Pitch and Overtone
Ever since the first man-ape, amidst bashing in the head of a rival for a mate, realized that a certain random series of sounds gave him pleasure, relieved his stress and sequencially destroyed the silent film era, there has been music. Like all men, this particular man-ape grew tired of the sound of a skull as it shattered to pieces and ventured out to find the next big thing.
Soon, nearly every man-ape in the jungle was either in a band or with a band. However, some of the smarter, less coordinated man-apes, in fear of being left out of the gene pool, invented physics. These brave few man-apes decided that they should apply their "physics" to music, which would surely impress the women. After many long Wednesday nights spent argueing over who got to be the Dungeon Master, cases upon cases of Tab, and one terribly unfortunate accident involving a plunger, the laws of the physics of music were born. And they were glorious.
The source of all sound, whether it be from a violin, drum, or screaming baby, is vibration. When an object vibrates, it pushes against the air (or whatever medium it is traveling through) around it, forming a zone of compressed air. This zone pushes on a zone around it, as does that zone, as does the next zone, etc. Rarefaction occurs as the medium springs past its begining pressure, causing a lower pressure in the zone. When zones of rarefaction and compression pump outward from the source of sound equal to the rate of the vibration, sound waves are formed. Sound waves, also called longitudinal waves, have spherical motion close to the source, and as strait lines far from the source as the curvature decreases.
Musical sounds are created by the oscillation of part or parts of instruments. Instuments are designed to create standing waves which cause, for example, a string to oscillate with a large, sustained amplitude. Suposedly, the strings of certain length will oscillate in such a manner that they produce pleasurable sound, or music. Standing waves, represented below, are the waves most musical instruments create while making sound. As humans, we are designed to hear several different characteristics of sound, like frequency, amplitude and wavelength. It's time to get down and dirty with the actual physics of music...onward to frequency.