Chemistry Terms atomic number The atomic number of an element is the number of protons in the nucleus of each atom. chemical reaction A process in which atoms and molecules interact, resulting in the alteration of their molecular structures. covalent bond An atomic bond in which an electron is a resident of the outer electron shell of both atoms involved in the bond. electric charge The property that a particle must have in order to feel the electromagnetic force. It can be positive or negative. electromagnetic (EM) force The fundamental force of nature that a particle feels if it has electric charge. electron By far the lightest of the 3 particles that make up atoms. They orbit the nucleus and have an electric charge of -1.6 10-19 Coulombs. electron shell A spherical region centered on the nucleus of an atom in which an electron resides. From the inside out, the orbitals hold respectively 2, 8, 8, 18, 18, 32 electrons. element All atoms with the same number of protons in their nuclei are said to be atoms of the same element. endothermic (reaction) A chemical reaction that requires an input of energy to drive it. exothermic (reaction) A chemical reaction in which energy is released to the environment. ionic bond A bond between atoms in which an electron from one atom leaves and resides in the other shell of the other atom, giving both atoms a net electric charge such that they attract each other and stick together. metallic bond The kind of bond holding atoms together in metals. The bonding electrons are not residents of the outer shells of any atoms, but are free to move amongst the atoms. neutron One of the two types of particles that make up an atomic nucleus. Its electric charge is zero. non-metal Elements that do not exibit metallic properties. They occupy the upper right portion of the periodic table of elements. periodic table of elements A gridlike listing of the known elements that is arranged such that elements within vertical row have similar properties. proton One of the two types of particles that make up an atomic nucleus. It has an electric charge of +1.6 10-19 Coulombs. valence shell The outer electron shell of an atom.
Nuclear Physics Terms daughter isotope The isotope into which a radioisotope transforms. A radioisotope can have several possible daughter isotopes, depending on the process by which it decays. halflife The amount of time necessary for half a sample of a radioisotope to decay to its daughter isotope. This is different for each radioisotope. isotope Each nucleus has some number of protons and neutrons. A particular number combination is an isotope. radioactive decay The transformation of an unstable nucleus into another nucleus (or nuclei). radioisotope An isotope that is unstable (it will eventually decay to another isotope). strong nuclear force The force that holds together atomic nuclei. It's attractive between protons, between neutrons, and between a proton and neutron. Electricity Terms AC & DC Alternating Current and Direct Current. DC is electricity moving in one direction (batteries produce this). AC is current moving back and forth (this is how it comes out of electrical receptacles). Ampere see electric current Coulomb The standard international unit of electric charge. It's the amount of charge on about 6.2415 quintillion protons. electric circuit A closed loop around which electric current can flow. electric current The flow of electric charge. When charged particles move (usually when electrons flow through matter) they carry charge. Metric unit is the Ampere, which is one Coulomb per Second. electrostatic force The attractive or repulsive force between 2 charged particles. The particles experience this force regardless of their motion. energy A dynamic quantity in physics responsible for motion. kinetic energy The energy of motion. When an object with mass m is moving at speed v its kinetic energy is KE = ½mv². Joule The metric unit of energy. It's the amount of energy required to lift 1 kilogram (2.2 pounds) about 10 centimeters (about 4 inches). magnetic field The magnetic force field produced by moving charges that affects other moving charges. One can compute the total field due to many moving charges and thus simplify the computation of force on another moving charged particle.
magnetism The second componant of the electromagnetic force. Two particles only interact through this force only when they are both moving. The magnitude of the force depends on the speeds of the 2 particles and the direction of the force depends on the directions that both are moving. potential energy Energy that's stored in some form. Examples are chemical potential energy, gravitational, nuclear, & spring energy. power Rate of energy flow. Metric unit is the Watt, equal to one Joule per Second. voltage Electric potential, energy per charge. In a 120 volt wall socket, each Coulomb of electron charge carrys 120 Joules of energy. Metric unit is the Volt, which is one Joule per Coulomb. Watt see power Heat & Thermodynamics Terms conduction (of heat) Heat (the vibrational energy in a substance) can flow through a substance as vibrational energy is transferred between atoms. Materials that conduct heat poorly (like styrofoam) can be used as insulators. convection Fluid flow produced when a fluid in a gravitational field is heated from underneath, causing the fluid at the bottom to expand and become bouyant in the surrounding fluid, so that it rises. energy The ability to do work. It is a conserved quantity and appears in many forms. heat A form of energy. Heat in a material is the kinetic energy of the moving atoms that make it up. The higher the temperature, the faster the atoms are moving. joule The metric unit of energy. It's the kinetic energy of two kilograms moving at one meter per second. It's the energy required to lift one kilogram (2.2 pounds) about 10 centimeters. Kelvin scale The temperature scale used in science. The zero of the scale is "absolute zero," the temperature of an object with no heat in it. The freezing point of water at sea level is 273.15 K and the boiling point is 373.15 K. kinetic energy The energy of motion. When an object with mass m is moving with speed v, it has an amount of kinetic energy given by K = ½mv². light Light consists of particles called photons which have no mass but carry energy. All objects emit photons constantly, but our eyes can detect only photons of a narrow range of energies. potential energy Energy that is contained in some static way (gravitational, chemical, nuclear, spring, etc.)
pressure Force exerted by a fluid, measured in units of force per area (pounds per square inch or newtons per square meter). radiation The production of light (or other types of particles). All objects radiate constantly. temperature Heat spontaneously flows from regions of higher temperature to regions of lower temperature, so temperature is a measure of the heat content of a substance. Mechanics Terms acceleration The time rate of change of speed (how much faster the object is going every second). Standar international units are meter per second per second (m/s²). force The phenomenon causing acceleration, it is a push or pull. The American unit of force is the pound, and the standard international unit of force is the Newton. mass The mass of an object has two influences on its behavior. It's a measure of the object's inertia (the resistance to acceleration) and a measure of the affect of gravity on the object. Newton's 1st Law An object at rest will remain at rest and an object in motion will remain in motion at a constant speed and in a straight line unless acted upon by a net outside force. Newton's 2nd Law If a net force F acts on an object of mass m, then the object will accelerate and the magnitude of the acceleration will be given by F = ma Newton's 3rd Law While object A exerts a force on object B, B exerts an equal and opposite force on A. speed The rate of movement of an object. Standard international units are meters per second (m/s). In the US, we're more used to miles per hour (mph). velocity Like speed but specifying direction. Waves Terms energy A conserved quantity in nature. It's responsible for motion and can occur in kinetic or potential form. frequency For a traveling wave, the number of peaks that pass a point in one second. light Particles (photons) carrying energy but having no mass, they all move at high speed. The energy ranges of photons are called radio, infrared, visible, ultraviolet, X-ray, and gamma. The particles have a
wavelike behavior. They move as though they are riding on unseen waves, and the frequency of the wave is proportional to the amount of energy in the photon. photon See light. reflection A wave rebounding from an object or boundary (e.g. light reflects off a mirror). refraction A wave traveling from one medium to another can change its direction (e.g. light through a lens or prism). sound Pressure waves; they are created by moving object (e.g. vibrating pieces of musical instruments). wave A traveling oscillation through a medium. wavelength The distance between two successive oscillations of a wave.