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Physical Science Glossary

absolute magnitude The brightness of a star if viewed from a distance of 32.6 light years; the scale ranges from -8 to 16, with -8 being the brightest and 16 the faintest (Lesson 31)
absolute zero The lowest point on the Kelvin scale (Lessons 19, 31)
acceleration The rate of change in velocity; includes speeding up, slowing down, and changing direction (Lessons 15, 16)
accuracy The closeness of a measurement to the actual value of what is being measured (Lesson 3)
accretion The process by which planets and other bodies in the solar system are created (Lesson 30)
acid A substance that donates protons (hydrogen ions); any compound that produces hydrogen ions in a solution (H+); a substance with a pH of less than 7 on the pH scale (Lesson 14, Lab 2)
acid rain Rain or any other type of precipitation that is abnormally acidic as a result of air pollution (Lesson 14)
actinide series Radioactive group of elements consisting of elements 89 through 103 on the periodic table (Lesson 9)
activated complex Highest point or peak on an energy diagram; represents the highest energy point between the reactant's and product's transition state (Lesson 12)
activation energy Amount of energy needed to start a reaction (Lessons 12, 13)
air resistance Friction acting on an object moving through the air (Lesson 16)
alkali A base; any substance having basic properties as opposed to acidic (Lesson 14)
alkali metal Metal element belonging to group 1 of the periodic table (Lesson 9)
alkaline earth metal Metal element belonging to group 2 of the periodic table, not including hydrogen (Lesson 9)
alpha particle A positively charged particle emitted during the radioactive decay of some unstable atoms (Lesson 25)
alternating current A flow of electric charge that regularly reverses direction (Lesson 23)
amplitude The maximum distance that the medium of a wave is displaced from its resting position (Lessons 20, 21)
anion A negatively charged ion (Lessons 8, 10, 11)
Antarctic Circle The circle of latitude south of which, on the solstices, every location experiences a period of continuous day or night (Lesson 29)
aphelion The point in a planet's orbit at which it is farthest from the Sun (Lesson 29)
aqueous Dissolved in water or relating to water (Lessons 12, 13)
Arctic Circle The circle of latitude north of which, on the solstices, every location experiences a period of continuous day or night (Lesson 29)
asteroid An irregularly shaped, rocky object that orbits the Sun and is believed to be formed from the same material as planets (Lesson 30)
asthenosphere Partly molten layer of the Earth that lies below the lithosphere (Lesson 26)
atmosphere The body of gases that surrounds a celestial body such as Earth (Lesson 28)
atmospheric pressure The weight of the air mass that surrounds Earth and exerts pressure on all points of the planet (Lesson 28)
atom Building block of matter, the smallest particle of an element (Lessons 5, 8, 10, 23, 24, 25)
atomic mass The sum of protons and neutrons in the nucleus of an atom; mass number (Lessons 8, 9)
atomic mass unit Special unit of mass used to express the mass of atoms and molecules (Lesson 8)
atomic number The number of protons in the nucleus of an atom (Lesson 9)
Atomic Theory Proposed explanation of the structure, properties, and behavior of the atom (Lesson 8)
atomic structure The structure of an atom, consisting of a nucleus with a positive charge that is surrounded by negatively-charged electrons (Lesson 24)
attraction An electric or magnetic force that acts between oppositely charged bodies; bring together (Lesson 24)
average speed The average of all speeds traveled during a given time; the total distance divided by the time it takes to travel that distance (Lesson 15)
average velocity Velocity of an entire trip, found by dividing the change in distance by the time it took to travel the distance (Lesson 15)
axis The invisible line on which the Earth rotates that runs through the Earth from the North Pole to the South Pole (Lesson 29)
background radiation Radiation that occurs naturally in the environment or is received as cosmic rays (Lesson 25)
balanced force When all the forces in a system cancel each other out and the net force is 0 N (Lesson 15)
bar graph A graph using comparative bars of different lengths to represent data (Lesson 4)
base A substance that accepts protons (hydrogen ions); any compound that produces hydroxide ions (OH-); a substance with a pH of more than 7 on the pH scale (Lesson 14, Lab 2)
base units Seven units of measurement that are considered to be "dimensionally independent," according to the BIPM (Lessons 3, 15)
beta particle An electron given off by an unstable nucleus (Lesson 25)
The Big Bang Theory The theory on the origins of the present day universe that states that the universe started as a small mass that gradually expanded to its current size and shape (Lesson 31)
binary compound A compound made up of only two elements (Lesson 11)
biochemical A type of sedimentary rock that is formed from the remains of organisms (Lesson 27)
black hole An extremely dense region of space where the gravitational pull is so massive that nothing can escape its force (Lesson 31)
boil To reach the boiling point and change from a liquid to vapor (Lesson 7)
boiling point Temperature at which a liquid boils; the temperature at which a substance changes from a liquid to a gas (Lesson 7)
bond Attractive force that holds atoms and ions together (Lesson 10)
Boyle's Law The pressure and volume of a gas at a constant temperature are inversely proportional to each other. (Lesson 6)
brittle Easily shattered or broken (Lessons 9, 26)
buffer A solution that is able to resist large changes in pH (Lesson 14)
buoyancy Upward force exerted on an object in liquid that causes it to float because the liquid has a greater density than the object (Lesson 13)
catalyst A substance used to speed up a chemical reaction but that is not consumed in the reaction (Lesson 12)
cation A positively charged ion (Lessons 8, 10, 11)
caustic Capable of destroying, damaging, or eating away at another substance; any chemical substance that burns or destroys living tissue (Lesson 14)
cementation The last stage in the formation of sedimentary rock; formed when mineral material bonds with sediment clasts (Lesson 27)
centrifugal force The outward push on an object when it is moving in a circle (Lesson 16)
centripetal acceleration The acceleration of an object traveling around a circle or portion of a circle as it constantly changes direction (Lesson 16)
centripetal force A force that continuously changes the direction of an object to make it move on a circular path (Lesson 16)
chain reaction A rapid series of nuclear reactions triggered by the release of neutrons during fission; can be controlled or uncontrolled (Lesson 25)
Charles's Law At a constant pressure and with a fixed amount of gas, volume and temperature are directly proportional to each other. (Lesson 6)
chemical bond Attractive force that holds atoms or ions together (Lesson 10)
chemical change Alteration of a chemical property of a substance that results in the formation of a new substance (Lessons 5, 13)
chemical equilibrium Type of reversible reaction occurring when the rate of the forward reaction is equal to the rate of the reverse reaction (Lesson 12)
chemical equation A representation of a chemical reaction using chemical symbols and formulas (Lesson 12)
chemical formula A way of writing a compound's name using symbols; a formula used to describe the number and type of atoms or ions in an element or compound (Lesson 11)
