Definitions of terms used in the reading selections on this site. For additional help with definitions, go to




ACID Any substance that, when dissolved in water, has a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals to form salts.


The study of how air behaves when it passes over objects


A lightweight aircraft made of a bag-like structure filled with a lighter-than-air gas—helium or hydrogen—and equipped with a propulsion and steering system.


A medieval chemical philosophy that combined primitive chemistry, superstition, and showmanship. Alchemy aimed to discover a way to turn common metal into gold and to find a medicine that would cure all ills, including old age.


A mixture of two or more elements, at least one of which is a metal. The resulting product has metallic properties.


The positive electrode in an electric circuit.


A massive block of iron, steel, or rock used as a surface for hammering or chiseling hot metals.


A piece of equipment used for a specific purpose.


The science of past human life and culture using fossils, artifacts, landscapes, architecture, and environmental analysis.


A naturally occurring fibrous mineral used for fireproofing, electrical insulation, building materials, brake linings, and chemical filters. When inhaled, asbestos fibers can cause cancer.


A rod connecting opposing wheels of a vehicle.

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BALL BEARING A ring-shaped track containing freely revolving, hard metal balls against which a rotating shaft or other part turns. Ball bearings reduce friction between moving parts of a machine.
BALLAST TANKS Watertight tanks on the bottom or sides of ships used to increase stability.
BARIUM CHROMATE (BaCrO4). An anti-corrosive agent used as a yellow pigment in paints.
BENZENE (C6H6) A colorless, flammable liquid derived from petroleum and used in a wide variety of chemical products, including DDT, detergents, insecticides, and motor fuels. Benzene can cause cancer.
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CADIUM SULFIDE (CdS). A yellow sulfide used chiefly as a pigment.
CALIBRATE To check, adjust, or determine by comparison with a standard.
CARBONATE A chemical compound that contains CaCO3.
CARCINOGEN Any substance or agent that promotes cancer.
CASSITERITE A hard, heavy, dark mineral; the chief source of tin.
CASTING Shaping metal by pouring it onto or into a mold.
CATHODE The negative electrode in an electric circuit.
CENTRIFUGE A machine that spins a sample at high speeds to separate molecules from solution, or particles and solids from liquids and immiscible (unmixable) liquids.
CHEMICAL PROPERTIES The characteristics of a substance that cause different behavior during chemical reactions.
CHEMICAL REACTION A process in which the composition or structure of a chemical is changed to form another substance.
CHARCOAL A black, porous material, composed mostly of carbon, that is used as a fuel, filter, and absorbent.
CHLOROPHYLL PIGMENT A green chemical substance in plants, required for photosynthesis.
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CHROMATOGRAPHY A process used to separate mixtures by virtue of differences in absorbency.
COAL A natural material formed from fossilized plants; made up of carbon with various organic and some inorganic compounds. Used as fuel.
COMPOSITE MIXTURE A mixture resulting from the combination of two or more substances that have different properties.
COMPOUND A chemical substance made by two or more elements in a fixed ratio.
CONDENSATION The process in which a gas or vapor changes to a liquid.
CONDUCTION Heat transfer between two masses by direct contact; heat always moves from warmer to cooler.
CONDUCTOR A substance that readily transmits electric current and heat.
CONVECTION A method of heat transfer during which heat is taken away from a source by the circular movement of liquid or gas.
CORE The dense, innermost layer of Earth, made up mostly of iron and nickel. Earth’s core is divided into a liquid outer core and a solid inner core.
CORROSION The gradual destruction of metal caused by a chemical reaction with its environment.
CRACKING TOWER Structures in petroleum refineries in which heavy hydrocarbon molecules are made, or “cracked,” into lighter ones during the manufacture of gasoline.
CRUCIBLE A vessel made of a heat-resistant substance such as graphite or porcelain, used for melting and heating materials.
CRUDE OIL Oil in its natural state from the ground. Crude oil is a mixture of hydrocarbons, oxygen, nitrogen, and sulfur.
CRUST The outermost solid layer of Earth.
CRYSTALLINE Being, relating to, or composed of a crystal or crystals.
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DECOMPOSITION The chemical breakdown of matter into simpler components.

