkaline Earth Metals The elements in Group 2A of the periodic table (Be, Mg, Ca, Sr, Ba, Ra).

Allotropes Two or more forms of the same element that have different bonding structures in the same physical phase.

Anions Negative ions; so called because they move toward the anode (the positive electrode) of an electrochemical cell.

Acid A substance that gives hydrogen ions (or hydronium ions) in water (Arrhenius definition).

Acid?Base Reaction The H+ of the acid unites with the OH- of the base to form water, while the cation of the base combines with the anion of the acid to form a salt.

Acid?Carbonate Reaction An acid and a carbonate (or hydrogen carbonate) react to give carbon dioxide, water, and a salt.

Activation Energy The energy necessary to start a chemical reaction; a measure of the minimum kinetic energy that colliding molecules must possess in order to react.

Activity Series A list of elements in order of relative ability of their atoms to be oxidized in solution.

Avogadro?S Number 6.02 × 1023, symbolized NA; the number of entities in a mole.

Addition Polymers Those formed when molecules of an alkene monomer add to one another.

Alcohols Organic compounds containing a hydroxyl group, ?OH, attached to an alkyl group; general formula, ROH.

Aliphatic Hydrocarbon A carbon?hydrogen compound that contains no benzene rings.

Alkanes Hydrocarbons that contain only single bonds; general formula, CnH2n+2.

Alkenes Hydrocarbons that have a double bond between two carbon atoms; general molecular formula, CnH2n.

Alkyl Group A substituent that contains one less hydrogen atom than the corresponding alkane; general symbol, R.

Alkyl Halide An alkane derivative in which one or more of the hydrogen atoms have been replaced by halogen atoms; general formula, RX.

Alkynes Hydrocarbons that have a triple bond between two carbon atoms; general molecular formula, CnH2n-2.

Amides Nitrogen-containing organic compounds that have the general formula RCONHR´.

Amine A basic (alkaline) organic compound that contains nitrogen; general formula, RNH2.

Aromatic Hydrocarbon A carbon-hydrogen compound that contains one or more benzene rings.

Altitude The angle measured from the horizon to a celestial object.

Ante Meridiem (A.M.) Pertaining to time from 12 midnight to 12 noon.

Autumnal Equinox The point where the Sun crosses the celestial equator from north to south, around September 22. The beginning of Fall.

Aberration of Starlight The apparent displacement in the direction of light coming from a star that results from the orbital motion of the Earth.

Albedo The fraction of incident sunlight reflected by a body?s surface.

Astronomical Unit (Au) The average distance between the Earth and the Sun, which is 93 million miles.

Astronomy The scientific study of the universe, which is the totality of all matter, energy, space, and time.

Annular Eclipse A solar eclipse in which the Moon blocks out all of the Sun except for a ring around the Sun?s outer edge.

Asteroids Large chunks of matter that orbit the Sun (usually between Mars and Jupiter) and that are too small to be labeled as planets.

Absolute Magnitude The brightness a star would have if it were placed 10 pc (32.6 ly) from the Earth.

Apparent Magnitude The brightness of a star (or other celestial object)as observed from the Earth.

Air Current Vertical air movement.

Anemometer An instrument used to measure wind speed.

Atmospheric Science The investigation of every aspect of the atmosphere.

Acid Rain Rain that has a relatively low pH (i.e., relatively high acidity) because of air pollution.

Air Mass A mass of air with physical characteristics that distinguish it from other air.

Asthenosphere The rocky substratum below the lithosphere that is hot enough to be deformed and is capable of internal flow.

Aquifer A body of permeable rock through which groundwater moves.

Absolute (Numerical) Geologic Time The time of past geologic events, established on the basis of the radioactive decay of certain atomic nuclei.

Amber Fossilized tree resin.






Buoyant Force The upward force resulting from an object being wholly or partially submerged in a fluid.

Btu (British Thermal Unit) The amount of heat required to raise one pound of water one degree Fahrenheit at normal atmospheric pressure.

Beta Decay The disintegration of a nucleus into a nucleus of another element, with the emission of a beta particle.

Base A substance that produces hydroxide ions in water (Arrhenius definition).

Big Bang Theory of the beginning of the universe that states that the known universe was smaller, hotter, and denser in the past, and that it began rapidly expanding 13.7 billion years ago.

Black Hole An object whose gravity is so strong that the escape velocity is equal to or greater than the speed of light; thus no radiation can escape from the object.

Brown Dwarfs Low-mass objects that are larger than a typical planet but do not have enough mass to begin fusion in their cores. Also called ?failed stars.?

Barometer A device used to measure atmospheric pressure.

Bergeron Process The process by which precipitation is formed in clouds.

Bedding The stratification of sedimentary rock formations.






Centi- The metric prefix meaning 1/100, or 0.01.

Conversion Factor An equivalence statement expressed as a ratio.

Centripetal Acceleration The ?center-seeking? acceleration necessary for circular motion; a = v2/r.

Centripetal Force The ?center-seeking? force that causes an object to travel in a circle.

Conservation of Angular Momentum, Law Of The angular momentum of a system remains constant unless acted upon by a net torque.

Conservation of Linear Momentum, Law of The total linear momentum of a system remains constant if there are no external unbalanced forces acting on the system.

Conservation of (Total) Energy, Law Of The total energy of an isolated system remains constant.

Conservation of Mechanical Energy, Law Of In an ideal system, the sum of the kinetic and potential energies is constant: Ek + Ep = E (a constant).

Calorie (Cal) The amount of heat necessary to raise one gram of water one degree Celsius at normal atmospheric pressure.

Celsius Scale A temperature scale with 0°C as the ice point and 100°C as the steam point.

Conduction (Thermal) The transfer of heat energy by molecular collisions.

Convection The transfer of heat through mass movement.

Concave Lens A lens that has the shape of the inside (concave side) of a spherical section.

Concave Mirror A mirror shaped like the inside (concave side) of a small section of a sphere.

Convex Lens A lens that has a surface shape of the outside (convex side) of a spherical section.

Convex Mirror A mirror shaped like the outside (convex side) of a spherical section.

Charges, Law Of Like charges repel, and unlike charges attract.

Coulomb (C) The unit of electric charge, equal to one ampere-second (A·s).

Coulomb?S Law The force of attraction or repulsion between two charged bodies is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.

Curie Temperature The temperature above which ferromagnetic materials ceases to be magnetic.

Current (Electrical) The rate of flow of electric charge; I = q/t.

Carbon-14 Dating A procedure used to establish the age of ancient organic remains by measuring the concentration of 14C and comparing it to that of present-day organic remains.

Chain Reaction Occurs when each fission event causes at least one more fission event.

Critical Mass The minimum amount of fissionable material necessary to sustain a chain reaction.

Chemistry The division of physical science that studies the composition and structure of matter and the reactions by which substances are changed into other substances.

Compound A substance composed of two or more elements chemically combined in a definite, fixed proportion by mass.

Cations Positive ions; so called because they move toward the cathode (the negative electrode) of an electrochemical cell.