chemical property A characteristic of a substance that describes a type of chemical change it can undergo (Lesson 5)
chemical reaction A process by which one substance is transformed into another; a process in which a chemical change occurs (Lessons 9, 12)
chemistry Study of the properties, composition, structure, and reactions of matter (Lesson 5)
circle graph A graphic representation of the parts that make up a whole amount; also called a pie chart (Lesson 4)
circuit A complete path around which electric current can flow (Lesson 23)
circumference The perimeter, or distance around, a circle; the distance around the widest point of a sphere (Lesson 29)
classical planets The eight planets of the solar system (Lesson 30)
clast A particle that is formed by the weathering of existing rock material (Lesson 27)
cleavage The tendency of certain minerals, rocks, etc to break in certain directions (Lesson 27)
closed system A system that is isolated from any forces except those acting inside it (Lessons 15, 16, 17)
cochlea The fluid-filled canal in the ear that contains nerve cells that vibrate to send electrical impulses to the brain (Lesson 21)
coefficient A number that is placed in front of a symbol or a compound formula in a chemical equation that indicates how many atoms or molecules of that substance are involved in each reactant and product (Lesson 12)
collide Come together, bump into each other (Lesson 12)
collision theory Theory that states for a reaction to occur, the particles in the reactants must come together and collide with enough energy to break the bonds and form new bonds (Lesson 12)
colloid Heterogeneous mixture of tiny particles dispersed evenly throughout a solid, liquid, or gas (Lesson 13)
color A physical property test that identifies the coloring of a mineral (Lesson 27)
coma The sphere of vaporized gas and dust that surrounds the nucleus of a comet as it approaches the Sun (Lesson 30)
Combined Gas Law The pressure and volume of a gas are inversely proportional to each other, but directly proportional to the temperature of that gas. (Lesson 6)
combustion reaction A chemical reaction that occurs when oxygen combines with other substances, often producing heat and light (Lesson 12)
comet A celestial body that orbits the Sun and is formed from dust, ice, rock fragments, and frozen methane and ammonia (Lesson 30)
compaction The process by which sedimentary rock is formed by the compression of clasts (Lesson 27)
compound A substance made from two or more elements chemically bonded together and that can be chemically broken down into those substances (Lessons 5, 8, 9, 10, 11)
compound machine Machine made of two or more simple machines (Lesson 18)
compression An area in a longitudinal wave in which the particles in the medium are spaced close together (Lessons 20, 21)
concave lens A lens that curves inward in the middle and is thicker at the top and bottom (Lesson 22)
concave mirror A mirror in which the inside of a curved surface is reflective (Lesson 22)
concentrate To make a mixture stronger by adding more of the solute (Lesson 13)
concentration A measure of the strength of a solution; the number of molecules of a substance in a determined volume (Lessons 12, 13)
condensation Phase change that occurs when a vapor or gas turns into a liquid (Lessons 7, 28, Lab 4)
conduction The transfer of thermal energy without a transfer of matter (Lesson 19)
conductor A material through which heat, electricity, or sound can flow easily (Lessons 23, 24, Lab 3)
conjugate acid The compound formed when a proton is added to a base; differs from a base pair by the presence of one proton, or H+ (Lesson 14)
conjugate base The compound formed when an acid loses a proton (Lesson 14)
control A standard of comparison in a scientific experiment (Lesson 1)
constant speed An object traveling at a steady speed (Lesson 15)
constructive interference Two or more waves that combine to produce a wave with a larger amplitude (Lessons 20, 21, 22)
Continental Drift Theory Theory that proposes that about 225 million years ago, the seven continents of the Earth originally came from one single continent (Lesson 26)
convection Heat transfer that occurs by the circulation of a moving liquid or gas (Lesson 19)
convection current The circular pattern of fluid formed by the heating and cooling of magma in the asthenosphere (Lesson 26)
convergent plate boundary Two plates on the Earth's crust that collide and push into each other (Lesson 26)
convex lens A lens that curves outward and is thicker in the middle (Lesson 22)
convex mirror A mirror in which the outside of a curved surface is reflective (Lesson 22)
core Hot mixture of metal, mostly iron and nickel, that makes up the center of the Earth (Lessons 26, 29)
corrosive Capable of damaging and destroying materials on contact (Lesson 14)
cosmology The study of the structure and evolution of the universe (Lesson 31)
covalent bond A chemical bond that occurs between atoms sharing a pair of valence electrons (Lesson 10)
covalent compound Type of compound formed when non-metals bond by sharing electrons (Lessons 11, 13)
crest The highest point of a wave above the rest position (Lesson 20)
critical angle The angle of incidence that causes light to refract at a 90 degree angle (Lesson 22)
critical point The temperature at which the liquid phase of a substance no longer exists and at which a substance will be a gas regardless of the pressure (Lesson 7)
crust The outer layer of the Earth (Lesson 26)
crystal A solid made up of molecules arranged in a fixed structure; i.e. salt (Lesson 11)
crystalline structure Atoms and molecules that are arranged in a fixed shape, such as those in a mineral (Lesson 27)
crystallize A form of solid made up of molecules that are neatly arranged in regular and specific repeating patterns (Lesson 13)
customary units The system of weights and measures used in the United States; also known as English units (Lesson 3)
data A body of facts, statistics, or information (Lesson 1)
data table Facts, statistics, or information displayed in column format (Lesson 4)
decomposition reaction A chemical reaction that occurs when a compound breaks down into simpler substances (Lesson 12)
density The measure of how heavy something is for its size; the state or quality of being dense; mass per unit volume (Lessons 5, 21)
dependent variable A part of an experiment or set of data that is affected by an event or another variable (Lesson 1)
deposition Phase change that occurs when a gas transforms into a solid, skipping the liquid phase (Lesson 7)
derived units Units of SI measurement that are made when the base units are combined algebraically (Lesson 3)
destructive interference Two or more waves that combine to produce a wave with a smaller amplitude (Lessons 20, 21, 22)
detrital A type of sedimentary rock formed from the compaction and cementation of clasts (Lesson 27)
diameter The distance from one point of a circle's or sphere's circumference to another when passing through the center point (Lesson 29)
diatomic element Pure elements that, in nature, form molecules containing two atoms of the same element; i.e. hydrogen exists as H2 (Lesson 10)
diatomic molecule Molecules made of only two atoms of either the same or different elements; i.e. NaCl or O2 (Lesson 10)
diffraction The bending of a wave as it moves around an obstacle or passes through an opening (Lessons 20, 21)
diffuse reflection Type of reflection that occurs when parallel light waves strike an uneven surface and bounce off in many different directions (Lesson 22)
dilute To make the strength of a mixture weaker or less concentrated by adding more solvent (Lesson 13)
direct current A type of continuous charge that moves in one direction; also known as DC (Lesson 23)
