acceleration— The rate that velocity changes per unit time and the direction it changes in. Computed from the change in velocity divided by tire change in time. Common units are meters per second squared (m/s2 )

　　acceleration due to gravity— The acceleration of an object that is only acted on by the force of the Earth's gravity. This value is given the symbol g and near the surface of the Earth it has a value of approximately 9.8 m/s2. The direction of the acceleration due to gravity is vertically downward.

　　accuracy— The closeness of an experimental measurement to the accepted or theoretical value.

　　acid— A substance that is a proton donor. The pH of an acid is less than 7.

　　analysis— A stage in the scientific method where patterns of observations are made. antioxidant — any substance that inhibits oxidation, including vitamin E, vitamin C, or beta carotene, and is thought to protect the body from the damaging effects of oxidation

　　aqueous solution— A solution in which the solvent is water.

　　arteries— The vascular tissue which carries blood away from the heart. astronomy— The study of planets, stars, and space.

　　atom— The smallest structure that has tire properties of an element. Atoms contain positively charged protons and uncharged neutrons in the nucleus. Negatively charged electrons orbit around the nucleus.

　　ATP— (Adenosine Triphosphate.)—A chemical that is considered to be the "fuel" or energy source for an organism.

　　atria— The chambers of the heart that receive blood.

　　base— A substance that is a proton acceptor. The pH of a base is greater than 7.

　　bacteria— one-celled organisms that are involved in fermentation, putrefaction, and infectious

　　diseases

　　calibration—The examination of the performance of an instrument in an experiment whose outcomes are known, for the purpose of accounting for the inaccuracies inherent in the instrument in future experiments whose outcomes are not known.

　　capillaries— Vascular tissue that receives blood from the arterioles and releases the blood to the venules.

　　catalyst— An agent that changes the rate of a reaction, without itself being altered by the reaction.

　　celestial equator— The extension of the Earth's equator out onto the celestial sphere. celestial poles— Tire extension of the Earth's north and south pole onto the celestial sphere.

　　celestial sphere— The imaginary sphere onto which all the stars are viewed as being on for the purposes of locating them.

　　cell membrane— An organelle found in all cells that acts as the passageway through which materials can pass in and out. This organelle is highly selectively permeable, only allowing materials to pass through that it "chooses" chemically.

　　cell wall— An organelle found primarily in plant cells and fungi cells, and also some bacteria. The cell wall is a strong structure that provides protection, support, and allows materials to pass in and out without being selectively permeable.

　　centripetal force— The net force that acts to result in the centripetal acceleration. It is not an individual force, but the sum of the forces in the radial direction. It is directed toward the center of the circular motion.

　　chemical change—A process that Involves the formation or breaking of chemical bonds.

　　chromosome— An organelle that contains the entire DNA of the organism.

　　component— The part of a vector that lies in the horizontal or vertical direction.

　　compound— A substance composed of more than one element that has a definite composition and distinct physical and chemical properties.

　　concentration— A measure of the amount of solute that is present in a solution. A solution that contains very little solute is called dilute. A solution that contains a relatively large amount of solute is said to be concentrated.

　　conclusion— The last stage of the scientific method where explanations are made about why the patterns identified in the analysis section occurred.

　　concentric model—Tire model of the solar system that places the Earth at the center with the planets and the Sun orbiting around it.

　　constellation— An apparent grouping of stars in the sky that is used for identification purposes. These stars are not necessarily near each other in space since they are not necessarily the same distance from the Earth.

　　continental rift— The region on a continent where new crust is being created, and the plates on either side of the rift are moving apart.

　　convergent boundary— A boundary between two of the Earth's plates that are moving toward each other.

　　cosmology— The study of the formation of the universe.

　　crystal— A solid in which atoms or molecules have a regular repeated arrangement. current— The flow of charge past a point per unit time; it is measured in Amperes (A).

　　cuticle— The top layer on a leaf. It Is a non-living layer consisting primarily of wax that is produced by the epithelium, a cell layer directly underneath.

　　cytoplasm— A jelly-like substance located in the cell where all of the internal organelles can be found. The cytoplasm consists primarily of water and supports the cell and its organelles.

　　cytoskeleton— Organelles that are the internal "bones" of the cell. They exist in thick and thin tubules.

　　decibel— A unit of measure for the relative intensity of sounds.

　　decimation— The celestial coordinate similar to that of latitude on the Earth. Declination measures how many degrees, minutes, and seconds north or south of the celestial equator an object is.

　　delta— A fan shaped deposit of material at the mouth of a river.

　　density— The mass of a substance for a given unit volume. A common unit of density is grams per milliliter (g/ml).

　　displacement— The change in position of an object. Computed from the final position minus the initial position. Common units of measure are meters (m).

　　divergent boundary— A boundary between two of the Earth's plates that are moving away from each other.

　　DNA— Contains all genetic material for an organism. The smallest units of DNA are called nucleotides.

　　ecliptic— The apparent path of the Sun across the sky over the course of a year.

　　electric potential energy— The energy due to an object's position within an electric field.

　　electromagnetic wave— A light wave that has an electric field component and a magnetic field component. An electromagnetic wave does not require a medium to travel through.

　　electrostatic force— The force that exists between particles due to their charge. Particles of like charge repel, particles of unlike charge attract.

　　element— The smallest entity that has distinct chemical properties. It can not be decomposed by ordinary chemical reactions.

　　ellipse— A geometric shape that is formed when a plane Is Intersected with a cone. In this case the plane intersects the cone at an angle so that a shape similar to a circle but stretched in one direction is formed. The orbits of the planets around the Sun represent ellipses.

　　endoplasmic reticulum— An organelle that is used to transport proteins throughout the cell.

　　energy— The ability to do work or undergo change. Kinetic energy is the energy of motion, while potential energy is stored energy.

　　enzyme — any one of the complex proteins that are produced by cells and act as catalysts in

　　specific biochemical reactions

　　epicycle—Smaller circles on which the planets traveled around the Earth in the geocentric model of the solar system. Epicycles were used to explain the retrograde motion of planets and help make the predicted positions of the planets match the observed positions.

　　equilibrium—A state at which the forward and reverse reaction proceed at the same rate.

　　focal length— The distance from a focal point to a mirror or lens.

　　force— That which acts on an object to change its motion; a push or pull exerted on one object by another. Common units are Newtons (N).

　　freefall— An object in one-dimensional motion that is only acted on by the force of the Earth's gravity. In this case its acceleration will be -g or g downward.

　　frequency— The number of cycles or repetitions per second. Frequency is also often measured as the number of revolutions per second. The common units of frequency are Hertz (Hz) where one Hertz equals 1/second.

　　frictional force— The force that acts parallel to surfaces in contact opposite the direction of motion or tendency of motion.

　　functional group— A group of atoms that give a molecule a certain characteristic or property.

　　gel electrophoresis—A process used in laboratories to determine the genetic makeup of DNA strands. This process involves the movement of chromosomes through a gel from one pole to the other. Magnetism is used to pull the chromosomes through the gel.

　　geology— The study of rocks and minerals. glacier— A large mass of snow-covered ice.

　　golgi apparatus—An organelle that packages proteins so that they can be sent out of the cell.

　　gravitational force— The attractive force that exists between all particles with mass. heliocentric model— The model of the solar system that places the Sun at the center with the planets orbiting around it.

　　heterogeneous— A mixture that is not uniform in composition. homogeneous— A mixture in which the components are uniformly distributed.