Conservation of Mass, Law Of No detectable change in the total mass occurs during a chemical reaction.

Covalent Bond The force of attraction caused by a pair of electrons being shared by two atoms.

Covalent Compounds Those in which the atoms share pairs of electrons to form molecules

Catalyst A substance that increases the rate of reaction but is not itself consumed in the reaction.

Chemical Properties Characteristics that describe the chemical reactivity of a substance?that is, its ability to transform into another substance.

Chemical Reaction A change that alters the chemical composition of a substance.

Combination Reaction One in which at least two reactants combine to form just one product: A + B ? AB.

Combustion Reaction The reaction of a substance with oxygen to form an oxide, along with heat and light in the form of fire.

Carbohydrates Organic compounds that contain multiple hydroxyl groups in their molecular structure. A basic component of living matter.

Carboxylic Acids A class of organic compounds characterized by the presence of a carboxyl group; general formula, RCOOH.

Carcinogen A cancer-causing agent.

Cfcs Chlorofluorocarbons, which were used in air conditioners, refrigerators, heat pumps, and so forth, and which helped deplete the ozone layer.

Condensation Polymers Large molecules constructed from smaller molecules that have two or more reactive groups. Each small molecule attaches to two others by ester or amide linkages.

Constitutional (Structural) Isomers Compounds that have the same molecular formula but differ in structural formula.

Cycloalkanes Hydrocarbons that have the general molecular formula CnH2n and possess rings of carbon atoms, each carbon atom being bonded to a total of four carbon or hydrogen atoms.

Cartesian Coordinate System A two-dimensional coordinate system in which two number lines are drawn perpendicular to each other, and the origin is assigned at the point of intersection. A third dimension may be taken in the Z direction.

Coordinated Universal Time (Utc) The international time standard based on time kept by atomic clocks.

Condensation Theory A process of solar system formation in which interstellar dust grains act as condensation nuclei.

Conjunction When two planets are lined up with respect to the Sun.

Comet A small mass of ice and dust that revolves around the Sun in a highly elliptical orbit.

Crater (Lunar) A circular depression on the surface of the Moon caused by the impact of a meteorite.

Crescent Moon The Moon viewed when less than one-half of the illuminated surface is observed from the Earth.

Celestial Prime Meridian An imaginary half-circle running from the north celestial pole to the south celestial pole and crossing perpendicular to the celestial equator at the point of the vernal equinox.

Celestial Sphere The apparent sphere of the sky on which all the stars seem to appear.

Cosmic Microwave Background The microwave radiation that fills all space and is believed to be the redshifted glow from the Big Bang.

Cosmological Redshift The shift toward longer wavelengths caused by the expansion of the universe.

Cosmology The study of the structure and evolution of the universe.

Cloud A buoyant mass of visible droplets of water and ice crystals in the lower troposphere.

Convection Cycle The cyclic movement of matter (such as air) as a result of localized heating and convectional heat transfer.

Coriolis Force A pseudoforce arising in an accelerated reference frame on the rotating (accelerating) Earth. Projectiles are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, as observed in the direction of motion.

Cfcs Chlorofluorocarbons, which were used in air conditioners, refrigerators, heat pumps, and so forth, and which helped deplete the ozone layer.

Climate The long-term average weather conditions of a region of the world.

Coalescence The combining of small droplets of water vapor to make larger drops.

Continental Drift The theory that continents move, drifting apart or together.

Convergent Boundary A region where moving plates of the lithosphere are driven together, causing one of the plates to be consumed into the mantle as it descends beneath an overriding plate.

Crust The thin outer layer of the Earth.

Caldera A roughly circular, steep-walled depression formed as a result of the collapse of a volcanic chamber.

Cleavage The splitting of a mineral along an internal molecular plane.

Contact Metamorphism A change in rock brought about primarily by heat rather than pressure.

Continental Shelf The moderately sloping, submerged margin of a continental landmass.

Continental Slope The seaward slope beyond the continental shelf. It extends downward to the ocean basin.

Creep A type of slow mass wasting that involves the particle-by-particle movement of weathered debris down a slope, which takes place year after year.

Cambrian Explosion The great proliferation of life forms that followed the extinction event at the beginning of the Paleozoic era.

Carbon-14 Dating A procedure used to establish the age of ancient organic remains by measuring the concentration of 14C and comparing it to that of present-day organic remains.

Cast Fossil formed when new mineral material fills a mold and hardens.

Correlation Establishing the equivalence of rocks in separate regions; correlation by fossils is an example.

Cross-Cutting Relationships, Principle Of A rock or fault is younger than any rock or fault through which it cuts.






Density A measure of the compactness of matter using a ratio of mass to volume; ? = m/V.

Derived Units Combinations of fundamental units.

Displacement The directional straight-line distance between two points.

Distance The actual path length between two points.

Decibel (Db) A unit of sound intensity level; 0.1 bel.

Doppler Effect An apparent change in frequency resulting from the relative motion of the source and the observer.

Diffraction The bending of waves when moving past an opening or obstacle that has a size smaller than or equal to the wavelength.

Dispersion Different frequencies of light refracted at slightly different angles, giving rise to a spectrum.

Direct Current (Dc) Electric current in which the electrons flow directionally from the negative (-) terminal toward the positive (+) terminal.

Dual Nature of Light Light sometimes behaves as waves and sometimes as particles.

Definite Proportions, Law Of Different samples of a pure compound always contain the same elements in the same proportion by mass.

Decomposition Reaction One in which only one reactant is present and breaks into two (or more) products: AB ? A + B.

Double-Replacement Reactions Reactions that take the form AB + CD ? AD + CB. The positive and negative components of the two compounds ?change partners.?

Daylight Saving Time (Dst) Time advanced one hour from standard time, adopted during the spring and summer months to take advantage of longer evening daylight hours and save electricity.

Dwarf Planet A new class of planets, of which there are three: Pluto, Ceres, and Eris.

Dark Energy A mysterious energy that seems to be causing the expansion of the universe to accelerate.

Dark Matter The as-yet-unidentified nonluminous matter in the universe.

Declination The angular measure in degrees north or south of the celestial equator.

Dew Point The temperature at which a sample of air becomes saturated?that is, has a relative humidity of 100%.

Doppler Radar Radar that uses the Doppler effect on water droplets in clouds to measure the wind speed and direction.

Divergent Boundary A region where plates of the lithosphere are moving away from one another.

Delta The accumulation of sediment formed where running water enters a large body of water such as a lake or ocean.

Desert An area on the Earth?s surface that has a severe lack of precipitation.






Experiment An observation of natural phenomena carried out in a controlled manner so that the results can be duplicated.

Energy The capacity to do work.

Entropy A measure of the disorder of a system.

Electromagnetic Wave A transverse wave consisting of oscillating electric and magnetic fields.

Electric Charge A fundamental property of matter that can be either positive or negative and gives rise to electric forces.

Electric Potential Energy The potential energy that results from work done in separating electric charges.

Electric Power The expenditure of electrical work divided by time; P = W/t = IV.

Electromagnetism The interaction of electrical and magnetic effects.

