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Grade 8 Science
The Physical Science Review
| Term | Definition |
|---|---|
| absolute brightness | The brightness a star would have if it were at a standard distance from Earth. |
| absolute zero | The temperature at which no more energy can be removed from matter. |
| acceleration | The rate at which velocity changes. |
| accuracy | How close a measurement is to the true or accepted value. |
| acid | A substance that tastes sour, reacts with metals and carbonates, and turns blue litmus red. |
| activation energy | The minimum amount of energy needed to get a chemical reaction started. |
| air resistance | The fluid friction experienced by objects falling through the air. |
| alcohol | A substituted hydrocarbon that contains one or more hydroxyl groups. |
| alkali metal | An element in Group 1 of the periodic table. |
| alkaline earth metal | An element in Group 2 of the periodic table. |
| alloy | A mixture of two or more elements, one of which is a metal. |
| alpha particle | A type of nuclear radiation consisting of two protons and two neutrons. |
| amino acid | One of 20 kinds of organic compounds that are the monomers of proteins. |
| amorphous solid | A solid made up of particles that are not arranged in a regular pattern. |
| apparent brightness | The brightness of a star as seen from Earth. |
| Archimedes principle | The rule that the buoyant force on an object is equal to the weight of the fluid, the object displaces. |
| asteroid belt | The region of the solar system between the orbits of Mars and Jupiter, where many asteroids are found. |
| asteroids | Rocky objects revolving around the sun that are too small and numerous to be considered planets. |
| astronomical unit | A unit of measurement equal to Earths average distance from the sun, about 150 million kilometers. |
| astronomy | The study of the moon, stars, and other objects in space. |
| atom | The basic particle from which all elements are made. |
| atomic mass | The average mass of all the isotopes of an element. |
| atomic number | The number of protons in the nucleus of an atom. |
| average speed | The overall rate of speed at which an object moves; calculated by dividing the total distance an object travels by the total time. |
| axis | An imaginary line that passes through Earths center and the North and South poles, about which Earth rotates. |
| balanced forces | Equal forces acting on an object in opposite directions. |
| barometer | An instrument used to measure atmospheric pressure. |
| base | A substance that tastes bitter, feels slippery, and turns red litmus paper blue. |
| Bernoullis principle | The rule that a stream of fast-movingfluid exerts less pressure than the surrounding fluid. |
| beta particle | A fast-moving electron that is given off as nuclear radiation. |
| big bang | The initial explosion that resulted in the formation and expansion of the universe. |
| binary star | A star system with two stars. |
| black hole | An object whose gravity is so strong that nothing, not even light, can escape. |
| boiling | The process that occurs when vaporization takes place inside a liquid as well as on the surface. |
| boiling point | The temperature at which a substance changes from a liquid to a gas; the same as the condensation point, or temperature at which a gas changes to a liquid. |
| buoyant force | The upward force exerted by a fluid on a submerged object. |
| calendar | A system of organizing time that defines the beginning, length, and divisions of a year. |
| carbohydrate | An energy-rich organic compound made of the elements carbon, hydrogen, and oxygen. |
| carboxyl group | A COOH group, found in organic acids. |
| catalyst | A material that increases the rate of a reaction by lowering the activation energy. |
| cellulose | A complex carbohydrate found in plant structures. |
| Celsius scale | The temperature scale on which water freezes at 0 degrees and boils at 100 degrees. |
| centripetal force | A force that causes an object to move in a circle. |
| chemical bond | The force that holds atoms together. |
| chemical change | A change in which one or more substances combine or break apart to form new substances. |
| chemical energy | A form of potential energy that is stored in chemical bonds between atoms. |
| chemical equation | A short, easy way to show a chemical reaction, using symbols. |
| chemical formula | A combination of symbols that represents the elements in a compound. |
| chemical property | A characteristic of a pure substance that describes its ability to change into a different substance. |
| chemical symbol | A one- or two-letter representation of an element. |
| chemistry | The study of the properties of matter and how matter changes. |
| cholesterol | A waxy lipid in animal cells. |
| chromosphere | The middle layer of the suns atmosphere. |
