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A

A - The symbol for ampere. Also, when in lower-case italic, the symbol for acceleration.

aberration- (ab-er-RAY-shun) Distortion in an image produced by a lens.

absolute zero- The temperature at which a substance has no kinetic energy per particle (thermal) to give up. This temperature corresponds to 0 K, or to -273"C.

acceleration- (ak-sel '-er-RAY~shun) The rate at which velocity is changing. The change may be in magnitude, direction, or both.

action force- One of the pair of forces described in Newton's third law.

additive primary colors- Red, blue and green light. These colors when added together produce white light.

adiabatic- (ay-dee-ah-BAT-ik) Term applied to expansion or compression of a gas occurring without gain or loss of heat.

air resistance- Friction, or drag, that acts on some-thing moving through air.

alternating current- (ac) Electric current that repeatedly reverses in direction, twice each cycle. Usually at 60 cycles per second, or hertz (Hz), in North America, or 50 hertz elsewhere.

ampere- (AM-peer) SI unit of electric current. A flow of one coulomb of charge per second is one ampere (symbol A).

amplitude- (AMP- lih-tewd) The distance from the midpoint to the maximum (crest) of a wave or, equivalently, from the midpoint to the minimum (trough).

aneroid barometer- (AN-er- oyd buh-ROM-uh-ter) An instrument used to measure atmospheric pressure; based on the movement of the lid of a metal box.

angle of incidence- (IN-sih-dens) Angle between an incident ray and the normal to a surface

angle of reflection- Angle between a reflected ray and the normal to a surface

angular momentum- (mo-MEN-tum) Product of rota-tional inertia and rotational velocity

antinodes- The positions on a standing wave where the largest amplitudes occur.

apogee- (AP-uh-jee) The point in a satellite's elliptical orbit farthest from the center of the earth.

Archimedes' principle- (ark-uh-MEF-deez) The relationship between buoyancy and displaced fluid: An immersed object is buoyed up by a force equal to the weight of the fluid it displaces.

astigmatism- (uh-STIG-muh-tizm) A defect of the eye caused when the cornea is curved more in one direction than in another.

atom- The smallest particle of an element that can be identified with that element. Consists of protons and neutrons in a nucleus surrounded by electrons.

atomic mass number- Total number of nucleons (neu-trons and protons) in the nucleus of an atom.

atomic number- Number of protons in the nucleus of an atom.

average speed- Path distance divided by time interval.

axis- (AK- sis) (a) The straight line around which an object may rotate or revolve. (b) A horizontal or vertical reference line in a graph.

B

barometer- An instrument used to measure the pressure of the atmosphere.

beats- A throbbing variation in the loudness of sound caused by interference when two tones of slightly different frequencies are sounded together.

Bernoulli's principle- (ber-NOO-leez) The statement that the pressure in a fluid decreases as the speed of the fluid increases.

bimetallic strip- (bi~-meh-TAL'-ik) Two strips of different metals, such as one of brass and one of iron, welded or riveted together into one strip. Because the two substances expand at different rates, when heated or cooled the strip bends. Used in thermostats.

black hole- A mass that has collapsed to so great a density that its enormous local gravitational field prevents light from escaping.

blue shift- An increase in the measured frequency of light from an approaching source; called the blue shift because the apparent increase is toward the high-frequency, or blue, end of the color spectrum. Also occurs when an observer approaches a source.

boiling- The change of phase from liquid to gas that occurs beneath the surface in the liquid. Thegas forms bubbles that rise to the surface and escape.

bow wave- The V-shaped wave produced by an object moving on a liquid surface faster than the wave speed.

Boyle's law- For a constant number of molecules of gas at constant temperature, the product of pressure and volume is constant.

breeder reactor- A nuclear fission reactor that not only produces power but produces more nuclear fuel than it consumes by converting a nonfissionable uranium isotope into a fissionable plutonium isotope.

