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There are many notions in music which we use quite often and we take it quite casually. We use words like pitch, octave and harmonic quite frequently but we don't actually know what they mean. It turns out that each of these colloquial music terms have an interpretation in physics.
First off, pitch. A sound wave, like any other wave, is introduced into a medium by a vibrating object. The vibrating object is the source of the disturbance that moves through the medium. The vibrating object that creates the disturbance could be the vocal cords of a person, the vibrating string and sound board of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker. Regardless of what vibrating object is creating the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth motion at a given frequency. This frequency is directly related the pitch, so we sometimes same that pitch is frequency.
A special case of a pitch interval is an octave. Two notes which are separated by an octave have a frequency ratio of (the higher octave has double the frequency).
Next, the loudness is directly dependent on the intensity of the sound wave or, in the