| closed system | A system in which no matter is allowed to enter or leave. |
| coefficient | A number in front of a chemical formula in an equation that indicates how many molecules or atoms of each reactant and product are involved in a reaction. |
| colloid | A mixture containing small, undissolved particles that do not settle out. |
| coma | The fuzzy outer layer of a comet. |
| combustion | A rapid reaction between oxygen and fuel that results in fire. |
| comet | A loose collection of ice, dust, and small rocky particles, typically with a long, narrow orbit. |
| communicating | The process of sharing ideas with others through writing and speaking. |
| complex carbohydrate | A long chain, or polymer, of simple carbohydrates. |
| composite | A combination of two or more substances that creates a new material with different properties. |
| compound | A pure substance made of two or more elements chemically combined. |
| compression | The part of a longitudinal wave where the particles of the medium are close together. |
| concentrated solution | A mixture that has a lot of solute dissolved in it. |
| concentration | The amount of one material in a certain volume of another material. |
| condensation | The change from the gaseous to the liquid state of matter. |
| conservation of matter | The principle stating that matter is not created or destroyed during a chemical reaction. |
| constellation | An imaginary pattern of stars in the sky. |
| controlled experiment | An experiment in which only one variable is manipulated at a time. |
| convection zone | The outermost layer of the suns interior. |
| convex lens | A piece of transparent glass curved so that the middle is thicker than the edges. |
| coordinate | A pair of numbers used to determine the position of a point on a graph. |
| core | The central region of the sun, where nuclear fusion takes place. |
| corona | The outer layer of the suns atmosphere. |
| corrosion | The gradual wearing away of a metal element due to a chemical reaction. |
| corrosive | The way in which acids react with some metals so as to eat away the metal. |
| cosmic background radiation | The electromagnetic radiation left over from the big bang. |
| covalent bond | A chemical bond formed when two atoms share electrons. |
| crater | A large round pit caused by the impact of a meteoroid. |
| crystal | An orderly, three-dimensional pattern of ions or atoms in a solid. |
| crystalline solid | A solid that is made up of crystals in which particles are arranged in a regular, repeating pattern. |
| dark energy | A mysterious force that appears to be causing the expansion of the universe to accelerate. |
| dark matter | Matter that does not give off electromagnetic radiation but is quite abundant in the universe. |
| data | Facts, figures, and other evidence gathered through observations. |
| data point | A point on a graph showing the location of a piece of data. |
| decomposition | A chemical reaction that breaks down compounds into simpler products. |
| density | The ratio of the mass of a substance to its volume. |
| diamond | A form of the element carbon in which the atoms are arranged in a crystal structure. |
| diatomic molecule | A molecule consisting of two atoms. |
| dilute solution | A mixture that has only a little solute dissolved in it. |
| directly proportional | A term used to describe the relationship between two variables whose graph is a straight line passing through the point (0, 0). |
| displacement | The length and direction of a straight line between starting and ending points. |
| distance | The length of a path between two points. |
| DNA | Deoxyribonucleic acid, one type of nucleic acid. |
| double bond | A chemical bond formed when atoms share two pairs of electrons. |
| ductile | A term used to describe a material that can be pulled out into a long wire. |
| eclipse | The partial or total blocking of one object in space by another. |
| eclipsing binary | A binary star system in which one star periodically blocks the light from the other. |
| elastic potential energy | The energy of stretched or compressed objects. |
| electrical conductivity | The ability of an object to transfer electric current. |
| electrical energy | The energy of moving electrical charges. |
| electrode | A metal strip that conducts electricity. |
| electromagnetic energy | A form of energy that travels through space as waves. |
| electromagnetic radiation | Energy that travels through space in the form of waves. |
| electron | A negatively charged particle that is found outside the nucleus of an atom. |
| electron dot diagram | A representation of the valence electrons in an atom, using dots. |
| element | A pure substance that cannot be broken down into other substances by chemical or physical means. |