Brownian motion- Random movement observed among microscopic particles suspended in a fluid medium.

buoyancy- (BOY-un-see) The apparent loss of weight of an object immersed or submerged in a fluid.

buoyant force- (BOY-unt) The net upward force exerted by a fluid on a submerged or immersed object.

C

C- (a) The symbol for coulomb (b) When preceded or followed by the degree symbol °, the symbol for Celsius.

cal- The symbol for calorie.

calorie- (KAL-er-ee) A unit of heat. One calorie (symbol cal) is the heat required to raise the temperature of one gram of water one Celsius degree. One Calorie (with a capital C) is equal to one thousand calo-ries and is the unit used in describing the energy available from food. (1 cal 4.184 J, or 1 J = 0.24 cal)

capacitor- (kuh-PAS-ih-ter) A device used to store charge in a circuit.

Carnot efficiency- (KAR-no) Ideal maximum percent-age of input energy that can be converted to work in a heat engine.

Celsius scale- (SEL-see-us) A temperature scale with 0 the melt-freeze temperature for water and 100 the boil-condense temperature of water at standard pressure (one atmosphere at sea level).

center of gravity- Point at the center of an object's weight distribution, where the force of gravity can be considered to act. Abbreviated CG.

center of mass- Point at the center of an object's mass distribution, where all its mass can be considered to be concentrated. For everyday conditions, it is the same as the center of gravity

centrifugal force- (sen-TRIH-fuh-gul) An apparent outward force on a rotating or revolving body. It is fictitious in the sense that it is not part of an interaction but is due to the tendency of a moving body to move in a straight-line path.

centripetal force- (sen -TRIH-peh-tul) A center-directed force that causes an object to move in a curved (sometimes circular) path.

chain reaction- A self-sustaining reaction in which one reaction event stimulates one or more additional reaction events to keep the process going.

charge- The fundamental electrical property to which the mutual attractions or repulsions between electrons or protons is attributed.

chemical formula- A description that uses numbers and symbols of elements to describe the proportions of elements in a compound or reaction.

circuit- (SER-kit) Any complete path along which charge can flow

coherent- (ko-HEER-ent) As applied to light waves, having identical frequency and identical phase, and traveling in the same direction. Lasers produce coherent light.

complementary colors- (kom -pluh-MENT -uh-ree) Two colors of light beams that when added together appear white.

component- (kom-PO-nent) One of the vectors, often mutually perpendicular, whose sum is a resultant vector. Any resultant vector may be regarded as the combination of two or more components. (See resultant.)

compound- A chemical substance made of atoms of two or more different elements combined in a fixed proportion.

compression- (kom-PRE-shun) (a) In mechanics, the act of squeezing material and reducing its volume. (b) In sound, a pulse of compressed air (or other matter); opposite of rarefaction.

condensation- (kon - - den- SAY' -shun) The change of phase of a gas into a liquid; the opposite of evaporation.

conduction- (a) In heat, energy transfer from particle to particle within certain materials, or from one material to another when the two are in direct con-tact. (b) In electricity, the flow of charge through a conductor.

conductor- (a) Material through which heat can be transferred. (b) Material, usually a metal, through which electric charge can flow. Good conductors of heat are generally good charge conductors.

conservation of charge- The principle that net electric charge is neither created nor destroyed but is transferable from one material to another.

conserved- Term applied to a physical quantity, such as momentum, energy, or electric charge, that remains unchanged during interactions.

constructive interference- Addition of two or more waves when wave crests overlap to produce a resulting wave of increased amplitude.

convection- A means of heat transfer by movement of the heated substance itself such as by currents in a fluid.

converging lens- A lens that is thickest in the middle, causing parallel rays of light to converge to a focus.

cornea- (KOR-nee-uh) The transparent covering over the eyeball.

correspondence principle- If a new theory is valid, it must account for the verified results of the old theory in the region where both theories apply.