¹The mass of a known volume of a substance, usually measured in grams per cubic centimeter (g/cm3).

²A measure of mass per unit of volume.

DESALINATION The removal of salt from water.
DETERIORATION A loss of quality over time.
DIESEL A fuel made from crude oil. It is commonly used in the type of engines that power trucks and buses.
DILUTE To make thinner or less concentrated by adding a liquid such as water.
DISPLACEMENT The weight or volume of a liquid or gas taken up by a floating body.
DISTILLATION The evaporation and subsequent collection of a liquid by condensation.
DOCKING The act of securing an arriving vessel to a pier with ropes.
DRY-CELL BATTERY A battery that has an electrolyte in the form of moist paste.
DUCTILE Capable of being stretched or drawn out into wires.
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EARTHQUAKE A shaking or vibration of the ground due to a shift and rapid release of energy in underground rocks.
ELECTRIC CIRCUIT The circular path along which electric current travels.
The flow of electrons through a conductor.
ELECTRODE A terminal in an electric circuit.
ELECTROLYSIS The process of breaking a compound apart using electricity.
ELECTROLYTIC CELL A cell that can conduct electricity.
ELEMENT A substance that cannot be divided using ordinary chemical reactions.
ETCH To cut into the surface of a material by the action of acid.
EVAPORATION The process whereby a liquid gains energy and becomes a gas.
EXPANSION The act or process of enlargement.
EXTRACTION The process of taking one substance out of another.
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FAULT A crack in Earth's crust caused by earthquakes.
FIBERGLASS Fine glass fibers often used as insulation. These fibers can also be bound together by plastic or resin to make a composite.
FILTRATE The liquid produced after filtering a suspension of a solid.
FORENSIC ANALYSIS Scientific analysis that is performed as part of legal or court proceedings.
FORGE FURNACE A furnace used to heat metal before it is shaped.
FOSSIL FUEL Any naturally occurring fuel containing carbon and hydrogen. Fossil fuels are formed by the decomposition of organic material.
FRACTIONATING The separation of a mixture of chemicals into its components.
FUNGICIDE A substance that destroys or inhibits the growth of fungi.
FUSION A reaction in which the nuclei of atoms combine to release large amounts of energy.
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GALAXY A large cluster of stars, gases, and dust held together by a shared gravitational pull.
GALENA A gray mineral; the principal ore of lead.
GANGWAY The removable walkway between a ship and a pier
GAS A state of matter in which particles can flow more freely than in solids or liquids. This property allows for rapid diffusion and even distribution throughout its container (examples: water vapor and oxygen).
GASOLINE A hydrocarbon mixture that is made from oil and is used as fuel in motor vehicles.
GENERATOR A machine that converts mechanical energy into electrical energy.
GEOLOGIST A scientist who studies the physical components and natural processes of Earth.
GRAIN The direction of the majority of the fibers in an object.
GRAPHITE A soft, steel-gray to black, stable form of carbon; used in lead pencils, lubricants, paints, and coatings.
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HEMATITE A black or blackish-red to brick-red mineral; the chief ore of iron.
HIDING PIGMENT The white pigment in a colored paint. It prevents deterioration of the substrate caused by ultraviolet light.
HYDROCHLORIC ACID A clear, highly acidic solution of hydrogen chloride.
HYDROFLUORIC ACID A weak, poisonous liquid acid; formed by solution of hydrogen fluoride in water
HYPOTHESIS A tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation.


INCENDIARY Causing or capable of causing fire.
INERT Not readily reactive with other elements.
INSULATION Any material that reduces the transfer of heat, sound, or electricity.
IODIDE A salt or ester of hydriodic acid.
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KEROSENE A fuel made from oil that is used in lamps, heaters, and jet engines.


