Harmonic         Echo and Reverberation      Tuning Forks     Guitar Strings 

                Longitudinal Waves     Transverse Waves                Back to Physics


 Longitudinal Waves

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 In a longitudinal wave, particles of the medium are displaced in a direction parallel to energy transport As one individual particle is disturbed, it transmits the disturbance to the next interconnected particle. This disturbance continues to be passed on to the next particle. The result is that energy is transported from one end of the medium to the other end of the medium without the actual transport of matter




Tuning Forks


vibrating tuning fork


A tuning fork serves as a useful illustration of how a vibrating object can produce sound. The fork consists of a handle and two tines. When the tuning fork is hit with a rubber hammer, the tines begin to vibrate. The back and forth vibration of the tines produce disturbances of surrounding air molecules. As a tine stretches outward from its usual position, it compresses surrounding air molecules into a small region of space; this creates a high pressure region next to the tine


 Guitar Strings


sound wave

 As a guitar string vibrates, it sets surrounding air molecules into vibrational motion. The frequency at which these air molecules vibrate is equal to the frequency of vibration of the guitar string. The back and forth vibrations of the surrounding air molecules creates a pressure wave which travels outward from its source. This pressure wave consists of compressions and rarefactions. The compressions are regions of high pressure, where the air molecules are compressed into a small region of space. The rarefactions are regions of low pressure, where the air molecules are spread apart




             1st   Harmonic                                                                         



2nd  Harmonic

second harmonic


There are a variety of patterns which could be produced by vibrations within a string, slinky, or rope. Each pattern corresponds to vibrations which occur at a particular frequency and is known as a harmonic. The lowest possible frequency at which a string could vibrate to form a standing wave pattern is known as the fundamental frequency or the first harmonic. The second lowest frequency at which a string could vibrate is known as the second harmonic; the third lowest frequency is known as the third harmonic; and so on. The frequency associated with each harmonic is dependent upon the speed at which waves move through the medium and the wavelength of the medium. The speed at which waves move through a medium is dependent upon the properties of the medium (tension of the string, thickness of the string, material composition of the string, etc.). The wavelength of the harmonic is dependent upon the length of the string and the harmonic number (first, second, third, etc.). Variations in either the properties of the medium or the length of the medium will result in variations in the frequency at which the string will vibrate. A node is a point of no displacement. Standing wave patterns are also characterized by antipodal positions - positions along the medium that undergo maximum displacement from a high upward displacement to a high downward displacement


 Echo and Reverberation  


echo and a reverberation

Reflection of sound waves off of barriers result in some observable behaviors which you have likely experienced. If you have ever been inside of a large canyon, you have likely observed an echo This echo results from the reflection of sound off the distant canyon walls and its ultimate return to your ear. If the canyon wall is more than approximately 17 meters away from where you are standing, then the sound wave will take more than 0.1 seconds to reflect and return to you. Since the perception of a sound usually endures in memory for only 0.1 seconds, there will be a small time delay between the perception of the original sound and the perception of the reflected sound  A reverberation is perceived when the reflected sound wave reaches your ear in less than 0.1 second after the original sound wave