Electrons Negatively charged subatomic particles.

Electrons Negatively charged subatomic particles.

Excited States The energy levels above the ground state in an atom. See ground state.

Electrons Negatively charged subatomic particles.

Element A substance in which all the atoms have the same number of protons?that is, the same atomic number, Z.

Electron Configuration The order of electrons in the energy levels of an atom.

Element A substance in which all the atoms have the same number of protons?that is, the same atomic number, Z.

Electronegativity A measure of the ability of an atom to attract shared electrons to itself.

Excess Reactant A starting material that is only partially used up in a chemical reaction.

Endothermic Reaction A reaction that absorbs energy from the surroundings.

Equilibrium In chemistry, a dynamic process in which the reactants are combining to form the products at the same rate at which the products are combining to form the reactants.

Exothermic Reaction A reaction that has a net release of energy to the surroundings.

Ester An organic compound that has the general formula RCOOR´.

Elliptical Orbits, Law of (Kepler?S First Law) All planets, asteroids, and comets revolve around the Sun in elliptical orbits.

Equal Areas, Law of (Kepler?S Second Law) As a planet (or asteroid or comet) revolves around the Sun, an imaginary line joining the planet to the Sun sweeps out equal areas in equal periods of time.

Eclipse An occurrence in which one celestial object is partially or totally blocked from view by another.

Ecliptic The apparent annual path of the Sun on the celestial sphere.

Earthquake The release or transfer of energy because of sudden movement resulting from stresses in the Earth?s lithosphere.

Epicenter The point on the surface of the Earth directly above the focus of an earthquake.

Erosion The downslope movement of surface and near-surface materials as a result of gravity and the agents that cause such movements.

Eon The largest unit of geologic time. Eons are divided into eras.

Epoch An interval of geologic time that is a subdivision of a period.

Era An interval of geologic time that is a subdivision of an eon and is made up of periods and epochs.






Free Fall A state of motion solely under the influence of gravity.

Force Any quantity capable of producing motion.

Friction The ever-present resistance to relative motion that occurs whenever two materials are in contact with each other ? solids, liquids, or gases.

Foot-Pound (Ft·Lb) The unit of work (and energy) in the British system.

Fahrenheit Scale A temperature scale with 32°F as the ice point and 212°F as the steam point.

Frequency The number of oscillations of a wave during one second.

Focal Length The distance from the vertex of a mirror or lens to the focal point.

Ferromagnetic Characteristic of substances such as iron, nickel, and cobalt that exhibit the ability to acquire high magnetization.

Fluorescence The property of a substance, such as the mineral fluorite, of producing visible light while it is being acted upon by ultraviolet light.

Fission A process in which a large nucleus is split into two intermediate-size nuclei, with the emission of neutrons and the conversion of mass into energy.

Fusion A process in which smaller nuclei are fused (joined) to form larger ones, with the release of energy.

Formula Mass The sum of the atomic masses of the atoms showing in the chemical formula of the compound or element.

Fats Esters composed of the trialcohol named glycerol, C3H5(OH)3, and long-chain carboxylic acids known as fatty acids.

Functional Group Any atom, group of atoms, or organization of bonds that determines specific properties of a molecule.

Foucault Pendulum A pendulum that is used to demonstrate the rotation of the Earth.

Fault A break or fracture in the surface of a planet or moon along which movement has occurred.

First-Quarter Moon The Moon when it is exactly 90° east of the Sun and appears as a quarter moon on the observer?s meridian at 6 P.M. local solar time.

Full Moon The phase of the Moon that occurs when the Moon is 180° east of the Sun and appears on the observer?s meridian at 12 midnight local solar time.

Front The boundary between two air masses.

Fault A break or fracture in the surface of a planet or moon along which movement has occurred.

Fault-Block Mountain Mountains that were built by normal faulting, in which giant pieces of the Earth?s crust were uplifted.

Focus (Earthquake) The point within the Earth at which the initial energy release of an earthquake occurs.

Fold A buckling of rock layers into arches (anticlines) and troughs (synclines) as a result of compressional forces.

Fold Mountains Mountains characterized by folded rock strata, with external evidence of faulting and central evidence of igneous and metamorphic activity. Fold mountains are believed to be formed at convergent plate boundaries.

Foliation The mineral orientation characteristic of some metamorphic rocks that results from directional pressures during transformation.

Flood Plain The land next to a river or stream that can become inundated when the river or stream overflows.

Fossil A remnant or trace of an organism preserved from prehistoric times.






G The universal gravitational constant; G = 6.67 × 10-11 N·m2/kg2.

Gravitational Potential Energy The potential energy resulting from an object?s position in a gravitational field?in other words, the stored energy that comes from doing work against gravity.

Gas Matter that has no definite volume or shape.

Generator A device that converts mechanical work or energy into electrical energy.

Ground State The lowest energy level of an atom.

Gamma Decay An event in which a nucleus emits a gamma ray and becomes a less energetic form of the same nucleus.

Genetic Effects Defects in the subsequent offspring of recipients of radiation.

Groups The vertical columns in the periodic table.

Great Circle Any circle on the surface of a sphere whose center is at the center of the sphere. Applies especially to imaginary circles on the Earth?s surface that pass through both the North Pole and the South Pole.

Greenwich (Prime) Meridian The reference meridian of longitude, which passes through the old Royal Greenwich Observatory near London.

Greenwich Mean Time (Gmt) The time at the Greenwich or prime (0°) meridian.

Gregorian Calendar The reformed Julian calendar?our present-day calendar.

Geocentric Model The old false theory of the solar system, which placed the Earth at its center.

Gibbous Moon The Moon viewed when more than one-half of its illuminated surface is observed from the Earth.

Galaxy A large-scale aggregate of stars (plus some gas and dust) held together by gravity. Galaxies have a spiral, elliptical, or irregular structure. Each contains, on average, 100 billion solar masses.

Globular Cluster A large, spherical group of gravitationally bound stars, usually found in the outlying regions of a galaxy.

Greenhouse Effect The heat-retaining process of atmospheric gases, such as water vapor and CO2, that results from the selective absorption of long-wavelength terrestrial radiation.

Geology The study of the planet Earth?its dynamics, composition, structure, and history. Also, the study of the chemical and physical properties of other solar system bodies.

Glacial Drift General term for solid material transported and deposited by a glacier.

Glacier A large ice mass that consists of recrystallized snow and that flows on a land surface under the influence of gravity.

Groundwater Water that soaks into the soil.

Geologic Time The time span that covers the long history of the Earth.

Geologic Time Scale A relative time scale based on the fossil contents of rock strata and the principles of superposition and cross-cutting relationships.

Great Dying The most devastating extinction known to geologists; it marked the beginning of the Mesozoic era.






Hypothesis A very tentative explanation of some regularity in nature, or a very tentative answer of any kind.

Horsepower (Hp) A unit of power equal to 550 ft·lb/s.

Heat A form of energy; energy in transit from one body to another as a result of a temperature difference.

Heat Engine A device that uses heat energy to perform useful work.