displacement Moving or putting out of the usual or proper place (Lessons 20, 21)
dispersion Method of dissolving that occurs when a substance breaks apart into tiny particles and spreads throughout the solvent (Lesson 13)
dissociation Method of dissolving that occurs when an ionic compound separates into ions as it dissolves (Lesson 13, Lab 2)
dissolve The process by which solid particles mix with a liquid and appear to become part of the liquid; i.e. dissolving salt in water; to pass into or become part of a solution (Lessons 11, 13)
divergent plate boundary Plate movement in which two plates move away from each other (Lesson 26)
Doppler effect sound: The change in a sound's frequency caused by the motion of the sound's source, the listener's position, or both (Lesson 21)
light: The measurable shift in color used to determine a celestial object's movement with respect to the observer (Lesson 22)
dosimeter Device that measures the amount of radiation to which one is exposed over time (Lesson 25)
double bond Type of bond formed when atoms share two pairs of electrons (Lesson 10)
double replacement reaction A chemical reaction that occurs when elements from two compounds replace each other to form two new compounds by exchanging positive ions (Lesson 12)
downdraft Fast-moving cool air (Lesson 28)
ductile Easily made into a wire (Lessons 9, 10)
dwarf planet A celestial body that is similar to a planet, but its gravitational pull is too weak to clear all debris from its orbit path (Lesson 30)
dynamic equilibrium A reversible reaction that is balanced so the concentration of the reactants is equal to the concentration of the products and does not change over time (Lesson 12)
eardrum The membrane that separates the outer and middle ear that vibrates at the same frequency as the sound waves that strike it (Lesson 21)
Earthís gravity Force that the Earth exerts on all objects at or near its surface (Lesson 5)
earthquake A series of vibrations in the Earth's crust caused by built up strain (Lesson 26)
eclipse When two celestial bodies align with the Sun, one blocking the light of the Sun from the other (Lesson 29)
effective collision Reactants that come together and collide with enough energy to break their bonds and form new ones (Lesson 12)
efficiency The ratio of work put out by a machine to the work put into that machine; a measure of how well something gets a job done with little waste of time and energy (Lesson 18)
electric charge A property that causes the particles that make up atoms (such as protons and neutrons) to attract or repel each other (Lesson 23)
electric circuit A closed path along which electrons can flow (Lesson 23, Lab 3)
electric current The continuous flow or movement of an electric charge (Lessons 23, 24, Lab 3)
electric field A region of space that is characterized by the presence of an electric force (Lesson 22)
electric force The attraction or repulsion between electrically charged objects (Lesson 23)
electrolyte Compound within the body that dissolves in water and separates into ions (Lessons 11, 13, Lab 3)
electromagnet A very strong temporary magnet that can be turned on and off (Lesson 24)
electromagnetic induction The motion of a conductor through a magnetic field to produce electric current (Lesson 24)
electromagnetic radiation Electromagnetic waves that transfer energy by traveling through matter or empty space (Lesson 22)
electromagnetic spectrum The entire range of frequencies of electromagnetic radiation (Lessons 22, 25)
electromagnetic wave A wave that is made up of changing electric fields and changing magnetic fields; considered a transverse wave (Lessons 20, 21, 22, 24, 25)
electromagnetism The relationship between electric and magnetic fields and their interactions with each other (Lesson 24)
electron A negatively charged particle located outside the nucleus of an atom (Lessons 8, 10, 19, 23, 24)
electron dot diagram A diagram that uses dots to show an element's valence electrons; also called a Lewis diagram or Lewis dot diagram (Lesson 10)
electrostatic field Space surrounding a static electric charge (Lesson 8)
element Any of 118 known substances that make up matter and cannot be separated into simpler substances; also called chemical element (Lessons 5, 8, 9)
empirical formula The simplest formula for a compound; shows the simplest ratio in which atoms can combine and form a compound (Lesson 11)
endothermic A reaction that absorbs or takes in energy from its surroundings (Lesson 12)
energy The ability to move or change matter; the ability to do work (Lessons 12, 17, 18)
energy diagram A graph plotting the energy change of a system as a chemical reaction proceeds (Lesson 12)
energy level The possible energy that electrons in an atom must have; the path of a given electron's orbit around a nucleus (Lesson 8)
enzyme A protein that acts as a catalyst for specific reactions (Lesson 14)
equilibrium State of balance; occurs in a system when opposing forces balance and cancel each other out to equal zero (Lesson 12)
equinox The time when the Earth is tilted neither towards nor away from the Sun, resulting in a night and day of equal length (Lesson 29)
evaporation Process that changes a liquid to a gas at temperatures below the boiling point (Lesson 7)
exosphere The highest region of the Earth's atmosphere (Lesson 28)
exothermic A reaction that releases or gives off energy (Lesson 12)
extrusive A type of igneous rock formed on Earth's surface (Lesson 27)
eye The calm, low-pressure center of a hurricane (Lesson 28)
family A column or group of elements on the periodic table (Lesson 9)
fission A nuclear reaction that involves the splitting of an atomic nucleus into smaller parts (Lesson 25)
flame test Procedure in chemistry used to detect the presence of certain metal ions; a sample is placed under a flame and the color of the flame identifies the metal in the sample (Lesson 9)
flux lines Magnetic lines of force that circle a magnet (Lesson 24)
focal point The point at which the light rays parallel to a mirror or lens meet or appear to meet (Lesson 22)
foliated Rock texture characterized by the presence of layered mineral grains (Lesson 27)
force An action that causes an object to accelerate; equal to the product of an object's mass and acceleration (Lessons 15, 16, 17, 18)
fossil fuel Naturally occurring organic compounds that undergo combustion reactions to provide energy (Lesson 12)
frequency The number of cycles of periodic motion that pass by a point in a given amount of time (Lessons 20, 21)
friction A force that opposes motion between two objects that touch (Lessons 15, 16, 18, 19, 20, 23)
fulcrum In a lever, the point around which a bar pivots (Lesson 18)
fusion A nuclear reaction in which the nuclei of two atoms combine to make a larger nucleus (Lessons 25, 31)
galaxy A system of stars, gas, and dust that is located within the universe (Lesson 31)
gamma ray A ray of energy emitted by an unstable nucleus (Lesson 25)
gas State of matter that has no definite shape or volume (Lesson 6)
gas law Any of a group of laws that illustrate the relationship between temperature, pressure, and volume in gases (Lesson 6)
Gay-Lussac's Law At a constant volume and with a fixed amount of gas, pressure and temperature are directly proportional to each other (Lesson 6)
geocentric model The model of the solar system that places the Earth at the center, with satellites orbiting around it (Lesson 30)
geographic poles Either of two fixed points on the surface of a planet; in this case, Earth (Lesson 24)
grain size The size of a rock's mineral crystals (Lesson 27)
gravitational potential energy The potential energy that exists between the Earth and every object on it due to the force of gravity (Lessons 17, 18)