LASER Acronym for Light Amplification by Stimulated Emission of Radiation. An optical device that produces an intense monochromatic beam of coherent light. Lasers have a wide variety of applications in industry and medicine.
LAW OF CONSERVATION OF MATTER The scientific principle which holds that mass in a closed system does not change and that matter is neither created nor destroyed in a chemical reaction.
LIMESTONE A sedimentary rock consisting mainly of calcium that was deposited by the remains of marine animals.
LIQUID Fluid matter whose volume does not change under constant temperature and pressure and whose shape mimics that of its container (example: water).
LUBRICANT Any substance, such as oil or grease, used to reduce friction between two solid surfaces.
LUSTER The appearance of a surface that relies on how well it reflects light.
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MAGNETITE An oxide of iron that is strongly attracted by magnets.
MALLEABLE Capable of being shaped using a hammer or a roller.
MANTLE A layer in Earth's structure that lies below the crust and above the core.
MASS The quantity of matter in an object or sample. The property of an object that causes it to have weight in a gravitational field.
MATTER Any object or material that has mass and takes up space.
MERCURY A metallic element, silver in color and liquid at room temperature; used in some thermometers. Mercury is poisonous if ingested into the body.
METEORITE A stony extraterrestrial mass that reaches the surface of Earth.
MICROORGANISMS Living organisms that are so small that they cannot be seen without the aid of a microscope.
MINERAL A natural compound that has a definite chemical composition. Compounds found in rocks, for example, are called minerals. Some minerals are inorganic salts that are required for the body's natural processes.
MINERAL SPIRITS A liquid made from petroleum that is commonly used as a thinner in paints and varnishes.
MIXTURE Two or more substances that can be physically separated.
MOUNTAIN A steep land mass at higher elevation than the ground around it; formed by shifting tectonic plates.
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NEWTON A unit of measurement describing the force required to accelerate a mass of one kilogram one meter per second per second.
NONTOXIC Not producing or resulting from poison.
NUCLEAR REACTION Any reaction that involves a change in the nucleus of an atom.


OPAQUE The property of an object that does not allow light to pass through.
ORE A mineral deposit which contains a metal that can be extracted.
OSMOSIS The flow of a liquid through a semi-permeable membrane to equalize the solute concentration on both sides of the membrane.
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PANNING A process in which water sifting is used to separate precious metals (gold, for example) from soil, sand, and rocks.
PERIODIC TABLE OF THE ELEMENTS A table showing all the known chemical elements arranged so that elements with similar properties are grouped together.
PERMAFROST Any land or solid area below ground level that remains frozen (below zero degrees Celsius) for longer than two years.
PETROLEUM Oil and its products.
PIGMENT An insoluble substance that gives color to another substance. Pigments are used to make dry paint and to color objects.
PLANET A large celestial body that orbits a star such as our Sun.
PLASTIC The quality of a material that allows it to be shaped or formed.
PLUTONIUM A radioactive metallic element used in the production of nuclear energy and explosives.
PRESERVATIVE A substance used to maintain freshness and prevent or retard decay, rotting, and/or spoilage.
PRIMER COAT (PAINT) The first coat of paint that helps the following coats to adhere to the surface being painted.
PRODUCT A substance that results from a chemical reaction.
PROSPECTOR One who explores landscapes for valuable mineral deposits.
PURE SUBSTANCE A substance that is not mixed with another.
PUTRIDITY An advanced state of decomposition characterized by a foul stench.
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QUANTITATIVE INFORMATION Information consisting of numerical data.