| ellipse | An oval shape, which may be elongated or nearly circular; the shape of the planets orbits. |
| elliptical galaxy | A galaxy shaped like a round or flattened ball, generally containing only old stars. |
| endothermic change | A change in which energy is taken in. |
| endothermic reaction | A reaction that absorbs energy in the form of heat. |
| energy | The ability to do work or cause change. |
| energy level | A region of an atom in which electrons of the same energy are likely to be found. |
| enzyme | A biological catalyst that lowers the activation energy of reactions in cells. |
| equinox | The two days of the year on which neither hemisphere is tilted toward or away from the sun. |
| escape velocity | The velocity an object must reach to fly beyond a planets or moons gravitational pull. |
| ester | An organic compound made by chemically combining an alcohol and an organic acid. |
| estimate | An approximation of a number based on reasonable assumptions. |
| evaporation | The process that occurs when vaporization takes place only on the surface of a liquid. |
| exothermic change | A change in which energy is given off. |
| exothermic reaction | A reaction that releases energy in the form of heat. |
| extraterrestrial life | Life that exists other than that on Earth. |
| fatty acid | An organic compound that is a monomer of a fat or oil. |
| fluid | A material that can easily flow. |
| fluid friction | Friction that occurs as an object moves through a fluid. |
| force | A push or a pull exerted on an object. |
| free fall | The motion of a falling object when the only force acting on it is gravity. |
| freezing | The change from the liquid to the solid state of matter. |
| friction | The force that one surface exerts on another when the two surfaces rub against each other. |
| fuel | A material that releases energy when it burns. |
| fullerene | A form of carbon that consists of atoms arranged in the shape of a hollow sphere. |
| galaxy | A huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity. |
| gamma radiation | A type of nuclear radiation made of high-energy waves. |
| gas | A state of matter with no definite shape or volume. |
| gas giants | The name often given to the first four outer planets: Jupiter, Saturn, Uranus, and Neptune. |
| geocentric | A model of the universe in which Earth is at the center of the revolving planets and stars. |
| geostationary orbit | An orbit in which a satellite orbits Earth at the same rate as Earth rotates and thus stays over the same place all the time. |
| globular cluster | A large, round, densely-packed grouping of older stars. |
| glucose | A simple carbohydrate; the monomer of many complex carbohydrates. |
| graph | A picture of information from a data table; shows the relationship between variables. |
| graphite | A form of the element carbon in which a carbon atom is bonded tightly to three other carbon atoms in flat layers. |
| gravitational potential energy | Potential energy that depends on the height of an object. |
| gravity | The force that pulls objects toward each other. |
| greenhouse effect | The trapping of heat by a planets atmosphere. |
| group | Elements in the same vertical column of the periodic table; also called family. |
| halogen | An element found in Group 17 of the periodic table. |
| heliocentric | A model of the solar system in which Earth and the other planets revolve around the sun. |
| Hertzsprung-Russell diagram | A graph relating the surface temperatures and absolute brightnesses of stars. |
| heterogeneous mixture | A mixture in which pure substances are unevenly distributed throughout the mixture. |
| homogeneous mixture | A mixture in which substances are evenly distributed throughout the mixture. |
| horizontal axis (or x-axis) | A line that runs left to right along the bottom of a graph, on which the manipulated variable (or independent variable) is labeled. |
| Hubbles law | The observation that the farther away a galaxy is, the faster it is moving away. |
| hydraulic system | A system that multiplies force by transmitting pressure from a small surface area through a confined fluid to a larger surface area. |
| hydrocarbon | An organic compound that contains only carbon and hydrogen. |
| hydrogen ion | A positively charged ion (H+) formed of a hydrogen atom that has lost its electron. |
| hydroxide ion | A negatively charged ion made of oxygen and hydrogen (OH). |
| hydroxyl group | An OH group, found in alcohols. |
| hypothesis | A possible explanation for a set of observations or answer to a scientific question; must be testable. |
| indicator | A compound that changes color in the presence of an acid or a base. |
| inert gas | An element found in Group 18 of the periodic table. |
| inertia | The tendency of an object to resist any change in its motion. |