coulomb- (KOO-lom) SI unit of charge. One coulomb (symbol C) is equal to the total charge of 6.24EE18 electrons.
Coulomb's law- The relationship among electrical force, charges, and distance: The electrical forcebetween two charges varies directly as the product of the charges and inversely as the square of the distance between them.

crest- One of the places in a wave where the wave is highest or the disturbance is greatest.

critical angle- The minimum angle of incidence for which a light ray is totally reflected within a medium.

critical mass- The minimum mass of fissionable material in a nuclear reactor or nuclear bomb that will sustain a chain reaction.

crystal- (KRIS-tul) A regular geometric shape found in a solid in which the component particles are arranged in an orderly, three-dimensional, repeating pattern.

current- See electric current

D

density - (DEN-sih-tee) A property of a substance, equal to its mass per volume.

destructive interference- Combination of waves where crest parts of one wave overlap trough parts of another, resulting in a wave of decreased ampli-tude.

diode- (DI-od) An electronic device that restricts cur-rent to flow in a single direction in an electric circuit.

diffraction- (dih-FRAK- shun) The bending of a wave around a barrier, such as an obstacle or the edges of an opening.

diffraction grating- A series of closely spaced parallel slits or grooves that are used to separate colors of light by interference.

diffuse reflection- (dih-FYOOS) The reflection of waves in many directions from a rough surface.

direct current- (dc) Electric current whose flow of charge is always in one direction.

dispersion- (dih-SPER-zhun) The separation of light into colors arranged according to their frequency by interaction with a prism or diffraction grating, for example.

displaced- Term applied to the fluid that is moved out of the way when an object is placed in fluid. A submerged object always displaces a volume of fluid equal to its own volume.

diverging lens- A lens that is thinnest in the middle and that causes parallel rays of light to diverge.

Doppler effect- (DOP-ler) The change in frequency of a wave due to the motion of the source or of the receiver.

E

eddy- Changing, curling paths in turbulent flow of a fluid.

efficiency- In a machine, the ratio of useful energy out-put to total energy input, or the percentage of the work input that is converted to work output.

elapsed time- The time that has passed since begin-ning of an event.

elastic- Term applied to a material that returns to its original shape after it has been stretched or compressed.

elastic collision- Collision in which colliding objects rebound without lasting deformation or heat generation.

elasticity- (ih-las-TIH-sih-tee) The property of a solid wherein a change in shape is experienced when a deforming force acts on it, with a return to its original shape when the deforming force is removed.

elastic limit- The distance of stretching or compressing beyond which an elastic material will not return to its original shape.

electric charge- See charge.

electric current- The flow of electric charge; measured in amperes (coulombs per second).

electric field- A force field that fills the space around every electric charge or group of charges. Measured by force per charge (N/C).

electric potential- Electric potential energy per coulomb (I/C) at a location in an electric field; measured in volts and often called voltage.

electric potential- energy Energy a charge has due to its location in an electric field.

electric power- The rate at which electric energy is converted into another form, such as light, heat, or mechanical energy (or converted from another form into electric energy).

electric resistance- The resistance of a material to the flow of electric current through it; measured in ohms.

electrical force- A force that one charge exerts on another. When the charges are the same sign, they repel; when the charges are opposite, they attract.

electrically polarized- Term applied to an atom or molecule in which the charges are aligned so that one side is slightly more positive or negative than the opposite side.

electromagnet- (ih-lek~-tro-MAG~-net) Magnet with afield produced by electric current; usually in the form of a wire coiled around a piece of iron.

electromagnetic induction- (ih-lek'-tro-mag-NET~-ik in-DUK- shun) The phenomenon of inducing a voltage in a conductor by changing the magnetic field near the conductor.

electromagnetic spectrum- The range of electromag-netic waves extending from radio waves to gamma rays.

electromagnetic wave- A wave that is partly electric and partly magnetic and carries energy. Emitted by vibrating electric charges.

electrostatics- (ih-lek'-tro-STAT~-iks) The study of electric charges at rest.