Heat Pump A device used to transfer heat from a low-temperature reservoir to a high-temperature reservoir.

Hertz (Hz) One cycle per second. The SI unit of frequency.

Heisenberg?S Uncertainty Principle It is impossible to know simultaneously the exact velocity and position of a particle.

Half-Life The time it takes for half the nuclei in a sample of a given radionuclide to decay.

Halogens The elements in Group 7A of the periodic table (F, Cl, Br, I, At).

Hydrogen Bond The dipole-dipole force between a hydrogen atom in one molecule and a nearby oxygen, nitrogen, or fluorine atom in the same or a neighboring molecule.

Hydrocarbons Organic compounds that contain only carbon and hydrogen.

Harmonic Law (Kepler?S Third Law) The square of the sidereal period of a planet is proportional to the cube of its semimajor axis (one-half the major axis).

Heliocentric Model The model of the solar system that places the Sun at its center.

H-R Diagram A plot of the absolute magnitude versus the temperature of stars.

Hubble?S Law The recessional speed of a distant galaxy is directly proportional to its distance away.

Humidity A measure of the water vapor in the air.

Hurricane A tropical storm with winds of 74 mi/h or greater.

Hurricane Warning An alert that hurricane conditions are expected within 24 hours.

Hurricane Watch An advisory alert that hurricane conditions are a definite possibility.

Hydrothermal Metamorphism The chemical alteration of preexisting rocks by chemically reactive, hot-water solutions, which dissolve some ions from the original minerals and replace them with other ions, thus changing the mineral composition of the rock.

Hydrologic Cycle The cyclic movement of the Earth?s water supply from the oceans to the mountains and back again to the oceans.






Instantaneous Speed How fast an object is traveling at a particular moment or instant.

Instantaneous Velocity The velocity at a particular instant of time.

Inertia The natural tendency of an object to remain in a state of rest or in uniform motion in a straight line.

Ideal Gas Law Relates the pressure, volume, and absolute temperature of a gas; p1V1/T1 = p2V2/T2.

Intensity (of Sound Wave) The rate of energy transfer through a given area, with units of watts per square meter (W/m2).

Index of Refraction The ratio of the speed of light in a vacuum to the speed of light in a medium.

Interference, Constructive A superposition of waves for which the combined waveform has a greater amplitude.

Interference, Destructive A superposition of waves for which the combined waveform has a smaller amplitude.

Isotopes Forms of atoms of an element that have the same numbers of protons but differ in their numbers of neutrons.

Inner Transition Elements The lanthanides and actinides, the two rows at the bottom of the periodic table, make up the inner transition elements.

Ion An atom, or chemical combination of atoms, that has a net electric charge.

Ionization Energy The amount of energy it takes to remove an electron from an atom.

Ionic Bonds Electrical forces that hold the ions together in the crystal lattice of an ionic compound.

Ionic Compounds Compounds formed by an electron transfer process in which one or more atoms lose electrons and one or more other atoms gain them to form ions.

International Date Line (Idl) The meridian that is 180° E or W of the prime meridian.

Interplanetary Dust Very small solid particles known as micrometeoroids that exist in the space between the planets.

Insolation The solar radiation received by the Earth and its atmosphere; incoming solar radiation.

Ionosphere The region of the atmosphere between about 70 km (43 mi) and several hundred kilometers in altitude. It is characterized by a high concentration of ions.

Isobar A line on a weather map denoting locations with the same atmospheric pressure.

Ice Storm A storm with accumulations of ice as a result of the surface temperature being below the freezing point.

Inner Core The innermost region of the Earth, which is solid and probably composed of about 85% iron and 15% nickel.

Isostasy The concept that the Earth?s crustal material ?floats? in gravitational equilibrium on a ?fluid? substratum.

Igneous Rock Rock formed by the cooling and solidification of hot, molten material.

Index Fossil A fossil that is related to a specific span of geologic time.






Joule (J) A unit of energy equivalent to 1 N·m or 1 kg·m2/s2.

Jovian Planets The four outer planets?Saturn, Jupiter, Uranus, and Neptune. All have characteristics resembling those of Jupiter.

Jet Streams Rapidly moving ?rivers? of air in the upper troposphere.






Kilo- Metric prefix that means 103, or one thousand.

Kilogram (Kg) The unit of mass in the mks system; 1 kilogram has an equivalent weight of 2.2 pounds.

Kilowatt-Hour (Kwh) A unit of energy (power × time); P = E/t, and E = Pt.

Kinetic Energy Energy of motion equal to 1/2mv2.

Kelvin (K) The unit of temperature on the Kelvin (absolute) temperature scale. A kelvin is equal in magnitude to a degree Celsius.

Kelvin Scale The ?absolute? temperature scale that takes absolute zero as 0 K.

Kilocalorie (Kcal) The amount of heat necessary to raise one kilogram of water one degree Celsius at normal atmospheric pressure.

Kinetic Theory A gas consists of molecules moving independently in all directions at high speeds (the higher the temperature, the higher the average speed), colliding with each other and the walls of the container, and having a distance between molecules that is large, on average, compared with the size of the molecules themselves.

Kuiper Belt A doughnut-shaped ring of space around the Sun beyond Pluto containing many frozen comets.

K-T Event The extinction episode that marks the transition from the Cretaceous period (K) to the Tertiary period (T).






Law A concise statement, in words or a mathematical equation, about a fundamental relationship or regularity of nature.

Length The measurement of space in any direction.

Liter (L) A metric unit of volume or capacity; 1 L = 1000 cm3.

Linear Momentum The product of an object?s mass and its velocity.

Latent Heat The heat associated with a phase change.

Latent Heat of Fusion The amount of heat required to change one kilogram of a substance from the solid to the liquid phase at the melting-point temperature.

Latent Heat of Vaporization The amount of heat required to change one kilogram of a substance from the liquid to the gas phase at the boiling-point temperature.

Liquid Matter that has a definite volume but no definite shape.

Longitudinal Wave A wave in which the particle motion and the wave velocity are parallel to each other.

Linearly Polarized Light The condition of transverse light waves that vibrate in only one plane.

Laser An acronym for light amplification by stimulated emission of radiation; it is coherent, monochromatic light.

Line Absorption Spectrum A set of dark spectral lines of certain frequencies or wavelengths, formed by dispersion of light that has come from an incandescent source and has then passed through a sample of cool gas.

Line Emission Spectrum A set of bright spectral lines of certain frequencies or wavelengths formed by dispersion of light from a gas discharge tube. Each element gives a different set of lines.

Lewis Structures ?Electron dot? symbols used to show valence electrons in molecules and ions of compounds.

Lewis Symbol The element?s symbol represents the nucleus and inner electrons of an atom, and the valence electrons are shown as dots arranged around the symbol.

Limiting Reactant A starting material that is used up completely in a chemical reaction.

Latitude The angular measurement in degrees north or south of the equator for a point on the surface of the Earth.

Longitude The angular measurement in degrees east or west of the prime meridian for a point on the surface of the Earth.

