Most sound arises from vibrating mechanical objects in a medium

Evidence

Sound, from a physical point of view, is a wave physically propagating in a medium, usually air, and in most cases is caused by a vibrating mechanical object. Exceptions can also be found, such as the electrical discharge of lightning. Some sources of sound waves, interesting within the scope of this book, are the speech organs of a speaker, the vibrating plates and the air column of a guitar body, and the diaphragm of a loudspeaker. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 131

Categorization

• DEFINE: Defines sound physically as wave propagation from vibrating sources, with lightning as the notable exception.