The Ability Of Sound To Shatter Glass Environmental Sciences Essay

There is a myth that claims that the piercing voice of the soprano vocalist has the power to shatter a wine glass. In this media-driven world, we are often shown television portrayals of such events; there is also evidence and personal testimony that supports the statement. Scientific research has also proved that sound can break a glass and the laws of physics have proven that this is possible through sound resonance.

In this extended essay, I will compare the ability of sound to shatter glass through using different sized beakers and also different shapes of glass. The significance of this experiment is to relate the physics concept with our lives. During my experimentation, three different sizes of beaker and three different shapes of glass have been utilised to test the ability of sound to shatter glass through using the laws of physics. All the beakers and glasses are made of the same glass and are of the same thickness.

The experiment is conducted by resonating the glass and beaker at its natural frequency. The glass and beaker will vibrate when sound waves are emitted to the wall of the glass. In order to shatter the glass, the amplitude of the sound is increased until the glass shatters. If lower amplitude is needed to shatter the glass, this will indicate that the glass is more easily shattered. All the three different sizes of beakers and three different shapes of glass will then be compared. . The results show that actually the smaller sized beaker is more easily shattered when compared to the bigger sized beaker; the results also demonstrate that the beaker glass is more easily shattered when compared to the wineglass, which is curved inwards and outwards at the rim.

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1.0 Introduction

1.1 SCOPE OF WORK

I have studied about sound waves and its subtopic which is resonance in Physics at High School and also during my diploma programme. .But I was disappointed to find that I couldn’t locate any literature that explores how the sound waves can shatter glass through sound resonance. This essay is an attempt to study the phenomenon that involves the factors that affect the vibration of glass through the emission of sound waves of the glass’s natural frequency

Shattering of glass can be because of many factors. Thus I set myself the objective of doing this research which is to determine whether changing the size of glass will affect the amplitude of sound needed to shatter glass. Another objective of this essay is to investigate whether changing the shape of glass will affect the amplitude of sound needed to shatter glass. Therefore, my research will be based on the two objectives. To achieve the objectives in this research I have posed two research questions which are:

Research Questions:

Does changing the size of the beaker affect the amplitude of sound needed to shatter the glass through sound resonance?

Does changing the shape of the glass affect the amplitude of sound needed to shatter the glass through sound resonance?

1.2 Background Information and Literature:

The most important thing about this essay is to know the basic information that makes the experiment related to the physics concept. In this essay the main physics concept that will be talked about is sound resonance. Using this concept, the glasses will be forced to vibrate at their respective natural frequencies until they shatter into smithereens.

There are several key terms that need to be clarified before performing the research. The first term would be the natural frequency. The natural frequency is ‘the frequency of a system which oscillates freely without the action of external force’ [1] . Another term that is important is resonance. ‘Resonance is the state which the frequency of the externally applied periodic force equals the natural frequency of the system.’ [2] .All objects have their own resonance frequency. This includes glasses.

2.0 Research Question

This extended essay will be guided by two research questions. The research questions formed were set to be the parameters of this essay.

First research question:

Research Question: Does changing the size of the beaker affect the amplitude of sound needed to shatter the glass by sound resonance?

Three beakers with different diameters of rim of glass are used to test the ability of sound waves to break the beakers.

Type of glass

Size of glass

Diameter of rim of glass, cm (±0.01cm)

Beaker A

Small

6.28

Beaker B

Medium

9.46

Beaker C

Large

11.39

Table 2.01: Size of the glass and the diameter of the rim of the glass for Beakers A and B and C

Second Research Question:

Research Question: Does changing the shape of the glass affect the amplitude of sound needed to shatter the glass by sound resonance?

Different glass can be moulded into different kinds of shape. Different shapes of glass are used to test the ability of sound waves to break the glass at its natural frequency.

Type of glass

Diameter of rim of glass/cm

Shape of the glass

Beaker A

6.28

Straight shape

Wineglass A

6.13

Curvature (inwards at the rim)

Wineglass B

6.31

Curvature (outwards at the rim)

Table 2.02: The table of the diameter of the rim of the glass, the shape of the glass for Beaker A , Wineglass A and Wineglass B.

3.0 Variables

Experiment I

Dependent: The amplitude of the sound waves needed to shatter the glass.

Independent: The size of the beaker used.

Constant: The natural frequency of the glass, the thickness, type and shape of the glass.

Experiment II

Dependent: The amplitude of the sound waves needed to shatter the glass.

Independent: The shape of the glass being used (beaker and wineglass).

