Mechanical motion forms through the sound waves made by vibrating massive objects. Guitar, harp or piano strings are clear examples of the principle, but horns, percussive instruments and woodwinds also create vibrations that make sound waves. Even ordinary objects create sound waves if they vibrate.
Sound waves are mechanical in nature, making them differ from electromagnetic waves, which are responsible for light. This mechanical nature means that sound only propagates through a medium, whereas light can travel through a vacuum. This is why a bell in an air-tight, vacuum jar cannot make a sound, yet is still easy to see.
Sound waves have a variety of characteristics that relate to the characteristics of the vibrating object. For example, the pitch or frequency of the sound waves is directly related to the vibrating frequency of the object. Similarly, objects whose vibrations have a high amplitude produce sound waves with a high volume.
The sound produced by most objects is composed of innumerable vibrations within the object, each of which produce slightly different pitches. These minor frequencies are called harmonics, and the sum of their vibrations creates the overall tone. Usually tones have a single powerful harmonic, often called the fundamental tone.