| inferring | The process of making an inference, an interpretation based on observations and prior knowledge. |
| inhibitor | A material that decreases the rate of a reaction. |
| instantaneous speed | The speed of an object at one instant of time. |
| inversely proportional | A term used to describe the relationship between two variables whose product is constant. |
| ion | An atom or group of atoms that has become electrically charged. |
| ionic bond | The attraction between oppositely charged ions. |
| ionic compound | A compound that consists of positive and negative ions. |
| irregular galaxy | A galaxy that does not have a regular shape. |
| isomers | Compounds that have the same chemical formula but different structures. |
| isotope | An atom with the same number of protons and a different number of neutrons from other atoms of the same element. |
| Kelvin scale | The temperature scale on which zero is the temperature at which no more energy can be removed from matter. |
| kinetic energy | Energy that an object has due to its motion. |
| Kuiper belt | A doughnut-shaped region that stretches from around Plutos orbit to about 100 times Earths distance from the sun. |
| law of conservation of energy | The rule that energy cannot be created or destroyed. |
| law of conservation of matter | The principle that the total amount of matter is neither created nor destroyed during any chemical or physical change. |
| law of conservation of momentum | The rule that in the absence of outside forces the total momentum of objects that interact does not change. |
| law of universal gravitation | The scientific law that states that every object in the universe attracts every other object. |
| lift | An upward force. |
| light-year | The distance that light travels in one year, about 9.5 million million kilometers. |
| line of best fit | A smooth line that reflects the general pattern in a graph. |
| linear graph | A line graph in which the data points yield a straight line. |
| lipid | An energy-rich organic compound made of carbon, oxygen, and hydrogen. Fats, oils, waxes, and cholesterol are lipids. |
| liquid | A state of matter that has no definite shape but has a definite volume. |
| lunar eclipse | The blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon. |
| main sequence | A diagonal area on an H-R diagram that includes more than 90 percent of all stars. |
| malleable | A term used to describe material that can be pounded into shapes. |
| manipulated variable | The one factor that a scientist changes during an experiment; also called independent variable. |
| maria | Dark, flat areas on the moons surface formed from huge ancient lava flows. |
| mass | A measure of how much matter is in an object. |
| mass number | The sum of protons and neutrons in the nucleus of an atom. |
| matter | Anything that has mass and occupies space. |
| mechanical energy | Kinetic or potential energy associated with the motion or position of an object. |
| melting | The change from the solid to the liquid state of matter. |
| melting point | The temperature at which a substance changes from a solid to a liquid; the same as the freezing point, or temperature at which a liquid changes to a solid. |
| meniscus | The curved upper surface of a liquid in a column of liquid. |
| metal | A class of elements characterized by physical properties that include shininess, malleability, ductility, and conductivity. |
| metallic bond | An attraction between a positive metal ion and the electrons surrounding it. |
| meteor | A streak of light in the sky produced by the burning of a meteoroid in Earths atmosphere. |
| meteorite | A meteoroid that passes through the atmosphere and hits Earths surface. |
| meteoroid | A chunk of rock or dust in space. |
| microgravity | The condition of experiencing weightlessness in orbit. |
| mixture | Two or more substances that are mixed together but not chemically combined. |
| model | Physical, mental, visual, and other representations of an idea to help people understand a concept that they cannot observe directly. |
| molecular compound | A compound that is composed of molecules. |
| molecule | A neutral particle made of two or more atoms joined by covalent bonds. |
| momentum | The product of an objects mass and velocity. |
| monomer | One molecule that makes up the links in a polymer chain. |
| moon | A natural satellite that revolves around a planet. |
| motion | The state in which one objects distance from another is changing. |
| nanotube | A form of carbon that consists of atoms in the form of a long, hollow cylinder. |
| neap tide | The tide with the least difference between consecutive low and high tides. |
| nebula | A large cloud of gas and dust in space, spread out in an immense volume. |
| net force | The overall force on an object when all the individual forces acting on it are added together. |