Constant: The natural frequency of the glass, the thickness, type and size of the glass.

4.0 Apparatus and Materials

Apparatus

Quantity

1000ml beaker

1

600ml beaker

1

150ml beaker

1

Wineglass

1

Wineglass with outwards curvature at the rim

1

Metal spoon

1

Microphone

1

Headphones

1

Eye Goggles

1

60 Watt Speaker/Amplifier(Roland Cube 60X)

1

Cool Edit Pro 2.0 (Frequency analyzer)-laptop

1

Signal/Frequency generator(Programmable analysis software)

1

Vernier Calliper

1 In this experiment, most of the apparatus and material were available at the science laboratory. The apparatus and materials used are:

Table 4.1 – Table of list of apparatus and materials and the quantity used.

5.0 Methodology

5.1 Safety Precaution

The experiment must be done by wearing eye goggles and headset/earplugs because of the danger posed by shattering glass and due to the hazard posed by the high pitched sound.

5.2 Making a measurement for the frequency of glass

Frequency is very important in this experiment. Frequency of the glass can be determined by hearing the ‘ping’ sound produced when hitting the glass with a metal spoon. But it will only show the qualitative result which is not the actual frequency of the glass. In order to get the quantitative data for the frequency of the glass, a microphone was used and connected to a laptop so that the sound could be analyzed by using the software, ‘Cool Edit Pro 2.0’ by Syntrillium Software Corporation.

The software ‘Cool Edit Pro 2.0’ detects the sound produced by the glass and changes the sound into a Sine-wave. The wave form will be very dense and close to each other. A stable form of sine wave needs to be chosen in order to find the period for the wave. The frequency of the glass can be found by using the formula:

Where,

f = frequency of glass

T = period of glass

The frequency that measured is the frequency of the glass. Then the frequency needs to be trailed around ±100 Hz to get the actual natural frequency of the glass that can resonate the glass easily.

Experiment I and Experiment II

The steps for Experiment I and Experiment II are the same. The only difference is that for Experiment I, three beakers with a different diameter at the mouth of the glass are used. Measure the diameter of the glasses using vernier callipers and label it as Beaker A, Beaker B and Beaker C. Then, for Experiment II, three type of glass are used: a beaker, a wineglass with an inward curvature and a wineglass with an outward curvature. The glasses are labeled as Beaker A, Wineglass A and Wineglass B.

After that, for Experiment I, Beaker A is taken to start the first experiment. The frequency for Beaker A is found by using the steps as stated earlier. Roland Cube 60X, an amplifier with a built in loudspeaker which is capable of generating more than 110dB of power of sound is used to shatter the glass. Place the beaker very near to the speaker to so that it is in full contact with the glass. The frequency of the sound is generated by using a frequency signal generator. The frequency signal generator will produce sound waves with the desired frequency, generated by the Roland Cube 60X. The frequency generated will be tested on the beaker; a straw is put into the beaker to see the vibration of the beaker.

Then, the volume of the sound is increased until the beaker expands and shatters. The amplitude of sound produced by the Roland Cube 60X that caused the glass to shatter is then recorded. All the data is recorded in a table .The experiment is then repeated by using the Beaker B followed by Beaker C. All the steps for Experiment I are then repeated in Experiment II. In this experiment the glasses are changed into three different shapes of glass: Beaker A, Wineglass A and Wineglass B.

6.0 Data Collection and Processing

This section explains the data collected after the experiment was conducted. All the data was taken when tabulated into the table as shown in the table below:

Experiment 1

Type of glass

Diameter of rim of glass/cm (±0.01cm)

Frequency of the glass calculated, Hz (±1Hz)

Actual Natural Frequency of the glass,Hz (±1Hz)

Amplitude of sound needed , dB(±1dB)

Beaker A

6.28

1515

1466

123

Beaker B

9.46

689

747

128

Beaker C

11.39

625

658

130

Table 6.1: Table of Diameter of rim of glass , natural frequency, the actual natural frequency and the amplitude of the sound needed to break the beaker A,B and C

The highest frequency calculated is Beaker A, followed by Beaker B then Beaker C.

In this experiment, Beaker A only needs 123 dB to reach its elastic limit. Beaker B needs 128 dB to be broken into pieces while Beaker C is the hardest to shatter, needing 130 dB amplitude of sound to break the beaker.

Experiment 2

The data from the second experiment was tabulated in the table below.