gravitational pull The force produced by a mass that causes other objects to be attracted to it (Lesson 30)
gravity Attraction between two objects due to their masses that increases with mass and decreases with distance (Lessons 16, 17, 26, 30)
greenhouse effect The process by which gasses trap heat in the atmosphere, warming surface temperatures of a planet (Lesson 28, 30)
group A column of 18 elements on the periodic table; also called a family (Lesson 9)
hail A type of precipitation that is formed from ice crystals that condense within a thunderstorm cloud (Lesson 28)
half-life The time required for one half of a sample of a radioisotope to decay (Lesson 25)
halogen Non-metallic gaseous element belonging to group 17 of the periodic table of elements (Lesson 9)
hardness A physical property test that identifies the strength of a mineral (Lesson 27)
heat The transfer of thermal energy from one object to another due to a difference in temperature (Lesson 19)
heating curve Plot of temperature versus time showing the various states of a substance (Lesson 7)
heliocentric model The model of the solar system that places the Sun at the center, with satellites orbiting around it (Lesson 30)
heliosphere The region of the universe that is influenced by the solar wind (Lesson 30)
heterogeneous mixture A mixture composed of substances that are unevenly mixed (Lesson 13)
high pressure system Weather condition that occurs in areas of high atmospheric pressure and usually results in stable conditions (Lesson 28)
homogeneous mixture A mixture composed of substances that are evenly mixed and have a uniform composition, uniform appearance, and definite properties (Lesson 13)
Hubble's Constant The rate at which the universe is currently expanding (Lesson 31)
Hubble's Law The redshift in light coming from distant galaxies is proportional to their distance. (Lesson 31)
hurricane Powerful cyclonic storm that develops over warm subtropical waters (Lesson 28)
hydrocarbon Compound composed of hydrogen and carbon (Lesson 12)
hydronium ion Compound that results from adding a hydrogen ion to a water molecule (Lesson 14)
hypothesis pl. hypotheses; A proposition set forth as an explanation of a certain phenomenon (Lessons 1, 22, 29)
ideal machine A theoretical machine in which the input work is equal to the output work and no energy is lost (Lesson 18)
ideal mechanical advantage An object's mechanical advantage if there were no friction involved in the system (Lesson 18)
igneous rock A rock that is formed from hardened magma (Lesson 27)
inclined plane

A flat surface that is slanted; one of the six simple machines (Lesson 18)

independent variable A variable that is not affected by other variables or events in an experiment (Lesson 1)
index of refraction The ratio of the speed of light in a vacuum to the speed of light in a medium (Lesson 22)
indicator A substance that changes color to signal the presence of an acid or base (Lesson 14, Lab 2)
induction Method of charging an object with static electricity or without contact between the materials (Lesson 23)
inertia The tendency of matter to resist change to its motion, whether it is moving or at rest (Lessons 15, 16, 30)
infiltration Absorption of water into the ground or soil (Lesson 7)
The Inflation Theory The addition to the Big Bang Theory that explains that the universe expanded rapidly over a short period of time and that it is still expanding (Lesson 31)
infrasound Sound with frequencies too low to be heard by the human ear but that may be felt as vibrations (Lesson 21)
inorganic Compound that is not formed from plant or animal remains (Lesson 27)
input force The force that is applied to a machine; represented by Fin (Lesson 18)
input work The work that is done on a machine; represented by Win (Lesson 18)
inner core The innermost part of a core such as the dense, solid center of the Earth's core (Lesson 26)
insoluble Unable to dissolve; does not dissolve (Lesson 13, Lab 1)
instantaneous velocity The speed and direction of an object at any particular moment (Lesson 15)
insulator A material through which energy cannot flow easily (Lessons 19, 23, Lab 3)
intensity Energy and force per unit of area, volume, time, etc; the rate at which a wave's energy flows through a given area (Lessons 21, 22)
International System of Units (SI) The system of universal units of measurement based on the meter-kilogram-second system (Lessons 3, 5, 6, 31)
intrusive A type of igneous rock that is forced between pre-existing rocks or layers (Lesson 27)
ion An atom that is electrically charged as a result of having more or less electrons than protons (Lessons 8, 10, 11, 13, 14, 23)
ionic bond Attractive force that holds ions together (Lesson 10)
ionic compound Chemical compound of cations and anions held together by ionic bonds (Lessons 10, 11, 13)
ionization Process by which a neutral atom or molecule loses or gains electrons (Lesson 13)
isotope Atoms of an element that have the same number of protons but different numbers of neutrons, and therefore a different atomic mass (Lessons 8, 9, 25)
Jovian planets The gas rich, outer planets of the solar system: Jupiter, Saturn, Uranus, and Neptune (Lesson 30)
kinetics The study of the actions of forces and reaction rates in chemical reactions (Lesson 12)
kinetic energy The energy that an object possesses because of its motion (Lessons 6, 7, 17, 18, 19)
kinetic friction The friction between two moving surfaces (Lesson 15)
kinetic theory of matter Matter is made up of small particles, atoms, or molecules that are always in random motion. (Lesson 6)
Kuiper Belt The ring of asteroids and other celestial bodies located past the orbit of Neptune (Lesson 30)
lanthanide series Metallic group of elements located below the periodic table consisting of elements 57 through 71 (Lesson 9)
latitude A line that runs east-west on a map and measures the distance north or south from Earth's equator (Lesson 29)
lava Fluid, molten rock that has risen to the Earth's surface through a volcano or volcanic vent (Lesson 26)
law A phenomenon in nature that has been proven to occur whenever certain conditions are met; also the statement of the phenomenon (Lessons 1, 6)
Law of Conservation of Mass In a chemical reaction, matter cannot be created or destroyed. It is conserved. (Lessons 7, 12)
Law of Conservation of Mass and Energy Neither energy nor matter can be created or destroyed. They can only be changed or transformed from one form to another. (Lessons 7, 17)
Law of Conservation of Momentum When two objects collide in a closed system, the total momentum of both the objects remains the same before and after the collision. Any momentum lost by one object is equal to the momentum gained by the other object. (Lesson 15)
Law of Universal Gravitation Any two masses attract each other with a force equal to a constant multiplied by the product of the two masses and divided by the square of the distance between them. (Lessons 16, 30)
lever A bar that is free to pivot around a specific point; one of the six simple machines (Lesson 18)
light year The distance that light can travel during one year; 9.5 x 1012 kilometers (Lesson 31)
line graph A diagram of lines made from connected data points that represent change in a value (Lesson 4)
line of symmetry An imaginary line that divides a figure into two equal parts that are mirror images of each other (Lesson 27)
liquid State of matter that has a definite volume but no definite shape (Lesson 6)
lithosphere Layer of Earth formed by the crust and the upper mantle (Lesson 26)
longitudinal wave A wave that causes the medium to vibrate in a motion that is parallel to the direction of the wave (Lessons 20, 21)
