The Physics Behind Music SPH3U: Grade 11 Physics, University Preperation Igor Padure June 6, 2022
Sound is a form of energy obtained by rapidly vibrating objects that can be identified by sensory organs such as the ear (DiGiuseppe et al., 2011, p. 382). Vibrating objects produce longitudinal sound waves in fluids, and can produce either transverse or longitudinal waves in solids. Typically when these waves have properties that make them detectable to the human ear, they are referred to as sound. These are audible sound waves, and have a frequency between 20Hz to 20kHz. Infrasonic sound waves have frequencies below audible sound waves, and ultrasonic sound waves have frequencies above audible sound waves. Three basic properties of sound waves are speed, frequency and wavelength. The speed of sound depends on the medium the wave passes through. In air, the speed of sound depends on the temperature, with the formula being: v= 331 m/s + (0.6 m/s/C) * T. In a 0? environment, the speed of sound is 343m/s. The frequency of a sound wave refers to the amount of oscillations in a given time period. A higher frequency means more oscillations per second, which increases the pitch of the sound. The wavelength of a sound wave refers to the distance between two successive in phase points on a wave. A longer wavelength decreases the frequency of the wave. The relationship between speed, frequency and wavelength can be seen in the universal formula for waves: v = Af. This formula applies to all types of waves, where v stands for speed, A stands for wavelength and f stands for frequency. Music is sound that is produced by a combination of musical notes obtained by a source that vibrates uniformly with one or more frequencies (DiGiuseppe et al., 2011, p. 454). In this case, both tuning forks and instruments create music. However, there is a difference between the music tuning forks make as compared to musical instruments. Tuning forks make musical notes that consist of one frequency, while musical instruments produce music that consists of the fundamental frequency along with other harmonics (DiGiuseppe et al., 2011, p. 454). Figure 1 shows the sound waves produced by a tuning fork compared to sound waves produced by other instruments. The distinct quality of sound that allows us to distinguish one instrument from another is referred to as timbre.
TIMBRE Tuning fork N Flute Voice Guitar 4 Figure 1. Sound waves of a tuning fork, flute, voice and guitar (SimplifyingThoery, n.d.) Other characteristics of musical sound include loudness, pitch and duration. The loudness of a sound is subjective, and depends on the ear hearing the sound. Generally loudness increases with greater amplitudes. Pitch is the highness or lowness of sound, and also depends on the observer's perception. Typically pitch increases with increased frequency. Duration is the specific length of time for a musical sound, for example how long or short a note or beat should be. Duration is composed of many aspects, such as the