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| image
— picture of an object that is formed by optical devices through reflection and/or refraction. image distance — distance between an optical element (such as a mirror or lens) and the image formed by it. impulse — (1) change in momentum of an object; (2) product of force multiplied by the time over which the force acts. Units either kg m/s (kilogram meter per second) or N s (newton second). incident ray — light ray from an object that strikes a surface or boundary between two materials. inclined plane — flat and smooth surface that is tilted at an angle with respect to an acceleration or force. Also called a ramp. incompressible — fluid that does not change its volume (or density) despite changes in pressure. independent variable — variable in an experiment that is typically changed by the experimenter in order to cause a change in the dependent variable. The independent variable is typically plotted as the horizontal or x-axis (the abscissa) in a graph. index of refraction — ratio of the speed of light in a vacuum to its speed in a material. A measure of how much a light ray bends when it passes from a vacuum into the material. inelastic collision — type of collision where the objects stick together after impact, are deformed, and/or convert some kinetic energy to heat. Momentum is always conserved in collisions, but energy is not conserved in an inelastic collision. In a perfectly inelastic collision, the objects stick together after impact. inertia — property of matter that resists changes in speed or direction. The property of inertia derives from an object’s mass. inertial reference frame — reference frame that has a zero or constant velocity (both speed and direction). information — describes how matter and energy are arranged in time and space. infrared radiation — form of electromagnetic radiation at somewhat lower frequencies than visible light. Often emitted as a form of radiant heat. | input arm
— distance on a lever between the location the input force is applied and the fulcrum. input force — force applied to a machine. instantaneous velocity — velocity of an object measured at a particular time (not over a time interval). intensity — power per unit area (or the ratio of power to area) for forms of traveling energy such as light and sound. Measured in watts per square meter (W/m2). inverse square law — any law in which a physical quantity varies inversely as the square of the distance from a location. ionization — process by which an atom or molecule becomes charged by the removal or the addition of an electron. isothermal process — thermodynamic process in which a system undergoes a change in pressure and volume while temperature is held constant. During an isothermal process, pressure and volume are inversely proportional to each other. isotopes — atoms that have the same number of protons but different numbers of neutrons. Isotopes will have the same atomic number (because they have the same number of protons) but different atomic masses (because they have different numbers of neutrons). joule (J) — unit of work and energy in the SI. A force of one newton, acting for one meter, requires one joule of work. Kelvin scale — absolute scale for temperature that starts at absolute zero and measures the average energy of atoms or molecules. Measured in kelvins (K). kilowatt-hour (kWh) — measure of consumed energy typically used by power companies. Equivalent to the energy transferred by one kilowatt of power in one hour. kinetic energy — energy due to mass in motion. Measured in units of joules (J). | |||||||||||||
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