loudness A physical response to the intensity of sound (Lesson 21)
low pressure system Weather condition that occurs in areas of low atmospheric pressure and usually results in some degree of precipitation (Lesson 28)
luminosity Astronomy: the rate at which a star gives off energy (Lesson 31)
luminous An object that gives off its own light (Lesson 22)
lunar month The time it takes the Moon to complete one full cycle of Moon phases, from new Moon to new Moon (Lesson 29)
luster A physical property test that identifies how a mineral reflects light (Lesson 27)
magma Molten, liquid rock of the lower mantle (Lesson 26)
magnetic domain An area that has a high number of electrons with magnetic fields that align (Lesson 24)
magnetic field Space surrounding a magnet that experiences the force of attraction or repulsion of the magnet; a region of space that is characterized by the presence of a magnetic force (Lessons 8, 22, 24, 30)
magnetic force The force a magnet places on another magnet, magnetic material, or moving charges (Lesson 24)
magnetic poles The regions where a magnet's force is the strongest; the points at which the Earth's magnetic force is strongest (Lesson 24)
magnetic variation The difference in the location of the magnetic and geographic poles at a given point (Lesson 24)
magnetosphere The magnetic field around Earth; it is strongest at the north and south magnetic poles (Lesson 24)
main-sequence phase The longest stage of a star's life cycle during which the star produces hydrogen fusion (Lesson 31)
malleable Able to be bent, reshaped, and hammered without breaking (Lessons 9, 10)
manipulated variable A variable that is altered to cause change within another variable (Lesson 4)
mantle The thickest of the Earth's layers, lies between the crust and the core (Lesson 26)
mass A measure of the amount of matter in an object; also, a measure of an object's inertia (Lessons 5, 15, 16, 17)
mass number The sum of protons and neutrons in the nucleus of an atom; also called atomic mass (Lessons 8, 9, 25)
matter Anything that has mass and takes up space (Lessons 5, 8, 24)
mean The sum of all the data in a set divided by the total number of pieces of data; a value midway between the values of other quantities (Lesson 2)
mechanical advantage Ratio of output force to input force; the number of times a machine increases, or multiplies input force (Lesson 18)
mechanical energy Energy associated with everyday objects; the total amount of potential and kinetic energy in an object (Lessons 17, 23)
mechanical wave A disturbance in matter that carries energy from one place to another (Lessons 20, 21, 22)
medium pl. media; Matter through which a force acts or an effect is produced (Lessons 20, 21, 22, 23)
melting Phase change that occurs when a solid changes into a liquid (Lesson 7)
melting point Same as the freezing point; the temperature at which a solid becomes a liquid and at which a liquid becomes a solid (Lesson 7)
mesosphere One of the upper layers of the Earth's atmosphere (Lesson 28)
metal Reactive element that is a good conductor of electricity and heat, located to the left of the 'staircase' on the periodic table (Lesson 9)
metallic Term used to describe a substance that is made of metal or carries the properties of a metal (Lesson 10)
metallic bond Bond formed between a metal cation and the shared electron around it (Lesson 10)
metalloid An element located along the 'staircase' on the periodic table that exhibits properties of both metals and non-metals (Lesson 9)
metamorphic rock A rock that is formed by changes to igneous or sedimentary rocks through heat and pressure (Lesson 27)
metamorphism The process in which metamorphic rock is formed by changes in exposure to heat and pressure (Lesson 27)
meteoroid Debris that is produced when asteroids collide with one another (Lesson 30)
meteorologist A scientist who studies the atmosphere, including climate and weather patterns (Lesson 28)
meter The most basic unit of length in the metric system (Lesson 3)
metric system The decimal system of weights and measures (Lesson 3)
mineral A solid compound that is formed from one or more elements that occur naturally (Lesson 27)
mineralogy The scientific study of minerals (Lesson 27)
miscible Capable of being mixed (Lesson 13, Lab 1)
mixture Substance composed of two or more substances mixed together (Lessons 5, 13)
Mohs' scale of hardness A scale that is used to rate the scratch resistance of a mineral (Lesson 27)
molecular formula The actual formula for a compound; shows the actual number of atoms in the compound and gives the types of atoms and the exact number of each type (Lesson 11)
molecule Smallest part of a compound that contains all chemical properties of the compound; two or more atoms held together by chemical bonds (Lessons 5, 10, 17, 23)
momentum A property of mass that is moving; equal to the product of an object's mass and velocity (Lesson 15)
motion The act or process of changing position (Lesson 15)
natural magnet Substance found in nature that has magnetic properties (Lesson 24)
neap tide The lower than average tide that is created when the Moon and the Sun are at a right angle relative to the Earth (Lesson 29)
nebula pl. nebulae; Collection of gas and dust particles found in space (Lessons 26, 30, 31)
negative acceleration A measure of a decrease in an object's velocity in the opposite direction as its motion (Lesson 15)
net charge The overall charge of an object (Lesson 23)
net force The sum of all the forces acting on an object (Lessons 15, 16)
neutral Physics and chemistry: Having no electrical charge (Lesson 8)
Chemistry: Having neither acidic nor alkaline qualities (Lesson 14)
neutralization A double displacement reaction between an acid and a base that produces two neutral substances: salt and water (Lesson 14)
neutron A particle of an atom that holds no charge; located in the nucleus (Lessons 8, 23, 24)
newton The force needed to move one kilogram at a rate of one meter per second squared; the SI unit for force (Lesson 15)
Newton's First Law of Motion Objects that are in motion will stay in motion unless they are acted upon by an outside force; objects that are not moving will stay still unless they are acted upon by an outside force. (Lessons 15, 30)
Newton's Second Law of Motion The force acting on an object is equal to the product of the mass of the object and its acceleration. (Lessons 15, 16)
Newton's Third Law of Motion For every force, there is an equal force in the exact opposite direction. (Lesson 16)
noble gas An element from the group of non-reactive, non-metal elements located in group 18 on the periodic table (Lesson 9)
nomenclature A set or system of names or terms (Lesson 11)
non-foliated Rock texture characterized by the absence of layered mineral grains (Lesson 27)
non-metal An element that is a poor conductor of heat and electricity; located to the right of the 'staircase' on the periodic table (Lesson 9)
non-silicate Minerals that do not contain bonded silicone and oxygen tetrahedrons (Lesson 27)
nuclear radiation Charged particles and energy given off by the nuclei of radioisotopes as they decay (Lesson 25)
nuclear reactor A device in which a nuclear chain reaction can be initiated, sustained, or controlled in order to generate heat and power (Lesson 25)
nucleus pl. nuclei; Chemistry: The dense core of an atom where the protons and neutrons are located (Lessons 8, 10, 23, 24, 25)
Earth and Space Science: The hard, rocky center of a comet (Lesson 30)
oceanic ridge Chain of underwater volcanic mountains (Lesson 26)
octet rule Atoms are happiest when their outer shell is filled with the maximum number of valence electrons. (Lesson 10)