Last-Quarter Moon The phase that occurs when the Moon is 270° east of the Sun and appears on the observer?s meridian at 6 A.M. local solar time.

Lunar Eclipse An eclipse of the Moon caused by the Earth?s blocking the Sun?s rays to the Moon.

Light-Year The distance light travels in one year in vacuum, 9.46 x 1012 km (5.87 x 1012 mi).

Local Group The cluster of galaxies that includes our own Milky Way.

Land Breeze A local wind from land to sea resulting from a convection cycle.

Lapse Rate The rate of temperature decrease with increasing altitude. In the troposphere, the normal lapse rate is -6.5 C°/km, or -3.5 F°/1000 ft.

Lightning An electric discharge in the atmosphere.

Lithosphere The outermost solid portion of the Earth, which includes the crust and part of the upper mantle.

Lava Magma that reaches the Earth?s surface through a volcanic vent.

Lithification The process of forming sedimentary rock from sediment; also called consolidation.

Luster The appearance of a mineral?s surface in reflected light.

Long-Shore Current A current along a shore that results from waves that break at an angle to the shoreline.






Mass A quantity of matter and a measure of the amount of inertia that an object possesses.

Measurement A quantitative observation, one involving numbers.

Mega- Prefix that means 106, or one million.

Meter (M) The standard unit of length in the mks system. It is equal to 39.37 inches, or 3.28 feet.

Metric System The decimal (base-10) system of units employed predominantly throughout the world.

Milli- The metric prefix that means 10-3, or 1 one-thousandth.

Mks System The metric system that has the meter, kilogram, second, and coulomb as the standard units of length, mass, time, and electric charge, respectively.

Motion The changing of position.

Mass A quantity of matter and a measure of the amount of inertia that an object possesses.

Magnetic Declination The angular variation of a compass from geographic north.

Magnetic Domains Local regions of alignment of the magnetic fields of numerous atoms in ferromagnetic materials.

Magnetic Field A set of imaginary lines that indicate the direction in which a small compass needle would point if it were placed at a particular spot.

Motor A device that converts electrical energy into mechanical energy.

Matter (De Broglie) Waves The waves produced by moving particles.

Mass Defect Any decrease in mass during a nuclear reaction.

Mass Number The number of protons plus the number of neutrons in a nucleus; the total number of nucleons.

Metal An element whose atoms tend to lose valence electrons during chemical reactions.

Mixture A type of matter composed of varying proportions of two or more substances that are just physically mixed, not chemically combined.

Molecule An electrically neutral particle composed of two or more atoms chemically combined.

Molarity (M) A measure of solution concentration in terms of moles of solute per liter of solution.

Mole (Mol) The quantity of a substance that contains 6.02 × 1023 formula units (the number of atoms in exactly 12 g of carbon-12).

Monomer A fundamental repeating unit of a polymer.

Meridians Imaginary lines along the surface of the Earth running from the geographic North Pole, perpendicular to the equator, to the geographic South Pole.

Meteor A metallic or stony object that burns up as it passes through the Earth?s atmosphere and appears to be a ?shooting star.?

Meteorite A metallic or stony object from the solar system that strikes the Earth?s surface.

Meteoroids Small, interplanetary objects in space before they encounter the Earth.

Mountain Range A geologic unit or series of mountains.

Magnitude (Absolute) The apparent magnitude that a star would have if it were placed 10 parsecs from the Earth.

Magnitude (Apparent) A measure of the brightness of a star as observed from the Earth.

Main Sequence The narrow band on the H-R diagram on which most stars fall.

Mesosphere The region of the Earth?s atmosphere that lies between approximately 50 and 80 km (30 and 50 mi) in altitude.

Meteorology The study of the lower atmosphere.

Mantle The interior region of the Earth between the core and the crust.

Mid-Ocean Ridge A series of mountain ranges on the ocean floor, more than 84,000 km (52,000 mi) in length, extending through the North and South Atlantic, the Indian Ocean, and the South Pacific.

Moho (Mohorovicic Discontinuity) The boundary between the Earth?s crust and mantle.

Magma Hot, molten, underground rock material.

Metamorphic Rock Rock that results from a change in preexisting rock due to high pressure or temperature or both.

Metamorphism The process by which the structure and mineral content of a rock are changed while the rock remains solid.

Mineral Any naturally occurring inorganic crystalline substance (element or compound) that possesses a fairly definite chemical composition and a distinctive set of physical properties.

Mohs Scale A list of 10 minerals used to measure the hardness of other minerals.

Mass Wasting The downslope movement of overburden under the influence of gravity.

Meander The looping, ribbon-like path of a river channel that results from accumulated deposits of eroded material having diverted the stream flow.

Moraine A ridge of glacial drift.

Mold A hollow depression formed when an embedded shell or bone is dissolved out of a rock.






Newton (N) The unit of force in the mks system; 1 kg·m/s2.

Newton?S First Law of Motion An object will move at a constant velocity unless acted upon by an external unbalanced force.

Newton?S Law of Universal Gravitation The gravitational force between two masses, m1 and m2, is directly proportional to the product of the masses and inversely proportional to the square of the distance r between their centers of mass; F = Gm1m2/r2.

Newton?S Second Law of Motion The acceleration of an object is equal to the net force on the object divided by the mass of the object; a = F/m.

Newton?S Third Law of Motion Whenever one mass exerts a force upon a second mass, the second mass exerts an equal and opposite force upon the first mass.

Neutron Number N, the number of neutrons in the nucleus of an atom.

Neutrons Neutral particles found in the nuclei of atoms.

Nucleons A collective term for neutrons and protons (particles in the nucleus).

Nucleus The central core of an atom; composed of protons and neutrons.

Nuclide A specific type of nucleus, characterized by a specified atomic number and mass number.

Noble Gases The elements of Group 8A of the periodic table (He, Ne, Ar, Kr, Xe, Rn).

Nonmetal An element whose atoms tend to gain (or share) valence electrons during chemical reactions.

Neap Tides Moderate tides with the least variation between high and low. They occur at the first- and last-quarter moons.

New Moon The phase of the Moon that occurs when the Moon is on the same meridian as the Sun at 12 noon local solar time.

Nebulae Vast clouds of interstellar gas and dust.

Neutron Star An extremely high-density star composed almost entirely of neutrons.

Nova A white dwarf star that suddenly increases dramatically in brightness for a brief period of time.

Nucleosynthesis The creation of the nuclei of elements inside stars.

Nitrogen Oxides (Nox) Chemical combinations of nitrogen and oxygen, such as NO and NO2.






Ohm (O) The unit of resistance; equal to one volt per ampere.

Ohm?S Law The voltage across two points is equal to the current flowing between the points times the resistance between the points; V = IR.

Octet Rule In forming compounds, atoms tend to gain, lose, or share electrons to achieve electron configurations of the noble gases.

Oxidation Occurs when oxygen combines with another substance (or when an atom or ion loses electrons).

Organic Chemistry The study of compounds that contain carbon.

Opposition The time at which a planet is on the opposite side of the Earth from the Sun.