Type of glass

Diameter of rim of glass/cm (±0.01cm)

Frequency of the glass calculated, Hz (±1Hz)

Actual Natural Frequency of the glass,Hz (±1Hz)

Amplitude of sound needed , dB(±1dB)

Beaker A

6.28

1515

1466

125

Wineglass A

6.13

1250

1153

132

Wineglass B

6.17

1449

1388

Cannot be broken

Table 6.2: Table of Diameter of rim of glass, natural frequency, the actual natural frequency and the amplitude of the sound needed to break the Beaker A, Wineglasses A and B

In this experiment, the highest natural frequency for the glasses is Beaker A. Wineglass B is the second highest followed by Wineglass A. All of the glasses are shattered at their natural frequency except for Wineglass B. Wineglass B cannot be broken, which will be explained in the discussion section of this paper.

7.0 Discussion and Analysis

7.1 How glass can be shattered

This part of extended essay will explain the actual concept of how a glass can be shattered. There are several factors that will affect the ability of sound to break a glass. The sound wave used to resonate the glass must be of a high pitch and it will start to make the object vibrate. The constructive interference occurring at the glass walls make the vibration of the glass more visible. Then the following conditions will happen:

Figure 7.1a Figure 7.1b

Figure 7.1 – Figure of an exaggerated example of the view of the rim of the glass from the top view when the sound wave is generated to the glass

In the diagram above, it shows that in figure 7.1a, there will be four nodes when the sound wave is resonated to the glass. This type of condition occurs if the frequency generated is the same as the natural frequency of the glass and the amplitude of the sound produced is high. If the amplitude is further increased, the shape of the ellipsoidal rim will increase until it reaches an elastic point until the glass shatters.

Comparatively, the diagram in figure 7.1b shows there will be six nodes produced when a higher or lower frequency than the natural frequency of the glass is used to resonate the glass. This is not the most efficient frequency for the oscillation of the glass. Thus the rim of the glass will vibrate in all directions. Below are the properties that will occur when the glass resonates:

When sound waves are generated to the wall of glass, constructive interference will occur and the glass will oscillate inwards and turn into an ellipsoidal-like shape at A as shown in the figure.

The ellipsoidal-like shape which oscillates inwards will be reflected back to its original position as it doesn’t have enough energy (amplitude of sound) to reach its elastic limit

B

The reflected oscillation of the glass will then exceed its actual rim position as it will oscillate in an ellipsoidal-like shape outwards of the actual rim shape at B.

The oscillation will continue as long as the frequency generated is the same as the natural frequency of the glass. But to exceed the elasticity limit of the glass, a higher amplitude of sound wave needs to be generated. A longer ellipsoidal-like shape will be produced. Later will exceed the elastic limit and break the glass into pieces.

Diagram 7.2- Properties of wineglass when it undergoes resonance

If a different frequency rather than its natural frequency is used, more nodes of oscillation will be produced and it is harder to break as it doesn’t reach the glass elasticity limit, as shown in diagram above. The lower number of nodes produced, the further the stretch of the oscillation will be.

7.2 The quality factor (Q-factor)

‘Q factor is a dimensionless parameter that describes how under-damped an oscillator or resonator is’ [3] . It is known that ‘Q factor is inversely proportional with damping’ [4] . The Q factor can be determined by measuring the time taken for the glass from rim to steady mode and has the highest resonance frequency. In the experiment of shattering of glass using sound resonance, the glass cannot be affected by any damping massively. ‘Damping is the decrease in the amplitude of an oscillating system’ [5] . Damping will oppose the direction of vibration of the glass so that it can reduce the glass’s vibration. Thus for shattering a glass, the glass with a high Q factor is the best as it will have less damping and higher resonance frequency.

Experiment I ( size of the beaker)

In this experiment the only difference between the beakers is the size of the beakers. It brings a difference to the amplitude of the sound wave needed to break the glass. After the experiment has been done, it becomes clear that there is a connection between the size of the beaker and the ability of the sound to break the glass.

From the result, it can be seen that smaller sized glass beaker will break more easily when sound wave of its natural frequency is directed to the wall of the glass. However, it is hard to investigate the exact math relationship between the natural frequency of the glass and the amplitude of the sound wave needed to break the glass. The high amplitude is used to expand the solid state of the glass to a more elastic shape ( liquid state characteristic) of the glass so that the intermolecular forces between the particles can be overcome.

