Physics Behind the Breaking of the Crystal Glass - Lab Report Example

Physics of Sound Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Name Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Course Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Lecture Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Date 8th march, 2012 Physics behind the breaking of the crystal glass Resonance in physics refers to the oscillation of an object at relatively high amplitude when subjected at a high frequency. The word resonance comes from a Greek word meaning resound. Without resonance, there would be no radios, television sets, musical instruments, and wristwatches. On the other hand, resonance has a negative side. Some of these disadvantages include collapsing of the bridge, helicopters flying apart (Berg 2004, pp. 87). It happens if a system can store and transfer energy between any of the storage modes i.e. potential or kinetic energy. If the energy keeps on changing from one state to another, some energy loss occur in the process. This loss is called damping. However, if the damping is infinitely small the resonance vibrates at relatively equal to the natural frequency of the object or the system. It normally occurs in all kinds of vibrations. There are several types of resonance namely; acoustic resonance, mechanical resonance, electromagnetic resonance, nuclear magnetic resonance and electron spin resonance. The kind of resonance that makes the glass to break is mechanical resonance. Mechanical kind of resonance can be defined as the affinity of any mechanical system to take in more energy if and only if the frequency of the system is the same as natural frequency of the same system. ‘If and only if’ phrase is used to mean that resonance can only occur at a certain frequency and not any other frequency. An Experiment to demonstrate how resonance occurs Apparatus Two turning fork with the same frequency Two sound boxes Metal rod Set-up Arrange the apparatus as shown in figure1 below. Procedure Mount the turning forks on the sound boxes as shown in the diagram above. Keep the two sound boxes a distance (3-4cm) apart. Hit one of the turning forks with the metal rod. Observe what happens to the other turning fork. Observation It is observed that after striking one of the turning forks, the other one started to vibrate with a relatively weaker frequency. Explanation As one turning fork is hit, the sound box which is open on one side amplifies the sound waves. Due to compressions and rarefactions produced in the air by the first turning fork, the second turning fork starts to vibrate sympathetically (William C 1987, pp. 65). This sympathetic vibration is the one called resonance. What makes the glass to break? When a crystal wine glass of radius 33mm was placed in front of speakers and a 5 Watt sound wave applied at frequency 800Hz, the glass’ rim is observed to oscillate with amplitude of 5mm. as the frequency of the sound from the speakers was thereafter increased to 140 decibels, the glass fractured. Explanation The sound wave produced by the speakers cause’s compressions and rarefactions to the air surrounding the speakers and the glass. The compressions and the rarefaction make the glass to resonant. The glass at this point cannot fracture because the resonance frequency is not equal to the natural frequency of the glass. With the increase of frequency of the speakers the relative resonance frequency of the glass increases. At the fracture point, the resonance frequency was the same as the natural frequency of the glass hence the fracture. When the natural frequency equals the resonance frequency of the system, the potential energy changes to kinetic energy hence the fracture. The amplitude at this breakage point is at its highest. The workings of the human larynx Human larynx works as a result of forced vibration as the air moves out from the lung and is forced by the larynx muscles to give the required pitch. The contraction and relaxation of the larynx muscle determines the frequency variation. In human larynx the way the vibrating parties interact between mass, length and tension and their effects is a complex phenomenon. As the larynx vibrates it makes the speech sound to be audible. The forced vibration by the larynx set up pulses which are closely triangular from which the amplitude, waveform and fundamental frequency are modified by the larynx muscles. How Forced vibration works is demonstrated in the following explanation. Explanation If a turning fork is hit with a metal rod, it starts to vibrate at its fundamental frequency and at low-order harmonics which depends upon the length, thickness and the material of the turning forking used. If the turning fork is hit and then pressed on the table top, the tone of the turning fork becomes louder. This is because the turning fork makes the table to vibrate at the same frequency. But the table has a larger vibrating area than the turning fork hence a more intense sound. Take an example with a violin string vibrating between two clamps; it produces a sound of low intensity. If a bridge is place across the string, it is forced by the string to vibrate (sympathetic vibration) which makes the intensity of the sound to increase. This is how the larynx works in humans. Comparison between the physics of the breaking glass and the workings of the human larynx The physics behind breaking of the glass was discussed, and it was concluded the fracture is as a result of sympathetic resonance. Again, the working of human was also discussed at the conclusion was that it is as a result of forced vibrations (Borg nd, pp. 1). So, how do the two compare? In resonance systems vibrates at larger amplitudes at some frequency than in other. Forced vibration occurs when an alternating force is applied to a system (mechanical). Therefore, the working of the human larynx and the physics of breaking of the glass compares because they both happen due to the resonance. If say, the glass is made to resonant and then touched, it will break even before the natural frequency is attained. The two phenomena depend highly on relative intensity in decibels of the original source of the sound. If for instance the intensity of the original sound is not high enough then, the glass would not break and similarly if the sound produced by the larynx will be of low quality. Without damping the glass can break even when the original sound source has the same frequency as the glass. But due to damping which happens result of loss in the process of travel the original intensity of vibration must be the greater than the natural frequency of the glass. In other words, as the sound move from one point to another it losses some energy. In conclusion to the comparison, if one makes a turning fork to resonant and then you touch it with a finger, the finger will vibrate with the frequency of the turning fork. This is the same effect which larynx in the voice box uses. Mathematics behind the two phenomena Resonance and the sound intensity is highly determined by three factors namely; the tension, the mass, and the length. Sound wave velocity can be calculated using the following mathematical formulae. Force multiplied by length divided by mass V=FL÷M (m/s) The intensity and the loudness of a sound wave propagated through air or through other carrying medium carry energy outward from a source to a detector (Borg nd, pp. 3). In our case the glass is the detector. The intensity level is the level at which the energy is transported by the sound wave in power per unit cross-section area. It is meanly measured in decibels. Therefore relative intensity (β) is given by; β= 10 log (I÷I0) Bibliography Berg R. E. 2004. The Physics of Sound. San Francisco: Benjamin Cummings. Borg X. nd. How you can make a wine glass sing [online] at: http://recipes.howstuffworks.com/question603.htm Retrieved on 8th march 2012 Stanley R. W. 1987. College Physics. New York: Harcourt brace Jovanovich College Publishers. Hogan J. nd. Tacoma Narrows Bridge Disaster [online] at: http://www.enm.bris.ac.uk/research/nonlinear/tacoma/tacoma.html#mpeg Borg X. nd .The Glass shattering experiment Weakening glass' intermolecular structure [online] at: http://ww.blazelabs.com/f-p-glass.asp Retrieved on 8th march 2012 William C. Elmore W. C., Mark A & Heald A. 1985. Physics of Waves. New York: Dover Publications Read More