vibration - an oscillation, or repeating back-and-forth motion, about an equilibrium position.
wave - a "wiggle in space and time"; a disturbance that repeats regularly in space and time and that is transmitted progressively from one place to the next with no actual transport of matter.
wave period - time it takes for two successive wave crests to pass a given point.
crest - one of the places in a wave where the wave is highest or the disturbance is lowest.
troughs - one of the places in a wave where the wave is lowest, or the disturbance is greatest, in the opposite direction of a crest.
amplitude - the distance from the midpoint to the maximum (crest) of a wave or, equivalently, from the midpoint to the minimum (trough).
wavelenght - the distance from the top of the crest of a wave to the top of the following crest, or equivalently , the distance between successive identical parts of the wave.
frequency - the number of events (cycles, vibrations, oscillations, or any repeated event) per time; measured in hertz ( or events per time). Inverse of a period.
hertz - the SI unit of frequency. One hertz (Hz) is one vibration per second.
transverse waves - waves with vibrations at right angles to the direction the waves are traveling.
longitudinal waves - waves in which the vibrations are in the same direction as that in which the waves are traveling, rather than at right angles to it.
Doppler Effect - the change in frequency of a wave due to the motion of the source of the receiver.
blue shift - an increase in the measured frequency of light from an approaching source; called the blue shift because the apparent increase is toward the high-frequency, or blue, end of the color spectrum. Also occurs when an observer approaches a source.
red shift - a decrease in the measured frequency of light (or other radiation) from a receding source; called the red shift because the decrease is toward the low-frequency, or red, end of the color spectrum.
shock wave - a cone-shaped wave produced by an object moving at supersonic speed through a fluid.
sonic boom - the sharp crack heard when the shock wave that sweeps behind a supersonic aircraft reaches the listener.