In this experiment, the easiest glass to break by sound resonance is Beaker A as the amplitude needed to break the glass is the lowest when compared to the other beakers. This is because the beaker has a high resonance frequency. When the resonance frequency of the beaker is high, the beaker will vibrate more in a period of time. Since the glass is vibrating at a high frequency, the damping effect on the glass less effective. As small beakers will have a low damping effect, the elastic limit for the glass will also be lower. Thus less energy (amplitude of sound) needed to shatter the glass. So for the Beaker A, the size of the beaker is small, the resonance frequency is high and the damping effect is low, thus the quality factor for the glass is high. That is why lower amplitude of sound is required to shatter Beaker A

For Beaker B, higher amplitude of sound is needed to break the beaker. This because the size of the glass is bigger than Beaker A. Beaker B will have a lower resonant frequency compared to Beaker A. This is because the natural frequency of Beaker B is lower when compared to Beaker A. Thus there will be less vibration of the particles of glass per second. As the resonant frequency of the glass is lower when compared to Beaker A, the damping for Beaker B will be higher when compared to Beaker A. Therefore, the elastic limit for the glass to break will also be higher when compared to Beaker A. Since damping is inversely proportional to Q factor, thus the Q factor of Beaker B will be lower when compared to Beaker A,. Thus it will require a higher concentration of energy (amplitude of sound) to reach the four nodes mode oscillation of glass and later to exceed the elastic limit of the glass.

The hardest beaker to shatter is Beaker C. This is because the size of Beaker C is bigger than Beaker B and Beaker A. In this case, the glass with the lowest resonance frequency is Beaker C. This is because the frequency of Beaker C is very low when compared to the other two beakers. Lower frequency means a lower number of vibrations of the particles of glass per second. Thus there will be a higher damping effect for Beaker C. Damping will oppose the force of the vibration, thus making it harder for the glass to resonate. The Q factor for Beaker C is the lowest compared to Beakers B and A. Thus the amplitude needed to break Beaker C will be the highest as the beaker need more energy to reach the beaker’s elastic limit. What is needed for the glass is to have a strong resonance where it will vibrate at a higher resonant frequency, with less damping effect and a high Q factor. Then it is possible to force the beaker to vibrate with a bigger displacement and then break.

Experiment II ( Shape of the glass)

In this experiment, the most important factor that is manipulated is the shape of the glass. The shapes used in this experiment consist of shapes that have tall sides and sides with curvature. These two shapes of glass can be broken easily by sound resonance because of the structure of glass that has a certain type of periodic structure. The connection between the sound resonance and the periodic structure of the glass makes the vibration of the glass stronger. Strong vibration can reach the four nodes mode of the glass until it reaches the elastic limit of the glass.

The shape of Beaker A is with less curve and more tall sides when compared to the wine glass with curved inward or outward sides of glass. The amplitude needed to break Beaker A, Wineglass A and Wineglass B are not the same as the shape of the side wall of the glass will play a major role in the ability of sound to break the glass. When comparing all three type of glass, the glass most easily shattered is Beaker A. Having a glass with tall sides with minimum curve promotes better vibration of the glass and makes it easier to break. This is because; there will be less damping effect that will occur when using Beaker A. The tall sides with minimum curve will reduce the damping effect of the beaker. Since the damping effect for Beaker A is low, the resonance frequency of Beaker A will be high and that’s why the natural frequency of the beaker A is the highest. Since the Q factor is inversely proportional to the damping effect, thus Beaker A has the highest Q factor. That’s why lower amplitude of sound is needed to shatter the beaker when compared to Wineglasses A and B.

The curved shape of Wineglass A makes it hard for the glass to resonate at its natural frequency. Curved walls make the glass wall more suitable for damping. Due to the damping effect, the structure of the curvature in the wall can easily reshape to its actual position even though it vibrates under sound resonance. This will increase the elastic limit of the glass thus making it harder for Wineglass A to shatter. That’s why Wineglass A needs higher amplitude of sound to break the glass when compared to Beaker A. As the damping effect for Wineglass A is higher than Beaker A, thus the resonance frequency of wineglass A is lower when compared to Beaker B and the Q factor for Wineglass A is lower when compared to Beaker B. Thus Wineglass A is more resistant to being broken by sound resonance when compared to Beaker A.

In contrast, Wineglass B is different from Wineglass A and Beaker A. This is because Wineglass B cannot be shattered even though 140 decibels of sound are emitted to the glass. The shape of the wineglass itself causes it to stay rigid and it cannot be shattered. The shape of Wineglass B is curved outwards at the rim of the glass. The shape of Wineglass B makes the wineglass easier for damping. This is because, when Wineglass B is resonated at its natural frequency, it is hard for constructive interference to occur between the waves as damping occurs easily. The damping effect of Wineglass B is higher when compared to Wineglass A and Beaker A as the shape of Wineglass B is not a periodic structure. Though the natural frequency of Wineglass B is higher than Wineglass A , Wineglass B still cannot be shattered into pieces because the energy supplied to the glass is not enough to overcome the high damping effect of the glass. Thus in this experiment, glass with sides which don’t curve in too much at the top and also have tall sides of wall of the glass are most easily shattered by using sound resonance.

