Introduction: (Initial Observation)
Human and many animals can produce sound and use it to communicate. Many objects can also produce sound when hit or rubbed against each other. Sound produced by objects can also be used to identify the type of material used in production of that object. For example if you see a clear jar and you are wondering if it is plastic or glass, you nock on it and listen to it’s sound. Sound has many medical and industrial applications as well. Sound is used in the sea to locate and identify submarines, fishes and under water elevations. It is also being used to see inside the human body.
Although sound is a part of our daily life, we still have some questions. We hope that this set of sound related projects and their related experiments will lead us to some answers and better understanding of sound.
Galileo (early 1600s), the Italian famous for inventing the telescope, was the greatest contributor to our understanding of sound. He demonstrated that the frequency of sound was related to the perceived pitch by scraping a chisel across a brass plate causing a screech. The spacing of grooves in the scratch on the brass plate was related to the pitch.
Leonardo da Vinci (1500) discovered the wave nature of sound. Mersenne (1640) first measured the speed of sound in air. Boyle (1660) discovered that sound must travel in a medium. Newton (1660s) demonstrated the relationship between the speed of sound with the density and compressibility of a medium. Bernoulli (mid-1700s) showed that a string could vibrate at more than one frequency.
For a brief, but very useful, introduction to sound and sound waves visit Brainpop: sound where you will find a short animation with speech, so turn your speakers on, and a short quiz about sound. For another good introduction to sound visit Sound Waves at the Physics Education Laboratory at Virginia Tech.
Sound is an example of a longitudinal or compressional wave which is the physicists way of saying that it is a wave that causes a disturbance parallel to the direction in which the wave is moving, i.e., as a wave travels from left to right than the disturbance caused by that wave is in the left-right direction. Sound is a molecular disturbance and the disturbance is caused by a vibration. Whatever is vibrating, moving rapidly back and forth, sets up compressions and rarefactions which travel outwards from the object as a compressional wave. As sound waves are a disturbance or vibration in a medium of solid, liquid, or gas it follows that where there is no medium there is no sound ” . . . in space no one can hear you scream . . .”. Sound does not travel in a vacuum.
Frequencies above the 20,000 Hz level are called ultrasonic waves. You have probably heard this term used in medicine before. In fact, there is a good chance that the very first picture that your parents saw of you was a result of ultrasonic technology. Ultrasounds are used to help doctors “see” babies while still in the womb. Perhaps your parents learned whether you were a boy or a girl from an ultrasound. Ultrasound waves are also used to clean jewelry and to clean glassware in science laboratories.
A standing wave pattern is an interference phenomenon. It is formed as the result of the perfectly timed interference of two waves passing through the same medium. A standing wave pattern is not actually a wave; rather it is the pattern resulting from the presence of two waves (sometimes more) of the same frequency with different directions of travel within the same medium.
One characteristic of every standing wave pattern is that there are points along the medium which appear to be standing still. These points, sometimes described as points of no displacement, are referred to as nodes. There are other points along the medium which undergo vibrations between a large positive and large negative displacement.
These are the points which undergo the maximum displacement during each vibration cycle of the standing wave. In a sense, these points are the opposite of nodes, and so they are called antinodes. A standing wave pattern always consist of an alternating pattern of nodes and antinodes.
The nodes are produced at locations where destructive interference occurs.
More advanced information are available via the following links. Suggested experiments often exceed K12 levels.:
Some of our questions that we will investigate about in this project are:
- How sound is produced?
- What affects the pitch of sound?
- What affects the volume of sound?
- How could you measure the velocity of sound?
Each of the above questions can be subject of a different science project, but you can also combine them to make a large project.
- Collected information indicates that sound is caused by a vibration. But there are also many musical instruments that you don’t hit them or vibrate them and they make sound when you blow on them. Even we can hear sounds from seashells and empty bottles and cups without being vibrated. That tells us that sound may be produced by air movements or by the special form of material such as tubes and bottles. So the factors that may affect production of sound are vibration, air movement, structures and shapes. These are our independent variables that must be tested in our experiment. The resulted sound will be our dependent variable.
- Collected information indicates that pitch of sound is a property of sound that varies with variation in the frequency of vibration. So higher frequency results a higher sound pitch. On the other hand, we have noticed that objects made from metals usually create a higher pitch sound than objects made from wood or plastic. So the type of material may also affect the sound pitch. We want to test these two variables to find out which one has a real affect in sound pitch. Our first independent variable is the sound frequency (or frequency of vibration), our second independent variable is the type of material being vibrated. (Finally sound pitch is our dependent variable)
- Because of the wave nature of the sound, its volume may be affected by it’s amplitude or it’s frequency. So these are the variables that we will test. Since volume or loudness of sound is human perception, it may be different in different people.