ohm The unit of measurement for resistance (Lesson 23)
Ohm's Law The voltage in a circuit equals the product of the current and the resistance. (Lesson 23)
Oort cloud A hypothetical region that exists past the Kuiper Belt and is believed to be the region where long range comets originate (Lesson 30)
opaque Not permitting light to pass through at all (Lesson 22)
optics The study of invisible and visible light and vision; the use of optical technology (Lesson 22)
orbit The path of a celestial body around another object (Lesson 29)
orbital Space around the nucleus where the electrons are most likely to be located (Lessons 8, 9)
order of operations The step-by-step process by which equations are solved (Lesson 2)
ore A type of rock that contains a profitable amount of a metal mineral (Lesson 27)
outer core The liquid outside portion of the Earth's core (Lesson 26)
outermost shell The farthest orbital from the nucleus of an atom that still contains electrons (Lesson 9)
output force The force that a machine applies to an object; represented by Fout (Lesson 18)
output work The work that is done by a machine; represented by Wout (Lesson 18)
ozone One of the three forms of oxygen that help shield the Earth from harmful ultraviolet rays in the atmosphere (Lessons 28, 30)
Pangaea Name of the proposed landmass that was all of Earth's continents before breaking apart and drifting (Lesson 26)
parallel circuit An electric circuit with two or more paths through which current can flow (Lesson 23)
parent rock Igneous or sedimentary rock in its original state before metamorphism takes place (Lesson 27)
particle A small component of matter such as an atom, electron, or proton (Lessons 8, 22)
penumbra The part of a shadow where the light is not completely blocked (Lesson 29)
perihelion The point in a planet's orbit that is closest to the Sun (Lesson 29)
period periodic table: Row of elements on the periodic table; there are seven periods on the periodic table (Lesson 9)
waves:
The time needed for one full cycle of periodic motion (Lesson 20)
periodic table of the elements Chart that lists all of the elements according to their properties (Lesson 9)
permanent magnet Magnetized material that will not lose its magnetic properties (Lesson 24)
pH A measure of how acidic or basic a solution is (Lesson 14, Lab 2)
pH electrode An electrical device that measures pH (Lesson 14)
pH meter An electrical device that measures pH (Lesson 14)
pH scale A scale that ranges in value from 0 to 14 that is used to measure the pH of a solution (Lesson 14, Lab 2)
phase A physical condition of a substance; also called state of matter (Lessons 6, 19)
phase change Process in which a substance changes from one state of matter to another (Lesson 7)
phase change diagram A plot of temperature versus energy showing the various states of a substance, the conditions under which each phase exists, and the phase change that occurs between each state (Lesson 7)
phase diagram A plot of temperature versus pressure showing the various phases of a substance and the conditions under which each phase exists (Lesson 7)
photon A packet of electromagnetic energy (Lesson 22)
physical change Alteration of a physical property of a substance (Lessons 5, 7, 13)
physical property A characteristic of a substance that describes a type of physical change it can undergo (Lesson 5)
pictograph A graph or chart with symbolic figures that represent a certain amount of data (Lesson 4)
pitch Frequency of sound as perceived by a listener (Lesson 21)
planetary disk Thin disk of dust, gas, and debris that surrounds a protostar (Lesson 26)
plasma State of matter in which the electrons have been removed from atoms (Lessons 6, 25, 29, 31)
plate tectonics The process by which the Earthís plates continuously move over top of the mantle (Lesson 26)
polar A pair of opposite charges or poles (Lesson 13, Lab 1)
polarization Behavior of light when the light waves vibrate in only one plane (Lesson 22)
polyatomic ion An ion that contains two or more atoms bonded together (Lesson 11)
porphyritic A type of rock texture that has both large and small mineral crystals (Lesson 27)
potential energy The energy between two objects due to their position relative to each other (Lessons 17, 19, 23)
power The rate at which work is performed; the rate of energy transfer over time (Lesson 18)
precipitate A solid that forms or separates itself from a solution as a result of or during a chemical reaction (Lessons 5, 13)
precipitation The collective term for any form of water that falls to the Earth, including rain, snow, and ice (Lessons 7, 28, Lab 4)
precision A measurement of how exact a value is (Lesson 3)
pressure A force applied over an area (Lessons 6, 12)
product Substance formed as a result of a chemical reaction (Lesson 12)
projection formula Formula that shows a three-dimensional structure in two-dimensional form (Lesson 11)
property A distinctive characteristic (Lesson 5)
proton A positively charged particle located in the nucleus of an atom (Lessons 8, 14, 23, 24)
protostar An early stage in the evolution of a star (Lessons 26, 31)
pulley A wheel with a groove for a rope or chain; one of the six simple machines (Lesson 18)
pure substance Matter that has a fixed composition (Lesson 5)
qualitative Having to do with the qualities, character, or behavior of something (Lesson 1)
quantitative Having to do with numbers, measurement, or the amount of something (Lesson 1)
quark A particle of matter that is theorized to be one of the basic units of matter (Lesson 8)
radiation The transfer of energy by waves that move through space (Lesson 19)
radioactive Property of certain elements or isotopes of an element whose atomic nucleus is unstable and can emit charged particles (Lessons 9, 25)
radioisotope An atom that has an unstable nucleus; also called a radioactive isotope (Lesson 25)
rarefaction The area in a longitudinal wave in which the particles in the medium are spread out (Lessons 20, 21)
rate A comparison of two values where one is divided by the other (Lessons 2, 15, 16, 18)
ratio A comparison of two numbers using division; often represented by a fraction (Lesson 11)
reactant Substance that undergoes change when a chemical reaction occurs (Lessons 12, 13)
reaction A process by which one substance is transformed into another; a process in which a chemical change occurs (Lesson 9)
reaction rate How quickly reactants turn into products; speed at which a reaction occurs (Lesson 12)
reactive Readily or easily able to undergo a chemical change (Lesson 9)
real image An image that is formed at the point where light rays meet (Lesson 22)
redshift A shift to longer wavelengths emitted by a celestial body that indicates the object is moving away from Earth (Lessons 22, 31)
reference point An indicator used to orient further data; a point that is chosen to represent zero when calculating a change in a value (Lessons 17, 19)
reflection The return of a wave after striking a surface through which it cannot pass (Lessons 20, 21, 22)
refraction The bending of a wave as it enters a new medium (Lessons 20, 21, 22, 29)
regular reflection Type of reflection that occurs when parallel light waves strike a surface and bounce off in the same direction (Lesson 22)
repulsion The force that acts between like bodies of electric or magnetic charges to separate them; pushes away (Lessons 23, 24)
resistance The property of a conductor that works against the passage of current (Lesson 23)
responding variable A variable that changes as a direct result of the manipulated variable (Lesson 4)
resonance The state in which one object vibrates at or near the frequency of another, causing the second object to vibrate (Lessons 20, 21)