| neutral | A word used to describe a solution with a pH of 7. |
| neutralization | A reaction of an acid with a base, yielding a solution that is not as acidic or basic as the starting solutions were. |
| neutron | A small particle in the nucleus of the atom, with no electrical charge. |
| neutron star | The small, dense remains of a high-mass star after a supernova. |
| newton | A unit of measure that equals the force required to accelerate 1 kilogram of mass at 1 meter per second per second. |
| Newtons first law of motion | The scientific law that states that an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unless acted on by a force. |
| nonlinear graph | A line graph in which the data points do not fall along a straight line. |
| nonmetal | An element that lacks most of the properties of a metal. |
| nonpolar bond | A covalent bond in which electrons are shared equally. |
| nuclear fusion | The process by which hydrogen atoms join together in the suns core to form helium. |
| nucleic acid | A very large organic compound made up of carbon, oxygen, hydrogen, nitrogen, and phosphorus; examples are DNA and RNA. |
| nucleotide | An organic compound that is one of the monomers of nucleic acids. |
| nucleus | The central core of the atom; the solid inner core of a comet. |
| observatory | A building that contains one or more telescopes. |
| observing | The process of using one or more of your senses to gather information. |
| Oort cloud | A spherical region of comets that surrounds the solar system. |
| open cluster | A star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars. |
| open system | A system in which matter can enter from or escape to the surroundings. |
| optical telescope | A telescope that uses lenses or mirrors to collect and focus visible light. |
| orbit | The path of an object as it revolves around another object in space. |
| orbital velocity | The velocity a rocket must achieve to establish an orbit around a body in space. |
| organic acid | A substituted hydrocarbon with one or more of the COOH group of atoms. |
| organic compounds | Most compounds that contain carbon. |
| origin | The (0, 0) point on a line graph; where the x-axis and y-axis cross on a graph. |
| parallax | The apparent change in position of an object when seen from different places. |
| parameter | A factor that can be measured in an experiment. |
| particle accelerator | A machine that moves atomic nuclei at higher and higher speeds until they crash into one another, sometimes forming heavier elements. |
| pascal | A unit of pressure equal to 1 newton per square meter. |
| Pascals principle | The rule that when force is applied to a confined fluid, the increase in pressure is transmitted equally to all parts of the fluid. |
| penumbra | The part of a shadow surrounding the darkest part. |
| period | A horizontal row of elements in the periodic table. |
| periodic table | A chart of the elements showing the repeating pattern of their properties. |
| pH scale | A range of values used to express the concentration of hydrogen ions in a solution. |
| phase | One of the different apparent shapes of the moon as seen from Earth. |
| photosphere | The inner layer of the suns atmosphere that gives off its visible light; the suns surface. |
| physical change | A change in a substance that does not change its identity. |
| physical property | A characteristic of a pure substance that can be observed without changing it into another substance. |
| physics | The study of matter, energy, motion, and forces, and how they interact. |
| planetary nebula | A huge cloud of gas that is created when the outer layers of a red giant star drift out into space. |
| planetesimal | One of the small asteroid-like bodies that formed the building blocks of the planets. |
| plastic | A synthetic polymer that can be molded or shaped. |
| polar bond | A covalent bond in which electrons are shared unequally. |
| polyatomic ion | An ion that is made of more than one atom. |
| polymer | A large molecule in which many smaller molecules are bonded together. |
| potential energy | Stored energy that results from the position or shape of an object. |
| precipitate | A solid that forms from a solution during a chemical reaction. |
| precision | How close a group of measurements are to each other. |
| predicting | The process of forecasting what will happen in the future based on past experience or evidence. |
| pressure | The force exerted on a surface divided by the total area over which the force is exerted. |
| product | A substance formed as a result of a chemical reaction. |
| projectile | An object that is thrown. |
| prominence | A huge, reddish loop of gas that protrudes from the suns surface, linking parts of sunspot regions. |
| protein | An organic compound that is a polymer of amino acids. |
| proton | A positively charged particle that is part of an atoms nucleus. |