Oort Cloud The cloud of cometary objects believed to be orbiting the Sun at 50,000 astronomical units and from which comets originate.

Ozone O3, a form of oxygen found naturally in the atmosphere in the ozonosphere. It is also a constituent of photochemical smog.

Ozonosphere A region of the atmosphere, between approximately 15 and 50 km (9 and 31 mi) in altitude, characterized by ozone concentration.

Ozone O3, a form of oxygen found naturally in the atmosphere in the ozonosphere. It is also a constituent of photochemical smog.

Outer Core Part of the innermost region of the Earth, which is composed of two parts: a solid inner core and a molten, highly viscous outer core.

Original Horizontality, Principle Of The principle that sediments and lava flows are deposited as horizontal layers.






Powers-Of-10 Notation Notation in which numbers are expressed by a coefficient and a power of 10; for example, 2500 = 2.5 × 103. Also called scientific notation.

Physics The most fundamental physical science, concerned with the basic principles and concepts that describe the workings of the universe.

Position The location of an object with respect to another object.

Projectile Motion The motion of a projected or thrown object under the influence of gravity.

Potential Energy The energy a body possesses because of its position in a force field.

Power Work or energy per unit time.

Phases of Matter The physical forms of matter?most commonly, solid, liquid, and gas.

Pressure The force per unit area; p = F/A.

Period In physics, the time for a complete cycle of motion. In chemistry, one of the seven horizontal rows of the periodic table. In geology, an interval of geologic time that is a subdivision of an era and is made up of epochs.

Polarization The preferential orientation of the electric vector of a light wave to one plane.

Parallel Circuit A circuit in which an entering current divides proportionately among the circuit elements.

Poles, Law of (Magnetic) Like poles repel, and unlike poles attract.

Protons Positively charged particles in the nuclei of atoms.

Phosphorescence A glow of light that persists after the removal of the source of photons needed for excitation of the material?s electrons.

Photoelectric Effect The emission of electrons that occurs when certain metals are exposed to light.

Photon A ?particle? of electromagnetic energy.

Principal Quantum Number "The numbers n = 1, 2, 3,? used to designate the various principal energy levels that an electron may occupy in an atom."

Plasma A high-temperature gas of electrons and protons or other nuclei.

Protons Positively charged particles in the nuclei of atoms.

Period In physics, the time for a complete cycle of motion. In chemistry, one of the seven horizontal rows of the periodic table. In geology, an interval of geologic time that is a subdivision of an era and is made up of epochs.

Periodic Law The properties of elements are periodic functions of their atomic numbers

Polar Covalent Bond One in which the pair of bonding electrons is unequally shared, leading to the bond?s having a slightly positive end and a slightly negative end.

Polar Molecule A molecule that has a positive end and a negative end?that is, one that has a dipole.

Ph A measure (on a logarithmic scale) of the hydrogen ion (or hydronium ion) concentration in a solution.

Precipitate An insoluble solid that appears when two clear liquids (usually aqueous solutions) are mixed.

Products The substances formed during a chemical reaction.

Polymer A compound of very high molecular mass whose chainlike molecules are made up of repeating units called monomers.

Proteins Long-chain polyamides formed by the enzyme-catalyzed condensation of amino acids.

Parallels Imaginary lines encircling the Earth parallel to the plane of the equator.

Parsec (Pc) The distance to a star when the star exhibits a parallax of one second of arc. This distance is equal to 3.26 light-years or 206,265 astronomical units.

Post Meridiem Pertaining to time from 12 noon to 12 midnight.

Precession The slow rotation of the axis of spin of the Earth around an axis perpendicular to the ecliptic plane. The rotation is clockwise as observed from the north celestial pole.

Parallax The apparent motion, or shift, that occurs between two fixed objects when the observer changes position.

Prograde Motion Orbital or rotational motion in the forward direction. In the solar system, this is west-to-east, or counterclockwise, as viewed from above the Earth?s North Pole.

Partial Lunar Eclipse The Earth?s shadow does not completely cover the Moon.

Partial Lunar Eclipse The Earth?s shadow does not completely cover the Moon.

Partial Solar Eclipse Partial blocking of the Sun, seen by an observer in the penumbra.

Partial Solar Eclipse Partial blocking of the Sun, seen by an observer in the penumbra.

Penumbra A region of partial shadow. During an eclipse, an observer in the penumbra sees only a partial eclipse.

Plains (Lunar) Large, dark, flat areas on the Moon believed to be craters formed by meteorite impact that then filled with volcanic lava.

Parallax The apparent motion, or shift, that occurs between two fixed objects when the observer changes position.

Parsec (Pc) The distance to a star when the star exhibits a parallax of one second of arc. This distance is equal to 3.26 light-years or 206,265 astronomical units.

Photosphere The Sun?s outer surface, visible to the eye.

Planetary Nebula A luminous shell of gas ejected from an old, low-mass star.

Proton-Proton Chain A series of stellar nuclear reactions in which four hydrogen nuclei (protons) combine to form one helium nucleus and release energy.

Photosynthesis The process by which plants convert CO2 and H2O to sugars and oxygen.

Psychrometer An instrument used to measure relative humidity.

Photochemical Smog Air pollution resulting from the photochemical reactions of hydrocarbons with other pollutants and atmospheric oxygen in the presence of sunlight.

Pollution Any atypical contributions to the environment resulting from the activities of humans.

Pangaea The giant supercontinent that is believed to have existed over 200 million years ago.

Plate Tectonics The theory that the Earth?s lithosphere is made up of rigid plates that are in relative motion with respect to each other.

Plutons Intrusive igneous rocks, formed below the surface of the Earth by solidification of magma.

Pyroclastics (Tephra) Solid material emitted by volcanoes; range in size from fine dust to large boulders.

Permafrost Ground that is permanently frozen.

Permeability A material?s capacity to transmit fluids.

Paleontology The systematic study of fossils and prehistoric life forms.

Period In physics, the time for a complete cycle of motion. In chemistry, one of the seven horizontal rows of the periodic table. In geology, an interval of geologic time that is a subdivision of an era and is made up of epochs.






Quantum A discrete amount.

Quantum Mechanics The branch of physics that replaced the classical-mechanical view (that everything moved according to exact laws of nature) with the concept of probability. Schrödinger?s equation forms the basis of quantum wave mechanics.






Renewable Energy Sources Energy sources that cannot be exhausted, such as wind and hydro power.

Radiation The transfer of energy by means of electromagnetic waves.

Redshift A Doppler effect caused when a light source, such as a galaxy, moves away from the observer and shifts the light frequencies lower, or toward the red end of the electromagnetic spectrum.

Resonance A wave effect that occurs when an object has a natural frequency that corresponds to an external frequency.

Ray A straight line that represents the path of light.

Real Image An image from a mirror or lens that can be brought to focus on a screen.

Reflection The change in the direction of a wave when it strikes and rebounds from a surface or the boundary between two media.

Reflection, Diffuse Reflection from a rough surface in which reflected rays are not parallel.

Reflection, Law Of The angle of incidence equals the angle of reflection, ?i = ?r, as measured relative to the normal, a line perpendicular to the reflecting surface.