element - A substance made of only one kind of atom. Examples of elements are carbon, hydrogen, oxygen, and nitrogen.

ellipse- (ih-LIPS) An oval-shaped curve that is the path of a point that moves such that the sum of its distances from two fixed points (foci) is constant.

energy- That property of an object or a system which enables it to do work; measured in joules.

entropy- A measure of the amount of disorder in a system.

equilibrium- (ee-kwih-LIH-bree-um) In general, a state of balance. Examples: The state of a body on which no net force acts. The state of a body on which no net torque acts. The state of a liquid in which the processes of evaporation and condensation are taking place at equal rates.

escape speed- The minimum speed necessary for an object to escape permanently from a gravitational field that holds it.

evaporation- (ih-vap'-or-AY'-shun) The change of phase from liquid to gas that takes place at the surface of a liquid.

eyepiece- Lens of a telescope closest to the eye; enlarges the real image formed by the first lens.

F

fact- A close agreement by competent observers of a series of observations of the same phenomena.

Fahrenheit scale- (FA-ren-hit) The temperature scale in common use in the United States. The number 32 is assigned to the freezing point of water, and the number 212 to the boiling point of water (at standard atmospheric pressure).

Faraday's law- (FA-ruh-dayz) Induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within those loops. (37.2) In general, an electric field is induced in any region of space in which a magnetic field is changing with time. The magnitude of the induced electric field is proportional to the rate at which the magnetic field changes.

farsighted- Term applied to a person who has trouble focusing on nearby objects because the eyeball is so short that images form behind the retina.

field- See force field.

first law of thermodynamics- Heat added to a system is transformed to an equal amount of some other form of energy; aversion of the law of energy conservation.

first postulate of special relativity- All the laws of nature are the same in all uniformly moving reference frames.

fission- See nuclear fission.

fluid- Anything that flows; in particular, any liquid or gas.

focal length- The distance between the center of a lens and either focal point.

focal plane- A plane passing through either focal point of a lens that is perpendicular to the principal axis. For a converging lens, any incident parallel beam of light converges to a point somewhere on a focal plane. For a diverging lens, such a beam appears to come from a point on a focal plane.

focal point- For a converging lens, the point at which a beam of light parallel to the principal axis converges. For a diverging lens, the point from which such a beam appears to come.

focus- (FO-kus); p1. foci (FO:si) (a) For an ellipse, one of the two points for which the sum of the distances to any point on the ellipse is a constant. A satellite orbiting the earth moves in an ellipse that has the earth at one focus. (b) For optics, the point where parallel light rays converge.

force- Any influence that tends to accelerate an object; a push or pull; measured in newtons. A vector quantity

forced vibration- The vibration of an object that is made to vibrate by another vibrating object that is nearby. The sounding board in a musical instrument amplifies the sound through forced vibration.

force field- That which exists in the space surround-ing a mass, electric charge, or magnet, so that another mass, electric charge, or magnet introduced to this region will experience a force. Examples of force fields are gravitational fields, electric fields, and magnetic fields.

free fall- Motion under the influence of the gravitational force only.

freezing- Change in phase from liquid to solid.

frequency- (FREF-kwen-see) The number of events (cycles, vibrations, oscillations, or any repeated event) per time; measured in hertz (or events per time). Inverse of period.

friction- The force that acts to resist the relative motion (or attempted motion) of objects or materials that are in contact.

fulcrum- (FOOL-krum) The pivot point of a lever.

fusion- See nuclear fusion.