| protostar | A contracting cloud of gas and dust with enough mass to form a star. |
| pulsar | A rapidly spinning neutron star that produces radio waves. |
| quasar | An enormously bright, distant galaxy with a giant black hole at its center. |
| radiation zone | A region of very tightly packed gas in the suns interior where energy is transferred mainly in the form of light. |
| radio telescope | A device used to detect radio waves from objects in space. |
| radioactive decay | The process in which the atomic nuclei of unstable isotopes release fast-moving particles and energy. |
| radioactivity | The spontaneous emission of radiation by an unstable atomic nucleus. |
| reactant | A substance that enters into a chemical reaction. |
| reactivity | The ease and speed with which an element combines, or reacts, with other elements and compounds. |
| reference point | A place or object used for comparison to determine if an object is in motion. |
| reflecting telescope | A telescope that uses a curved mirror to collect and focus light. |
| refracting telescope | A telescope that uses convex lenses to gather and focus light. |
| remote sensing | The collection of information about Earth and other objects in space using satellites or probes. |
| replacement | A reaction in which one element replaces another in a compound or when two elements in different compounds trade places. |
| reproducibility | How close a group of measurements are to each other. |
| responding variable | The factor that changes as a result of changes to the manipulated, or independent, variable in an experiment; also called dependent variable. |
| revolution | The movement of an object around another object. |
| ring | A thin disk of small ice and rock particles surrounding a planet. |
| RNA | Ribonucleic acid, a type of nucleic acid. |
| rocket | A device that expels gas in one direction to move in the opposite direction. |
| rolling friction | Friction that occurs when an object rolls over a surface. |
| rotation | The spinning motion of a planet on its axis. |
| rover | A small robotic space probe that can move about the surface of a planet or moon. |
| salt | An ionic compound made from the neutralization of an acid with a base. |
| satellite | Any object that orbits around another object in space. |
| saturated hydrocarbon | A hydrocarbon in which all the bonds between carbon atoms are single bonds. |
| saturated solution | A mixture that contains as much dissolved solute as is possible at a given temperature. |
| science | A way of learning about the natural world through observations and logical reasoning; leads to a body of knowledge. |
| scientific inquiry | The ongoing process of discovery in science; the diverse ways in which scientists study the natural world and propose explanations based on evidence they gather. |
| scientific law | A statement that describes what scientists expect to happen every time under a particular set of conditions. |
| scientific notation | A mathematical method of writing numbers using powers of ten. |
| scientific theory | A well-tested explanation for a wide range of observations or experimental results. |
| semiconductor | A material that conducts current under certain conditions. |
| semimetal | An element that has some characteristics of both metals and nonmetals. |
| SI (Systme International dUnits) | International System of Units; a version of the metric system used by scientists all over the world. |
| significant figures | All the digits in a measurement that have been measured exactly, plus one digit whose value has been estimated. |
| sliding friction | Friction that occurs when one solid surface slides over another. |
| slope | The steepness of a line on a graph, equal to its vertical change divided by its horizontal change. |
| solar eclipse | The blocking of sunlight to Earth that occurs when the moon is directly between the sun and Earth. |
| solar flare | An eruption of gas from the suns surface that occurs when the loops in sunspot regions suddenly connect. |
| solar nebula | A large cloud of gas and dust, such as the one that formed our solar system. |
| solar wind | A stream of electrically charged particles that emanate from the suns corona. |
| solid | A state of matter that has a definite shape and a definite volume. |
| solstice | The two days of the year on which the sun reaches its greatest distance north or south of the equator. |
| solubility | A measure of how much solute can dissolve in a given solvent at a given temperature. |
| solute | The part of a solution present in a lesser amount and dissolved by the solvent. |
| solution | A well-mixed mixture containing a solvent and at least one solute that has the same properties throughout. |
| solvent | The part of a solution that is present in the largest amount and dissolves a solute. |
