Sound is a type of energy that travels in waves which are caused by vibrations. Characteristics of Sound. Vibrations: movements made rapidly back and forth. Sound Waves: an invisible transfer of sound energy as it travels away from the energy source. Wavelength: the distance between a point on one sound wave and a similar point on another sound wave. Frequency: The number of vibrations in a period of time is called the frequency of a vibration. Volume: The loudness or quietness of a sound is its volume. Read More...