rest position The position of a medium when no energy is traveling through it (Lesson 20)
reversible reaction Chemical reaction in which forward and backward (reverse) reactions can take place at the same time (Lesson 12)
revolution One complete voyage of a celestial body around its point of orbit (Lesson 29)
rift valley Valley created when the plate under a continent is stretched until it breaks and then sinks (Lesson 26)
rock A mass composed of one or more minerals as well as rock fragments and volcanic glass (Lesson 27)
rock cycle The circular process of creating and recycling rock material that has no beginning and no end (Lesson 27)
rotation The spin of a celestial body on its axis (Lesson 29)
salt A product of a neutralization reaction; any ionic compound composed of cations and anions that has an overall neutral charge (Lesson 14)
satellite An object in the solar system that orbits the Sun or a planet (Lessons 29, 30)
saturated solution A solution that contains as much dissolved solute as possible under normal condition and at a given temperature (Lesson 13)
scattering Behavior of light when light is redirected as it passes through a medium (Lesson 22)
Scientific Method A method of research and experimentation for gathering, organizing, and sharing scientific information (Lesson 1)
scientific notation A way to express very large or small numbers as a number multiplied by a power of 10 (Lesson 2)
screw An inclined plane wrapped around a cylinder; one of the six simple machines (Lesson 18)
sedimentary rock A rock that is formed from the buildup and compression of sediments over time (Lesson 27)
semiconductor A substance in which its ability to conduct heat and electricity falls between conductors and insulators and is only effective under certain conditions; a substance able to conduct heat and electricity better than non-metals but not as well as metals (Lesson 9)
series circuit A circuit in which all of the parts of the electrical circuit are set up in one closed loop (Lesson 23, Lab 3)
shell Specific path or space within an atom where the electrons are most likely to be located; also known as an energy level or orbital (Lesson 9)
sidereal month The time it takes the Moon to revolve around the Earth once and reach the same place in the sky relative to the stars behind it (Lesson 29)
significant figure Every digit that is known in a measurement (Lesson 3)
silicate A group of minerals in which all the minerals contain bonded silicone and oxygen tetrahedrons (Lesson 27)
simple machine A tool that only requires one force to be applied for it to do work (Lesson 18)
simplest form When the numerator and denominator have no common factor except for 1 (Lesson 2)
single bond Type of bond formed when atoms share only one pair of electrons (Lesson 10)
single replacement reaction Chemical reaction that occurs when one element replaces another element in a compound (Lesson 12)
solar wind The flow of gas and charged particles from the Sun into space that forms the heliosphere (Lesson 30)
solid State of matter that has a definite volume and shape (Lesson 6)
solidification The process by which magma hardens and forms igneous rock (Lesson 27)
solstice The time when the Earth is tilted the most either towards or away from the Sun; there are two solstices every year (Lesson 29)
solubility Ability of one substance to dissolve in another substance; physical property that measures the maximum amount of solute that can be dissolved in a specific amount of solvent (Lesson 13, Lab 1)
soluble Capable of being dissolved (Lessons 11, 13, Lab 1)
solute In a solution, the substance that gets dissolved (Lesson 13, Lab 1)
solution Two or more different substances combined to form a homogeneous mixture (Lessons 11, 13, Lab 1)
solvent In a solution, the substance in which another substance is dissolved (Lesson 13, Lab 1)
sonic boom An explosion-like sound (as perceived from the ground) that is the result of the shock wave created by an aircraft flying faster than the speed of sound (Lesson 21)
specific heat The amount of heat necessary to raise the temperature of one gram of a material by one degree Celsius (Lesson 19)
spectator ion An ion that is present during a chemical reaction but does not participate in the reaction (Lesson 14)
speed The rate of change in position over time (Lesson 15)
spontaneous A natural process that occurs on its own without any help; unplanned (Lesson 12)
spring tide The higher tidal levels created when the Moon and the Sun are on opposite sides of the Earth (Lesson 29)
stable Nonreactive; resistant to chemical change (Lessons 9, 10)
star A mass of self-luminous gas (Lesson 31)
state of matter A physical condition of a substance; phase (Lesson 6)
static electricity A stationary electric charge that builds up in an insulated material (Lesson 23)
static friction Friction that cannot be overcome by applying a force on an object (Lesson 15)
steam Gaseous state of water, produced when water is heated to its boiling point and changes from a liquid to a gas (Lesson 7)
stratosphere The second layer of the Earth's atmosphere (above the troposphere); contains the ozone layer (Lesson 28)
storm surge A significant rise in sea level at the coastline, caused by the winds of a cyclone (Lesson 28)
streak A physical property test that identifies the color of a mineral in powder form (Lesson 27)
strong acid An acid that completely dissociates in water (Lesson 14)
strong base A base that completely dissociates in water (Lesson 14)
strong nuclear force The force of attraction that binds protons and neutrons together in the nucleus (Lesson 25)
structural formula Formula that shows how atoms are arranged within a molecule or ion; shows the bonding of atoms and ions and which elements are bonded to each other (Lesson 11)
subatomic particle A unit of matter smaller than an atom (Lesson 8)
subduction zone Collision of Earth's plates that results in one plate overlapping another (Lesson 26)
subscript Smaller numbers or letters set partly below the normal text (Lessons 11, 25)
sublimation Phase change that occurs when a solid is converted directly into a gas, skipping the liquid phase (Lesson 7)
supercell A type of thunderstorm in which the winds rotate; can lead to the formation of a tornado (Lesson 28)
superconductor A conductor with almost zero resistance at very low temperatures (Lesson 23)
supergiant An exceptionally large star whose diameter is more than 100 times that of the Sun (Lesson 26)
supernatant Liquid portion of a solution or suspension that remains after a precipitate has settled to the bottom of the container (Lesson 13)
supernova pl. supernovae; The last stage in the cycle of a star (Lessons 22, 26, 30, 31)
supersaturated solution A solution containing more than the maximum amount of solute that can normally be dissolved in a solvent at a given temperature (Lesson 13)
superscript Smaller numbers or letters set partly above the normal text (Lessons 11, 25)
surface area The amount of exposed area an object has; the total area of the outside of a three-dimensional shape or a two-dimensional figure with a closed boundary (Lessons 13, 29)
surface wave A wave that travels along a surface between two media (Lessons 20, 21)
suspension A heterogeneous mixture that separates into its parts over time (Lesson 13)
symbol Shorthand or abbreviation used to represent something else (Lesson 9)
synodic month The time it takes the Moon to complete one full cycle of Moon phases, from new Moon to new Moon; also called a lunar month (Lesson 29)
synthesis reaction Chemical reaction that occurs when two or more substances combine to form a single compound; also called a combination reaction (Lesson 12)