G H

g- (a) The symbol for gram. (b) when in lower-case italic, the symbol for the acceleration due to gravity (at the earth's surface, 9.8 m/s^2). (c) When in lowercase bold, the gravitational field vector (at the earth's surface, 9.8 N/kg). (d) When in uppercase italic, the symbol for the universal constant of gravitation (6.67 x 10-11 Nm^2/kg^2).

general theory- of relativity Einstein's generalization of special relativity which features a geometric theory of gravitation.

generator- A machine that produces electric current by rotating a coil within a stationary magnetic field.

global warming- See greenhouse effect.

gravitational field- (grav'-ih-TAY'-shun~ul) A force field that exists in the space around every mass or group of masses.

greenhouse effect- The warming effect whose cause is that short-wavelength radiant energy from the sun can enter the atmosphere and be absorbed by the earth more easily than long-wavelength energy from the earth can leave.

grounding- Allowing charges to move freely along a connection between a conductor and the ground.

group- Elements in the same column of the periodic table.

half-life- The time required for half the atoms of a radioactive isotope of an element to decay. Also used for decay processes in general.

heat- Energy transfer via random molecular motions, resulting in gain or loss of internal energy.

heat engine- A device that changes internal energy to mechanical work.

hertz- (HERTS) The SI unit of frequency. One hertz (Hz) is one vibration per second.

hologram- (HOL-uh-gram) A three-dimensional version of a photograph produced by interference pat-terns of laser beams.

Hooke's law- The distance of stretch or squeeze (extension or compression) of an elastic material is directly proportional to the applied force.

Huygens' principle- (HI-gunz) Every point on any wave front can be regarded as a new point source of secondary waves.

hypothesis- (hi-POTH-uh-sis) An educated guess; a reasonable explanation of an observation or experimental result that is not fully accepted as factual until tested over and over again by experiment.

Hz- The symbol for hertz.

I J

impulse- (IM-puls) Product of force and time interval during which the force acts. Impulse equals momentum change.

inelastic- Term applied to a material that does not return to its original shape after it has been stretched or compressed. (Also called plastic.)

inelastic collision- A collision in which the colliding objects become distorted and/or generate heat during the collision.

inertia- (ih-NER-shuh) The reluctance of any body to change its state of motion. Mass is the measure of inertia.

infrared- Electromagnetic waves of frequencies lower than the red of visible light.

infrasonic- (in~-fruh-SON~-ik) Term applied to sound pitch too low to be heard by the human ear, that is, below 20 hertz.

in parallel- Term applied to portions of an electric circuit that are connected at two points and provide alternative paths for the current between those two points.

in phase- (EAYZ) Term applied to two or more waves whose crests (and troughs) arrive at a place at the same time, so that their effects reinforce each other.

in series- Term applied to portions of an electric cir-cuit that are connected in a row so that the current that goes through one must go through all of tern.

instantaneous speed- (in-stan-TAY-nee-us) Speed at any instant of time.

insulator- (IN-suh-lay-ter) (a) A material that is a poor conductor of heat and that delays the transfer of heat. (b) A material that is a poor conductor of electricity.

interaction- A mutual action between objects where each object exerts an equal and opposite force on the other.

interference pattern- (in '-ter-FEER '-ens) A pattern formed by the overlapping of two or more waves that arrive in a region at the same time.

internal energy- The total energy stored in the atoms and molecules within a substance.

inverse-square law- A physical quantity varies inversely as another quantity squared. Example: Illumination varies inversely as the square of the distance from the source.

inversely- When two values change in opposite direc-tions, so that if one is doubled the other is reduced to one half, they are said to be inversely proportional to each other.

ion- (I-un) An atom (or group of atoms bound together) with a net electric charge, which is due to the loss or gain of electrons.

iridescence- (ih-rih-DES-ens) The phenomenon whereby interference of light waves of mixed frequencies reflected from the top and bottom of thin films produces a spectrum of colors.

iris- (I-ris) The colored part of the eye that surrounds the black opening through which light passes. The iris regulates the amount of light entering the eye.

isotope- (I-suh-top) A form of an element having a particular number of neutrons in the nuclei of its atoms. Different isotopes of a particular element have the same atomic number but different atomic mass numbers.

J - The symbol for joule.

joule- (JOOL) The SI unit of work and of all other forms of energy One joule (symbol 1) of work is done when a force of one newton is exerted on an object moved one meter in the direction of the force.