Reflection, Specular Reflection from a smooth surface in which the reflected rays are parallel.

Reflection, Total Internal A phenomenon in which light is totally reflected in a medium because refraction is impossible.

Refraction The bending of light waves caused by a speed change as light goes from one medium to another.

Resistance (Electrical) The opposition to the flow of electric charge.

Radioactive Isotope An isotope that undergoes spontaneous decay.

Radioactivity The spontaneous process of a sample of a radionuclide undergoing a change by the emission of particles or rays.

Radionuclides Types of nuclei that undergo radioactive decay.

Representative Elements The A group elements in the periodic table.

Reactants The original substances in a chemical reaction.

Reduction Occurs when oxygen is removed from a compound (or when an atom or ion gains electrons).

Retrograde Motion Orbital or rotational motion in the backward direction. In the solar system, this is east to west, or clockwise, as viewed from above the Earth?s North Pole.

Revolution The movement of one mass around another.

Rotation The turning of an object about an axis passing through the mass.

Rays (Lunar) Streaks of light-colored material extending outward from craters on the Moon.

Rill A narrow trench or valley on the Moon.

Red Giant A relatively cool, very bright star that has a diameter much larger than average.

Right Ascension A coordinate for measuring the east-west positions of celestial objects. The angle is measured eastward from the vernal equinox in hours, minutes, and seconds.

Radar An instrument that sends out electromagnetic (radio) waves, monitors the returning waves that are reflected by some object, and thereby locates the object. Radar stands for radio detecting and ranging. Radar is used to detect and monitor precipitation and severe storms.

Rain Gauge An open, calibrated container used to measure amounts of precipitation.

Rayleigh Scattering The preferential scattering of light by air molecules and particles that accounts for the blueness of the sky. The scattering is proportional to 1/?4.

Relative Humidity The ratio of the actual moisture content of a volume of air to its maximum moisture capacity at a given temperature.

Remanent Magnetism The magnetism retained in rocks containing ferrite minerals after these rocks solidify in the Earth?s magnetic field.

Regional Metamorphism A change in rock over a large area, brought about by both heat and pressure.

Rock A solid, cohesive natural aggregate of one or more minerals.

Rock Cycle The cyclic changes of rock, during which the rock is created, destroyed, and metamorphosed by the Earth?s internal and external geologic processes.

Radiometric Dating A general name for dating rocks and organic remains by measuring the rate of decay of radionuclides that the rocks and remains contain.

Relative Geologic Time A time scale obtained when rocks and the geologic events they record are placed in chronologic order without regard to actual dates.

Replacement Fossil Fossil formed when a mineral slowly replaces parts of a buried organism.






Science An organized body of knowledge about the natural universe and the processes by which that knowledge is acquired and tested.

Scientific Attitude An attitude of curiosity, objectivity, and willingness to follow where evidence leads in association with the scientific method.

Scientific Method An investigative process that holds that no concept or model of nature is valid unless the predictions it generates agree with experimental results. That is, all hypotheses should be based on as much relevant data as possible and then should be tested and verified.

Second The standard unit of time. It is now defined in terms of the frequency of a certain transition in the cesium atom.

Si (International System of Units) A modernized version of the metric system that contains seven base units.

Significant Figures A method of estimating or expressing error in mathematical operations and measurements.

Standard Unit A fixed and reproducible reference value used for the purpose of taking accurate measurements.

System of Units A group of standard units and their combinations. The two major systems of units in use today are the metric system and the British system.

Scalar A quantity that has a magnitude but has no direction associated with it.

Solid Matter that has a definite volume and a definite shape.

Specific Heat The amount of heat energy in kilocalories necessary to raise the temperature of one kilogram of the substance one degree Celsius.

Steam Point The temperature at which water boils under one atmosphere of pressure, 100 oC or 212oF.

Sound A wave phenomenon caused by variations in pressure in a medium such as air.

Sound Spectrum An ordered arrangement of various frequencies or wavelengths of sound. The three main regions of the sound spectrum are the infrasonic, the audible, and the ultrasonic.

Speed of Light (C) How fast light travels. In air or a vacuum, c = 3.00×108 m/s, or 186,000 mi/s.

Speed of Sound How fast sound travels in a medium; for example, vs = 344 m/s in air at room temperature.

Standing Wave A ?stationary? waveform arising from the interference of waves traveling in opposite directions.

Superposition, Principle of (Wave) The combined waveform of two or more interfering waves is given by the sum of the displacements of the individual waves.

Series Circuit A circuit in which an entering current flows individually through all the circuit elements.

Stimulated Emission Process in which an excited atom is caused to emit a photon.

Somatic Effects Short-term and long-term effects on the health of a recipient of radiation.

Strong Nuclear Force The short-range force of attraction that acts between two nucleons and holds the nucleus together.

Saturated Solution A solution that has the maximum amount of solute dissolved in the solvent at a given temperature.

Solubility The amount of solute that will dissolve in a specified volume or mass of solvent (at a given temperature) to produce a saturated solution.

Solution A mixture that is uniform throughout. Also called a homogeneous mixture.

Supersaturated Solution A solution that contains more than the normal maximum amount of dissolved solute at a given temperature and hence is unstable.

Stock System A system of nomenclature for compounds of metals that form more than one ion. A Roman numeral placed in parentheses directly after the name of the metal denotes its ionic charge in the compound being named.

Salt An ionic compound that contains any cation except H+ combined with any anion except OH-.

Single-Replacement Reactions Reactions in which one element replaces another that is in a compound: A + BC ? B + AC.

Structural Formula A graphical representation of the way the atoms are connected to one another in a molecule.

Synthetics Materials whose molecules have no duplicates in nature.

Sidereal Day The rotation period of the Earth with respect to the vernal equinox. One sidereal day is 23 h, 56 min, 4.091 s.

Sidereal Year The time interval for the Earth to make one complete revolution around the Sun with respect to any particular star other than the Sun.

Solar Day The time elapsed between two successive crossings of the same meridian by the Sun.

Standard Time Zones The division of the surface of the Earth into 24 time zones, each containing about 15° of longitude.

Summer Solstice The farthest point of the Sun?s latitude north of the equator (for the Northern Hemisphere), around June 21. The beginning of summer.

Sidereal Period The orbital or rotational period of any object with respect to the stars.

Solar Nebula A large, swirling volume of interstellar cold gas and dust that contracted under the influence of its own gravity and formed in the shape of a flattened rotating disk.

Solar System The Sun, nine planets and their satellites, the asteroids, comets, meteoroids, and interplanetary dust.

Sidereal Month The time it takes for the Moon to make one complete cycle relative to stars, 27.3 days.

Solar Eclipse An eclipse of the Sun caused by the Moon blocking the Sun?s rays to an observer on the Earth.

Spring Tides The tides of greatest variation between high and low.

Synodic Month The time it takes the Moon to go through one complete cycle of phases (a month of phases), 29.5 days.

Supernova An exploding star.

Sea Breeze A local wind blowing from the sea to land as a result of a convection cycle.