tectonic earthquake The most common type of earthquake; occurs along plate boundaries (Lesson 26)
temperature A measure of how hot or cold something is when it is compared to a reference point (Lesson 19)
temporary magnet Magnetized material that can lose its magnetic properties (Lesson 24)
terminal velocity The point at which a falling object stops accelerating because the force of air resistance equals the force of gravity (Lesson 16)
terrestrial planets The four silicate rich, inner planets of the solar system: Mercury, Venus, Earth, and Mars (Lesson 30)
texture The description of the size and arrangement of a rock's geometric composition (Lesson 27)
theory A general proposition or group of propositions that explain a phenomenon (Lesson 1)
thermal conductor Material that conducts heat energy well (Lesson 19)
thermal contraction Contraction of a substance due to a loss of heat (Lesson 19)
thermal energy A measure of the kinetic energy of molecules and atoms in an object (Lessons 17, 19)
thermal expansion A characteristic of matter that causes particles of matter to move farther apart when the temperature increases, therefore the substance takes up more space as it gets hotter (Lessons 6, 19)
thermal insulator Material that does not conduct heat energy well (Lesson 19)
thermodynamics The study of conversion of thermal energy into other forms of energy (Lesson 19)
thermosphere The region of the upper atmosphere in which temperature increases; includes all of the atmosphere above the mesosphere (Lesson 28)
thunderstorm A violent storm of thunder or lightning, usually accompanied by rain and sometimes hail (Lesson 28)
tide The daily rise and fall of ocean waters, created by the Moon's gravity and other forces (Lesson 29)
tornado Concentrated storms that are characterized by a funnel-shaped cloud and extreme winds (Lesson 28)
total internal reflection The complete reflection of a light ray back into its original medium (Lesson 22)
totality The period of time in an eclipse when the Sun or Moon is completely covered by the body passing in front of it (Lesson 29)
transform plate boundary Plate movement in which two plates slide past each other in opposite directions and plate material is neither produced nor destroyed (Lesson 26)
transformer An electric device that increases or decreases voltage in AC circuits (Lesson 23)
transition metal An element belonging to groups 3 through 12 of the periodic table (Lessons 9, 11)
translucent Permitting some light to pass through but diffusing it so that objects on the other side appear distorted or blurry (Lesson 22)
transmission line High voltage electrical wiring that carries a signal (such as electricity) long distances (Lessons 23, 24, 25)
transparent Any material that lets all or almost all visible light pass through (Lessons 13, 22)
transpiration Evaporation of water through a plant from the roots, through the vascular system, and into the atmosphere (Lesson 7)
transverse wave A wave that causes the medium to vibrate in a motion that is perpendicular to the direction of the wave (Lessons 20, 21, 22)
trench A deep valley in the ocean floor created when Earth's plates collide (Lesson 26)
triple bond Type of bond formed when atoms share three pairs of electrons (Lesson 10)
triple point The temperature and pressure at which all three phases of matter (solid, liquid, and gas) are present (Lesson 7)
Tropic of Cancer The point farthest north on Earth where the Sun will ever be directly overhead (Lesson 29)
Tropic of Capricorn The point farthest south on Earth where the Sun will ever be directly overhead (Lesson 29)
troposphere The lowest layer of the Earth's atmosphere; about 10km from the Earth's surface (Lesson 28)
trough The lowest point of a transverse wave below the rest position (Lesson 20)
Tyndall effect The scattering of light passing through a colloid (Lesson 13)
ultrasound Sound with frequencies too high to be heard by the human ear (Lesson 21)
umbra The part of a shadow where the light is completely blocked (Lesson 29)
unbalanced force A net force that is greater than or less than but not equal to 0 N in a system; unbalanced forces create acceleration (Lesson 15)
universal solvent A liquid that can dissolve almost anything, i.e. water (Lesson 13, Lab 1)
universe All of the matter that physically exists (Lesson 31)
unsaturated solution A solution that can dissolve more solute at a given temperature (Lesson 13)
updraft Fast-moving warm air (Lesson 28)
vacuum A space that is entirely devoid of matter (Lessons 8, 15, 17, 19, 22, 28, 30)
valence electron Electron within the outermost shell, or valence shell, of an atom (Lessons 9, 10, 11)
valence shell Outermost shell of an atom (Lesson 9)
vapor Gaseous state of a substance that is a solid or liquid at ordinary temperatures (Lessons 7, 28)
vaporization Phase change that occurs when a liquid changes to a gas (Lesson 7)
variable Something that is capable of being varied or changed (Lessons 1, 4)
velocity Change in position over time in a defined direction (Lessons 15, 16, 17)
vesicular A type of rock texture that is characterized by the presence of holes that formed from air bubbles during the hardening of magma (Lesson 27)
virtual image A copy of an image that is formed at the place from where the light rays seem to come (Lesson 22)
visible spectrum The range of wavelengths that are visible to the human eye (Lesson 22)
volcanic earthquake Earthquakes that result from the pressure placed on the Earth's crust when magma pushes through the Earth's interior (Lesson 26)
volcano A vent in the Earth's crust through which lava, steam, and ashes are expelled (Lesson 26)
voltage The difference in electrical potential energy between two places in an electric field; also known as potential difference (Lesson 23)
volt The SI unit of measurement for voltage (Lesson 23)
volume Amount of space occupied by an object (Lesson 5, 29)
waning When the Moon is going from full to new, or appearing to shrink (Lesson 29)
water displacement Moving or putting water out of its original place (Lesson 5)
water cycle The path water takes through its different states (solid, liquid, and gas), which is a never-ending movement of water between the sea, the land, and the air (Lessons 7, 28, Lab 4)
wave A disturbance that transmits energy from point to point through matter or space (Lessons 8, 20, 21)
wavelength The distance from the peak of one wave to the peak of the next (Lesson 20)
waxing When the Moon is going from new to full, or appearing to grow (Lesson 29)
weak acid An acid that only partially dissociates in water (Lesson 14)
weak base A base that only partially dissociates in water (Lesson 14)
weather The condition of the atmosphere over a limited area and time period (Lesson 28)
weather front The boundary where a difference in air mass density causes the air regions to interact and move (Lesson 28)
weather map Tool for showing patterns in weather and air movement (Lesson 28)
weather symbol A picture on a weather map that represents a specific weather condition (Lesson 28)
weathering The processes that cause exposed rock to break down (Lesson 27)
wedge A movable, V-shaped inclined plane; one of the six simple machines (Lesson 18)
weight A measure of the force of gravity acting on an object; calculated by multiplying an objectís mass by gravity (Lessons 5, 16)
wheel and axle A wheel that turns about a fixed point, the axle; one of the six simple machines (Lesson 18)
white light Visible light, such as that given off by the Sun (Lesson 22)
work A force that causes an object to move in the direction of the force; a change in energy (Lessons 17, 18, 19, 25)
x-axis The horizontal line on a graph (Lessons 4, 7, 15)
y-axis The vertical line on a graph (Lessons 4, 15)