Conclusion and Evaluation

There are several factors that affect the shattering of glass such as the size of the glass, the shape of the glass, the thickness of the glass and also the type of glass used. In this experiment, the research concerned the question: does changing the size of the beaker affect the amplitude of sound needed to shatter the glass? After conducting the experiment, it can be seen that in Experiment I, the lowest amplitude needed to break the glass is on the smallest beaker which is Beaker A. It only needs amplitude of 123dB to shatter a glass with diameter of 6.28cm The second easiest size of glass to be broken by sound resonance is Beaker B; it only needs an amplitude of 128dB to shatter a glass with the diameter of 9.46cm. The most difficult beaker to shattered through sound is Beaker C as it needs an amplitude of 130dB to shatter a glass with diameter of 11.39cm. This answers the research question as there is a pattern to the ability of sound to shatter glass: the smaller the size of the beaker, the easier it is for the glass to be shattered as it requires lower amplitude of sound. Thus the size of glass plays an important role in determining the amplitude of sound needed to break the glass.

For the second experiment, the investigation was based on the research question of ‘does changing the shape of the glass affect the amplitude of sound needed to shatter the glass by sound resonance?’ The result from the experiment proves that the less the curvature of wall of the glass, the more easily the glass is shattered by sound resonance. In this experiment, Beaker A has the lowest curvature structure of the wall and it requires 125 dB of amplitude of sound to shatter the glass. It is followed by the Wineglass A with the wall curved inwards. Wineglass A needs a sound with amplitude of 132dB to shatter the glass. Wineglass B cannot be shattered by sound resonance. Thus the Wineglass B is the hardest to shatter by sound resonance when compared to Beaker A and Wineglass A. Thus a different shape of glass needs a different amplitude of sound to shatter it and in this experiment Beaker A is the easiest to shatter.

The method used in this research is not the most efficient way to find the amplitude of sound needed to break glass. This is because there are weaknesses and limitations to this experiment that can affect the results of the experiment. One of the weaknesses of the experiment was the calculation of the natural frequency of the glass. The natural frequency of the glass, which was calculated by using the software Cool Edit Pro, was not accurate enough. That is why to get the actual natural frequency of the glass was hard because we need to trail at about ±100Hz. This is because when recording the sound produced when the glass is hit by a metal spoon, there will invariably be a background sound recorded along with the sound from the glass. Thus this will affect the frequency of the glass calculated. Instead of using the microphone and Cool Edit Pro, another device can be used to detect the frequency of the glass: a frequency analyser.

Another weakness of the experiment was that the sound generated by the amplifier wasn’t concentrated enough upon the glass. This is because there might have been leakage of the sound energy. The size of the amplifier was very big and the sound directed to the glass was not efficient enough, thus it will have excited the glass in an inefficient way. But this can be overcome by using a compression driver. This is because the compression driver has a small diaphragm. Thus it can concentrate and direct the sound into one side of the glass wall. This way of generating sound is more efficient when compared to using Roland Cube 60X. The sound from the compression driver also needs to be generated close to the wall of the glass. To reduce the leakage of the sound, a Perspex box should be used so that all the sound energy will be concentrated upon the glass.

The biggest limitation of the research is that the apparatus that can be found in the college library makes it hard to break the glass efficiently. This is why it is hard to break the wineglass and also the beaker at its natural frequency. The apparatus that was used from the college laboratory made it impossible to perform extensive research into the experiment. That is why it is hard to break Wineglass B with the apparatus. The apparatus that can be improved is using a compression driver instead of the loudspeaker/amplifier. Other than that, instead of detecting the volume by using the amplifier, a volume meter in decibels should be used so that a more accurate measurement of the amplitude of sound can be measured.

The experiment can be extended into more in depth research by using a greater variety of sizes of glasses so that a pattern can be seen for the volume of sound needed to shatter the glass. Other than that, a greater variety of different shapes of glass also should be used so that a standard measurement of the volume of the sound needed to shatter the glass can be calculated. This experiment is important as it will explore the effect of sound resonance upon our lives. Sound resonance can vibrate any object in the world, thus this experiment has been to explore the beauty of the mechanical resonance that can distort the shape of glass.