| space probe | A spacecraft that has various scientific instruments that can collect data, including visual images, but has no human crew. |
| space shuttle | A spacecraft that can carry a crew into space, return to Earth, and then be reused for the same purpose. |
| space spinoff | An item that has uses on Earth but was originally developed for use in space. |
| space station | A large artificial satellite on which people can live and work for long periods. |
| spectrograph | An instrument that separates light into colors and makes an image of the resulting spectrum. |
| spectrum | The range of wavelengths of electromagnetic waves. |
| speed | The distance an object travels per unit of time. |
| spiral galaxy | A galaxy with a bulge in the middle and arms that spiral outward in a pinwheel pattern. |
| spring tide | The tide with the greatest difference between consecutive low and high tides. |
| starch | A complex carbohydrate in which plants store energy. |
| static friction | Friction that acts on objects that are not moving. |
| structural formula | A description of a molecule that shows the kind, number, and arrangement of atoms. |
| sublimation | The change in state from a solid directly to a gas without passing through the liquid state. |
| subscript | A number in a chemical formula that tells the number of atoms in a molecule or the ratio of elements in a compound. |
| substance | A single kind of matter that is pure and has a specific set of properties. |
| substituted hydrocarbon | A hydrocarbon in which one or more hydrogen atoms have been replaced by atoms of other elements. |
| sunspot | A dark area of gas on the suns surface that is cooler than surrounding gases. |
| supernova | The brilliant explosion of a dying supergiant star. |
| supersaturated solution | A mixture that has more dissolved solute than is predicted by its solubility at a given temperature. |
| surface tension | The result of an inward pull among the molecules of a liquid that brings the molecules on the surface closer together; causes the surface to act as if it has a thin skin. |
| suspension | A mixture in which particles can be seen and easily separated by settling or filtration. |
| synthesis | A chemical reaction in which two or more simple substances combine to form a new, more complex substance. |
| telescope | A device built to observe distant objects by making them appear closer. |
| temperature | A measure of the average energy of motion of the particles of a substance. |
| tension | Stress that stretches rock so that it becomes thinner in the middle. |
| terrestrial planets | The name often given to the four inner planets: Mercury, Venus, Earth, and Mars. |
| thermal conductivity | The ability of an object to transfer electric current. |
| thermal energy | The total potential and kinetic energy of the particles in an object. |
| thrust | The reaction force that propels a rocket forward. |
| tide | The periodic rise and fall of the level of water in the ocean. |
| tracer | A radioactive isotope that can be followed through the steps of a chemical reaction or industrial process. |
| transition metal | One of the elements in Groups 3 through 12 of the periodic table. |
| triple bond | A chemical bond formed when atoms share three pairs of electrons. |
| umbra | The darkest part of a shadow. |
| unbalanced force | Forces that produce a nonzero net force, which changes an objects motion. |
| universe | All of space and everything in it. |
| unsaturated hydrocarbon | A hydrocarbon in which one or more of the bonds between carbon atoms is double or triple. |
| unsaturated solution | A mixture that contains less dissolved solute than is possible at a given temperature. |
| vacuum | A place that is empty of all matter. |
| valence electrons | The electrons that are in the highest energy level of an atom and that are involved in chemical reactions. |
| vaporization | The change of state from a liquid to a gas. |
| vector | A measurable quantity that consists of both a magnitude and a direction. |
| velocity | Speed in a given direction. |
| vertical axis (or y-axis) | A line that runs up and down along the side of a graph, on which the responding variable (or dependent variable) is labeled. |
| viscosity | A liquids resistance to flowing. |
| visible light | Electromagnetic radiation that can be seen with the unaided eye. |
| volume | The amount of space that matter occupies. |
| wavelength | The distance between the crest of one wave and the crest of the next wave. |
| weight | A measure of the force of gravity on an object. |
| white dwarf | The blue-white hot core of a star that is left behind after its outer layers have expanded and drifted out into space. |
| work | Force exerted on an object that causes it to move. |
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