Stratosphere The region of the Earth?s atmosphere approximately 16 to 50 km (10 to 30 mi) in altitude.

Smog A contraction of smoke-fog, used to describe the combination of these conditions.

Snowstorm An appreciable accumulation of snow. When accompanied by high winds and low temperatures, it is referred to as a blizzard.

Source Region The region or surface from which an air mass derives its physical characteristics.

Storm Surge The great dome of water associated with a hurricane when it makes landfall.

Sulfur Dioxide (So2) An atmospheric pollutant formed by the oxidation of sulfur; it contributes to acid rain.

Seafloor Spreading The theory that the seafloor slowly spreads and moves away from mid-ocean ridges. The spreading is believed to be due to convection cycles of subterranean molten material that cause the formation of the ridges and a surface motion in a lateral direction from the ridges.

Seismic Waves The waves generated by the energy release of an earthquake.

Subduction The process in which one plate is deflected downward beneath another plate into the asthenosphere.

Sedimentary Rock Rock formed from the lithification, or consolidation, of layers of sediment.

Sediments Mineral or organic matter deposited by water, air, or ice.

Shear Metamorphism A change in rock brought about primarily by pressure rather than heat.

Silicate Any one of numerous minerals that have the oxygen and silicon tetrahedron as their basic structure.

Streak The color of a powdered mineral on a streak plate (unglazed porcelain).

Subduction The process in which one plate is deflected downward beneath another plate into the asthenosphere.

Seamount An isolated submarine volcanic structure.

Sinkhole A depression on the land surface where soluble rock (limestone) has been removed by groundwater.

Stream Any flow of water occurring between well-defined banks.

Superposition, Principle of (Geology) The principle that in a succession of stratified deposits, the younger layers lie over the older layers.






Theory A tested explanation of a broad segment of basic natural phenomena.

Time The continuous forward-flowing of events.

Terminal Velocity The maximum velocity reached by a falling object because of air resistance.

Torque A force that tends to produce rotational motion.

Temperature A measure of the average kinetic energy of the molecules in a sample.

Thermodynamics The science dealing with the production of heat, the flow of heat, and the conversion of heat to work.

Thermodynamics, First Law Of The heat energy added to a system must go into increasing the internal energy of the system, or any work done by the system, or both. The law, which is based on the conservation of energy, also states that heat energy removed from a system must produce a decrease in the internal energy of the system, or any work done on the system, or both.

Thermodynamics, Second Law Of It is impossible for heat to flow spontaneously from an object having a lower temperature to an object having a higher temperature.

Thermodynamics, Third Law Of A temperature of absolute zero can never be attained.

Transverse Wave A wave in which the vibrations are perpendicular to the wave velocity.

Transformer A device that increases or decreases the voltage or alternating current.

Transition Elements The B group of elements in the periodic table.

Tropical Year The time interval from one vernal equinox to the next.

Terrestrial Planets The four inner planets?Mercury, Venus, Earth, and Mars. All are similar to the Earth in general chemical and physical properties.

Tides The periodic rise and fall of the water level along the shores of large bodies of water.

Total Lunar Eclipse The Earth?s shadow completely covers the Moon.

Total Lunar Eclipse The Earth?s shadow completely covers the Moon.

Total Solar Eclipse Total blocking of the Sun, seen by an observer in the umbra.

Total Solar Eclipse Total blocking of the Sun, seen by an observer in the umbra.

Thermosphere The region of the Earth?s atmosphere extending from about 80 km (50 mi) in altitude to the outer reaches of the atmosphere.

Troposphere The region of the Earth?s atmosphere from the ground up to about 16 km (10 mi).

Temperature Inversion A condition characterized by an inverted lapse rate.

Thunder The sound associated with lightning; it arises from the explosive release of electrical energy.

Tornado A violent storm characterized by a funnel-shaped cloud and high winds.

Tornado Warning The alert issued when a tornado has actually been sighted or is indicated on radar.

Tornado Watch The alert issued when conditions are favorable for tornado formation.

Transform Boundary A region of the lithosphere where a moving plate slides along one side of another without creating or destroying lithosphere.

Tsunami A Japanese word for a seismic sea wave?an unusually large sea wave produced by a seaquake or undersea volcanic eruption.

Tides The periodic rise and fall of the water level along the shores of large bodies of water.

Trace Fossil Fossil imprint made by the movement of an animal.






Unbalanced (Net) Force The sum of vector forces with a nonzero result. A force capable of producing motion.

Ultrasound Sound with frequency above 20 kHz.

Unsaturated Solution A solution in which more solute can be dissolved at the same temperature.

Umbra A region of total darkness in a shadow. During an eclipse, an observer in the umbra sees a total eclipse.

Universe Everything that is?all energy, matter, and space.

Uniformitarianism The principle that the same processes operate on and within the Earth today as in the past. Hence the present is considered the key to the past.

Unconformity A break in the geologic rock record.






Vector A quantity that has both magnitude and direction.

Virtual Image An image from a lens or mirror that cannot be brought to focus on a screen.

Volt The unit of voltage equal to one joule per coulomb.

Voltage The amount of work it would take to move an electric charge between two points, divided by the value of the charge?that is, work per unit charge.

Valence Electrons The electrons that are involved in bond formation, usually those in an atom?s outer shell.

Valence Shell An atom?s outer shell, which contains the valence electrons.

Vernal Equinox The point where the Sun crosses the celestial equator from south to north, around March 21. The beginning of spring.

Volcanic Mountains Mountains that have been built by volcanic eruptions.

Volcano A hill or mountain formed from lava and rock fragments ejected through a vent in the Earth?s surface.

Viscosity The internal property of a substance that offers resistance to flow.

Volcano A hill or mountain formed from lava and rock fragments ejected through a vent in the Earth?s surface.






Weight A measure of the force due to gravitational attraction (w = mg, on the Earth?s surface).

Watt (W) A unit of power equivalent to 1 kg·m2/s3, or 1 J/s.

Work The product of a force and the parallel distance through which it acts.

Wave The propagation of energy from a disturbance.

Wave Speed The distance a wave travels divided by the time of travel.

Wavelength The distance from any point on a wave to an identical point on the adjacent wave.

Winter Solstice The farthest point of the Sun?s latitude south of the equator (for the Northern Hemisphere), around December 22. The beginning of winter.

Waning Phase The illuminated portion of the Moon is getting smaller as observed from the Earth.

Waxing Phase The illuminated portion of the Moon is getting larger as observed from the Earth.

White Dwarf A hot white star that has a much smaller diameter and much higher density than average. It is believed to be the final stage of a low-mass star.

Weather The atmospheric conditions of the lower troposphere.

Wind The horizontal movement of air; air motion along the Earth?s surface.

Wind Vane A free-rotating device that, because of its shape, lines up with the wind and indicates the wind direction.

Water Table The boundary between the zone of aeration and the zone of saturation.

Weathering The physical disintegration and chemical decomposition of rock.






X-Rays High-frequency, high-energy electromagnetic radiation formed when high-speed electrons strike a metallic target.







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