RADAR A device that uses radio waves to monitor distant objects.
RADIATION The release of waves or particles from a source. (Example: A light bulb radiates visible light).
RADIOACTIVITY The random release of matter or energy from the nucleus of an unstable atom.
RAW MATERIALS Materials in their natural, unprocessed, unmanufactured state.
REACTANT A substance that undergoes a chemical change during a chemical reaction.
REACTIVE METALS Metals capable of undergoing chemical reaction.
REACTIVITY The susceptibility of a substance to undergo a chemical reaction.
RESPIRATION A chemical process in which organisms make energy available for their life processes. One form of respiration (aerobic respiration) combines food and oxygen and gives off carbon dioxide and water.
REVERSE OSMOSIS A filtration process that pushes water through a membrane while keeping out dissolved salts and metallic ions. Reverse osmosis is used in desalination.
RICHTER SCALE A logarithmic scale used to measure the strength and magnitude of an earthquake. (The difference between an earthquake of magnitude 6 and one of magnitude 7, for example, is one-tenth that between earthquakes of magnitude 7 and 8.) Tremors with a magnitude of 1 on the Richter scale are very subtle; those with a magnitude of 10 are extremely violent and dangerous. The largest recorded earthquake, the Great Chilean Earthquake of May 22, 1960, measured 9.5 magnitude.
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SATURATED SOLUTION A solution of a substance that can dissolve no more of that substance.
SEDIMENTATION The settling of particles suspended in a fluid.
SEPARATION SCIENCE A term used to describe methods of separating mixtures (for example, chromatography and fractionation).
SILT Tiny rock particles that are smaller than sand particles but bigger than clay particles.
SLUICE A water channel, controlled at its lower end by a gate, used in the separation of minerals from water.
SMELTING The process of removing metals from ore compounds.
SODIUM CHLORIDE (NaCl) Common salt, a chemical compound used to flavor and preserve food. Sodium chloride is the salt most responsible for the salinity of the ocean.
SODIUM NITRATE (NaNO3) A type of salt that has long been used as an ingredient in explosives. It has antimicrobial properties when used as a food preservative.
SOLID A state in which matter is composed of tightly packed particles and has definite shape and volume (example: ice).
SOLUTE Any substance that is dissolved in another.
SOLUTION A liquid mixture of two or more dissolved substances with uniform dispersal of all molecules.
SOLVENT A substance that dissolves other substances (solutes).
SPRUE The passage through which molten material is channeled into a mold.
STAR A ball of hot gas, mostly hydrogen and helium, in outer space that gives off energy in the form of light and heat.
STERN The rear of a boat, ship, or other vessel.
SUPERNOVA The self-destructive explosion of a star, creating an extremely bright light that becomes invisible over weeks or months.
SWORDSMITH An artisan who makes and mends swords.
SYNTHETIC Manufactured, as opposed to naturally occurring.
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TARNISH Discoloration of the surface of a metal due to dirt or corrosion.
TECHNOLOGY The way people alter and shape matter—including tools, techniques, processes, and organizations—so that it can be applied to different and new situations.
TEMPERATURE A measure of how fast the particles of a substance are moving (fast movement has higher temperatures, slow movement has lower temperatures).
TEMPER To heat a substance and then control the cooling process in order to achieve a desired balance of hardness and flexibility.
TETRACHLOROETHYLENE (Cl2C=CCl2 ) A compound widely used for the dry cleaning of fabrics and for metal-degreasing.
THEORY In science, a hypothesis that has been rigorously and repeatedly tested according to the scientific method and is accepted as the framework that describes, and that can be used to predict, the behavior of a certain natural phenomenon.
THERMOMETER An instrument used to measure temperature. Units may be in Fahrenheit, Celsius, or Kelvins.
THERMOSCOPE An instrument used to measure changes in temperature.
THYROXIN An iodine-containing hormone, produced by the thyroid gland, that increases the rate of cell metabolism and regulates growth. Thyroxin is made synthetically for treatment of thyroid disorders.
TITANIUM DIOXIDE (TiO2) A white pigment used in making paints.
TOXICITY A measure of the degree to which a substance is poisonous.
TRENCH A long, narrow ditch. Also a long deep area on the ocean floor.
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UNIVERSE All matter and energy, including all of the galaxies and the space between galaxies, taken as a whole.


VOLCANO A natural opening in Earth's surface through which gases, ash, and molten rock erupt.




The force exerted on a mass by gravity.


A process that joins metals together by melting and reattaching them.


X-RAY A stream of high-energy photons, used for their penetrating power in radiography, radiology, radiotherapy, and scientific research.
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