Physics of Sound - Essay Example

Physics of Sound Physics and music could look so different but the fact is that the two are closely related. Music is sound, which is a branch of physics. Advances in physics have always emanated from someone’s mind: relativity theory was borne of Einstein, Heinsenberg and Schrodinger came up with the quantum theory, and Beethoven saw the development of magnificent symphonies. Hence, physics and music could be considered as products of human mind. This paper considers sound as a wave and seeks to explain how its characteristics relate to the general characteristics of waves. As a form of sound, music would be analyzed in relation to how it gets produced and the traits that differentiate it from noise. The perception of sound by the brain explains how humans hear sound after the cochlea traps external vibrations. Introduction Vibrations and waves play an important role in everyday lives. Sound waves would be heard wherever we go. While some like music could be pleasant, others could be irritating and even dangerous. A vibrating object produces disturbances in the air surrounding it. According to Kirkpatrick and Francis (314), when the surfaces of these objects move outward, the surrounding air molecules get pushed away resulting in a compression and when the surfaces move inward, a partial void, referred to as rarefaction, gets created near the object. Due to pressure difference, the air molecules would rush back but they get pushed out again. Hence, the air molecules would keep vibrating back and forth near the surface of the object. In his mathematical theory on sound, Isaac Newton viewed sound as pressure waves which get transferred to the surrounding particles (Myers 134). These compressions and rarefactions, corresponding to high and low pressure regions respectively, would travel from the object as sound wave. Because this vibration of air molecules move in the same direction with motion of the wave, then, sound would be considered as a longitudinal wave. Just like all other waves, sound wave travels as energy and not mass. The air molecules do not merely move from one position to another, instead, they basically vibrate back and forth (Kirkpatrick and Francis 314). Myers (134) further notes that other than air, sound could travel in other media such as liquids and solids. Sound needs a medium to travel and cannot travel in a vacuum due to lack of molecules for vibration. Wave characteristics of sound The nature of sound could, therefore, be defined through standard wave characteristics. Loudness would be a direct component of the amplitude with sound intensity being the rightful physical description to use in this context. This intensity would directly depend on the quantity of wave energy which meets the area which is perpendicular to the direction of the wave at a specified time period. The intensity of sound would thus be expressed in Jm2s. Since dividing a joule by second yields the unit of power, Watt, Myers (134) defines sound intensity as the quantity of power that is transmitted through and area, expressed in watts per square meter (Wm-2). According to the inverse square rule – the intensity of sound is inversely proportional to the square distance from the source (Parker 8), – as the sound spreads, the intensity decreases explaining the relation of intensity and distance from source. Pitch is another characteristic but one that relates to frequency. Musical instruments’ strings that vibrate rapidly result in high pitched sounds. Temperature, density and humidity affect yet another factor, speed of sound (Myers 136). The equation (331 + 0.6T) m/s gives the speed of sound with T being the temperature in 0C, approximated at 343, 1,480 and 6,000 m/s in air, water and steel respectively at room temperature. The speed of sound has been found to be higher in liquids and solids than in air. Myers (135) notes that the threshold of human hearing is about 10-12Wm-2 above which most humans would experience pain. Human ear detects sounds between 20 and 20,000 Hz in pitch though age decreases the ability to hear sounds of higher pitch with Myers (137) noting that a 50 year old would hear up to a range of 15,000 Hz. While ultrasonic refers to sounds above human normal hearing range, infrasonic refers to those below the range. There are many organisms with ultrasonic capability including cats and dogs that hear sounds above 20,000 Hz. Echolocation refers to the ability of animals like dolphins and bats to emit sounds of high frequency for adaptation in their environment (Gunther 150). Larger animals like elephants communicate using infrasonic sound. Music Scientifically, music could be said to be sound with aesthetic characteristics. Sound and music were among the major studies in which the ancient Greeks greatly based their scientific studies. Myers (134) gives an example of Pythogoreans who derived his ideas from music’s harmonic sound and applied it to the whole universe. The Pythogoreans findings indicated that when sounded together, vibrating strings would produce pleasant sounds when the lengths of the strings are matched in whole number ratios. Since the frequency of the