#separator:tab #html:false #tags column:4 Motion A change in an object's position phys-terms Speed How fast an object moves: distance divided by time phys-terms Velocity Speed in a given direction phys-terms Acceleration How quickly velocity changes phys-terms Displacement The straight-line change in position, with direction phys-terms Distance The total length of the path traveled phys-terms Scalar A quantity with size only, like speed phys-terms Vector A quantity with size and direction, like velocity phys-terms Force A push or a pull phys-terms Net force The total of all forces acting on an object phys-terms Balanced forces Forces that cancel, causing no change in motion phys-terms Unbalanced forces Forces that do not cancel, causing a change in motion phys-terms Inertia An object's resistance to change in its motion phys-terms Mass The amount of matter in an object phys-terms Weight The force of gravity on an object phys-terms Gravity The force that pulls objects with mass toward each other phys-terms Friction A force that resists sliding between surfaces phys-terms Air resistance Friction from air pushing against a moving object phys-terms Terminal velocity The constant speed reached when air resistance equals weight phys-terms Momentum Mass times velocity phys-terms Impulse A force applied over time, changing momentum phys-terms Work Force applied over a distance phys-terms Power The rate of doing work phys-terms Energy The ability to do work or cause change phys-terms Kinetic energy Energy of motion phys-terms Potential energy Stored energy due to position or condition phys-terms Gravitational potential energy Energy stored in an object because of its height phys-terms Elastic potential energy Energy stored in stretched or squeezed objects phys-terms Thermal energy The total kinetic energy of the particles in an object phys-terms Heat Thermal energy moving from hot to cold phys-terms Temperature A measure of the average kinetic energy of particles phys-terms Conduction Heat moving through direct contact phys-terms Convection Heat moving by the flow of fluids phys-terms Radiation Energy traveling as waves, even through empty space phys-terms Wave A disturbance that carries energy phys-terms Frequency The number of waves passing a point per second phys-terms Wavelength The distance from one wave crest to the next phys-terms Amplitude The height of a wave from its rest position phys-terms Hertz The unit of frequency: one wave per second phys-terms Reflection Waves bouncing off a surface phys-terms Refraction Waves bending when they enter a new material phys-terms Diffraction Waves spreading as they pass an edge or opening phys-terms Absorption A material taking in wave energy phys-terms Transverse wave A wave in which particles move up and down across the wave's direction phys-terms Longitudinal wave A wave in which particles move back and forth along the wave's direction phys-terms Electromagnetic spectrum The full range of light waves from radio to gamma rays phys-terms Circuit A closed path for electric current phys-terms Current The flow of electric charge phys-terms Voltage The push that moves charge through a circuit phys-terms Resistance How much a material opposes electric current phys-terms Conductor A material that carries electricity or heat well phys-terms Insulator A material that carries electricity or heat poorly phys-terms Magnet An object that attracts iron and has two poles phys-terms Magnetic field The area around a magnet where it exerts force phys-terms Electromagnet A magnet made by passing current through a coil of wire phys-terms Static electricity A buildup of electric charge on an object phys-terms Atom The smallest unit of an element phys-terms Nuclear fission Splitting a large nucleus into smaller ones, releasing energy phys-terms Nuclear fusion Joining small nuclei into a larger one, releasing energy phys-terms Radioactive decay An unstable nucleus giving off particles or energy phys-terms Pressure Force per unit area phys-terms Buoyancy The upward push of a fluid on an object phys-terms Density Mass per unit of volume phys-terms Torque A twisting force phys-terms Centripetal force A force that pulls an object toward the center of a circle phys-terms Projectile An object thrown or launched and moving under gravity phys-terms Free fall Falling with only gravity acting phys-terms Efficiency The share of input energy that does useful work phys-terms