Vibration: An oscillation, or repeating back and forth motion, about an equilibrium position.
Wave: a uniformly advancing disturbance in which the parts moved undergo a double oscillation; any wavelike pattern.
crests: One of the places in a wave where the wave is highest or the disturbance is greatest.
troughs: One of the places in a wave where the wave is lowest, or disturbance is greatest, in the opposite direction from a crest.
amplitude: the distance from the midpoint to the maximum ( crest ) of a wave or equivalently, from the midpoint to the minimum.
wavelength: 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: is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency.
hertz: the SI unit of frequency. One hertz (HZ) is one vibration per sencond.
transverse waves: A wave with vibration at right angles to the direction the wave is traveling.
longitudinal waves: a wave in which the vibration is in the same direction as that in which the wave is traveling, rather at right angles to it.
Doppler Effect: the change in frequency of a wave due to the motion of the source or of the receiver.
blue shift: the displacement of the spectrum to shorter wavelengths in the light coming from distant celestial objects moving toward the observer.
red shift: the displacement of spectral lines toward longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects. This is interpreted as a Doppler shift that is proportional to the velocity of recession and thus to distance.
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.