string when plucked depends on string length, some frequencies when sounded together yield pleasant sounds referred to as music as others produce noise. The difference in music and noise come about the combination of sound waves based on the principles of superposition to give sound wave with particular qualities. Noise would have random patterns but music would be repetitive and follow distinct patterns. Parker (2) defines music by tones with specific frequencies: rhythm related to the length of tones; intensity, either high or low; and quality or timbre which defines the difference in source of sound and makes it interesting. When the string is struck or plucked, it vibrates as standing waves in a number of modes. It is the frequency of this wave that would determine the tone, normally described by the sounded note. Music scales would consist of notes arranged in decreasing or increasing order of pitch. While stringed instruments would be dependent on vibrating air columns in the surrounding box, which causes vibration of a column of air and amplification of the sound, brass instruments would have the musician’s vibrating lips cause a vibration of the air contained in the tube of the horn. Similarly, in woodwind instruments, the air that would be blown across the reed would cause it to vibrate and the vibrations transferred to air column. For instruments with open ends like trumpets, antinodes would exist at near the open ends. For an instrument with double open ends, there will be two antinodes with the fundamental frequency being double the distance between the two antinodes or two times the effective length of the air column. With a single open end, an antinode would exist at the open end while the closed end would have a node with the distance between them being a fourth of a wavelength. As such, overtones would occur where the tube length is an odd number and multiple of a fourth of the wavelength. Bethell and Coppock (79) note that the size and number of these overtones would cause notes from varied instruments to have different qualities or timbres. Beats, referring to the rhythm in music, refers to pulsating sound intensity due to sound waves with slightly varied frequencies being interfered. Myers (140) notes that two waves with different frequencies would combine to yield a periodically increasing or decreasing sound. Hearing in humans According to Kirkpatrick and Francis (316), human perception of sound is a product of the brain being triggered by external vibration that would be transmitted and then converted to information signals by hearing organs. The brain interactively seeks to synchronize with frequencies similar in spectrum to human voice together with the difference in frequency and tones then producing the effective sound heard by humans. Hence, the external frequencies do not get recognized directly by the brain but first converted to information energy. Humans particularly love music because of what Manzelli (4) terms as resonance with the innate emotional and mental information brain structure. The scholar describes the cochlea in human ear that transforms external vibration to information signals in coordination with the brain which is then passed through stereocilia filaments. These external vibrations pass through ossicles causing the hearing bones to strike the upper closing membrane. The vibrations of varied wave composition would the pass through a fluid of varied densities in the cochlea’s inner helix allowing for distinction of the different sound forms in timbre, loudness and pitch. Finally, hair-like sensors referred to as stereocilia serves as a trapping system that transforms the vibrations into information signals which would then be transmitted through the acoustic nerve in the brain. The bone structure and concentration of pressure vibration on the small window in the eardrum further amplifies sound increasing the capability of hearing faint sounds. Conclusion Sound is a form of longitudinal wave that results from vibration of molecules and moves in the same direction as the vibrating molecules. Humans perceive it as a result of sensory stimulation of the brain. The cochlea serves as the basic hearing organ which converts air mechanical vibration into information energy impulse which the brain translates to produce sound. Sound could be noise and capable of harming human hearing organs if outside the human hearing range. But music appeals because the concerned sound waves would have particular repetitive qualities following a specified pattern. Works Cited Bethell, G., and D. Coppock. Physics First. New York, NY: Oxford University Press, 2000. Print. Gunther, L. The Physics of Music and Color. New York, NY: Springer, 2012. Print. Kirkpatrick, Larry D., and Gregory E. Francis. Physics: A World View. 6th ed. Belmont, CA: Thomson Learning Inc., 2007. Print. Manzelli, P. “Quantum Physics of Sound and Music.” The General Science Journal 10 (2003): 1 - 4. Print. Myers, R. L. The Basics of Physics. Westport: Greenwood Publishing Inc., 2006. Print. Parker, B. R. Good Vibrations: The Physics of Music. Baltimore, Maryland: The Johns Hopkins University Press, 2009. Print. Read More