| Glossary | ||||||||||||||
| frequency
— rate at which a cyclic behavior repeats. Measured in hertz (Hz), where 1 Hz = 1 cycle per second or 1/s. Frequency is the inverse of the period. frequency spectrum — graph showing amplitude on the vertical axis and frequency on the horizontal axis. The frequency spectrum tells you the relative amplitudes of the different frequencies in a signal. friction — resistive force caused by motion that always acts to oppose motion. fulcrum — pivot point or center of rotation for a lever. fusion — nuclear reaction in which two nuclei merge together to form a larger nucleus. galvanometer — instrument used to detect very small electric currents by detecting the magnetic force on a loop of wire. gamma decay — radioactive process during which a nucleus goes to a lower energy state by emitting a high-energy photon called a gamma ray. gamma rays — highest frequency form of electromagnetic radiation. gas — phase of matter that flows to fill completely its container and contains particles that experience little or no attractive force to each other. gear — toothed wheel that meshes together with another toothed wheel in order to transmit motion. gear ratio — ratio between the rates that the last gear and the first gear rotate in a machine. Geiger counter — scientific instrument used to detect and count the rate of ionizing radiation. gravitational potential energy — form of potential energy due to gravity. Close to the Earth’s surface, gravitational potential energy is equal to mgh. Measured in joules (J). ground state — lowest energy level for electrons in an atom. half-life — average time for one-half of the atoms in a substance to decay radioactively. | harmonic
— vibrating mode of oscillation with a frequency that is an integer multiple of the frequency of the fundamental vibrating mode. heat — thermal energy that flows from one object to another due to differences in their temperatures or because one object is undergoing a phase change. Measured in joules (J). heat transfer — study of how thermal energy moves, often through conduction, convection, and/or radiation. heat transfer coefficient — measure of the rate of heat flow between a surface and a fluid per square meter of contact area per degree of temperature difference. The heat transfer coefficient h is measured in power per unit area per degree of temperature difference. In SI units, the heat transfer coefficient is measured in watts per square meter per degree Celsius (W m−2 ºC−1). hertz (Hz) — unit of frequency. One hertz = 1 cycle per second, or 1/s or s-1. Hooke’s law — restoring force of a spring is proportional to the displacement (extension or compression) of the spring. Usually expressed as F = −kx, where k is the spring constant and x is the displacement. horsepower (hp) — unit of power equal to 746 watts. hypothesis — tentative explanation that may be tested and verified or revised based on the outcome of observations and experiments. ideal gas — theoretical gas of randomly moving point particles that interact only through elastic collisions with each other and the walls of their container. ideal gas law — relationship between pressure, volume, temperature, and the number of particles for an ideal gas. Usually expressed as PV = NkBT. ideal mechanical advantage — ratio of the distance moved by the input force to the distance moved by the output force. The ideal mechanical advantage corresponds to a machine with no efficiency losses. | |||||||||||||
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