- My hypothesis is that sound is the vibration itself. Such vibration at certain frequencies can be heard and identified as sound. It does not matter how does this vibration get to our ears. What maters is that such vibration eventually will vibrate our ear drum and our hearing nerves in order for us to hear a sound. I also think that musical instruments that create sound by air movement will actually vibrate air molecules, producing sound.
- My hypothesis is that objects will only vibrate at certain frequencies that depends on the material and the shape and size of that object. and that is the reason for hearing different sound pitch from different objects.
- I believe that amplitude of the sound waves are the main factor that affects sound volume, not it’s frequency.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
How sound is produced?
Introduction: The purpose of this experiment is to show that sound is made when objects vibrate. We will also show that we can lower the volume of the sound, weaken the sound waves, and reduce the duration of the sound by preventing the vibrations. You may have a device that can show the relative loudness of the sound or you may simply use your ears to estimate the level of loudness.
- Vibrate different objects (while hanged from a string or wire) and record the sound level in a table. One of these objects can be a cheap/ small trumpet or any other musical instrument who makes sound by blowing air in it. At this step we make sure that we are not causing any air movement. To vibrate these objects, hit them with a wooden spoon.
- Repeat the above experiment but this time the objects are not hanged, put them on a rubber sheet or carpet and prevent them from vibration by holding them or dipping them in water or wrapping rubber around them. You want to see what is the difference if you somehow prevent the vibration.
- Blow at the objects and record the sound.
- Blow at the objects or in the objects while preventing vibration.
|Trumpet toy||Pan||Aluminum tube||Glass Bottle|
|Hit the hanged objects||60|
|Hit the objects on rubber||6|
|Blow in while in hand||85|
|Blow in while on rubber||12|
Experiment 2: What affects the pitch of sound?
Introduction: In this experiment you will show that The faster things vibrate, the higher the pitch of the sound produced. The vibrations being more frequent mean the frequency of the wave increases. So higher pitch is caused by a higher frequency.
Part 1: Use a tape recorder/ player that can play slow, normal and fast. First we record one note of an electric synthesizer or organ. That note has a certain frequency. Then we play the tape in slow, normal and fast mode and record the results. By playing slow, we are reducing the frequency. By playing fast, we are increasing the frequency. (If you don’t have such a player, you may find a way to slow down the speed of tape being played in a walkman, just by pushing the reels or using a very weak battery). Results can be recorded in a table like this:
|Tape play mode||Slow||Normal||Fast|
Part 2: If you have a computer with sound recorder program and microphone, you can do this experiment. Most sound recorder programs have a display like an oscilloscope that shows the shape of sound waves being recorded. Keep the microphone in a close distance and hit certain objects while recording the sound by your computer. You may use a pencil and use it like a drum sick to hit the objects. Then visually compare the frequencies and record the results. When the waves are more condensed, that represents a higher frequency. Record the results in a table like this:
|Type of object||Metal tray||Card board box||plastic bottle||wood|
Experiment 3: What affects the volume of sound?
Part 1 (testing the amplitude):
We use the rubber bands to test the affect of amplitude and frequency on volume. We can also use steel wires or springs that are used for guitars to do the same test.
First build your test instrument as described here: Take a piece of wood and insert 2 nails or screws in it, about 10 inches apart. Then mount s rubber band between these two anchors.
Pull the center of rubber band about one inches and release it to get a sound. Repeat this step by pulling two inches and three inches. record the volume in a table like this:
Use numbers between 0 to 100 to represent the volume. 0 means no sound and 100 means a loud sound.
Part 2 (testing the frequency):
Adjust the tension of the rubber band and repeat the 1 inch pull experiment at 5 different tensions. record the results in a table like this.
|Tension of our string or rubber band||Volume with 1 inch starting amplitude|
|Very low tension|
|Very high tension|
Use numbers between 0 to 100 to represent the volume. 0 means no sound and 100 means a loud sound.
How could you measure the volume of sound?
Volume of sound can be measured using a decibel meter. A low cost sound meter is usually about $100.
I have not seen inside a decibel meter yet; however, this is what I think about how a decibel meter works:
A dynamic microphone gets the sound and converts it to an electrical wave or low voltage Alternative Current. This electrical wave then enters an amplifier and finally gets to a digital meter after amplification. The meter is calibrated to show a values in decibels.
Many modern audio devices are equipped with a meter or display that shows the relative volume.
A microphone attached to such devices can receive the sound and the meter will show the volume. This is a simple way for relative measurement of sound volume.
Some computer audio programs can also show the sound volume.
Materials and Equipment:
This information can be extracted from procedure or experiment section
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Visit your local library and find books related to sound or physics of sound. Review the books and list them in your bibliography. Following is a sample:
1. J. Askill, Physics of Musical Sound, Van Nostrand: New York (1979).
2. M. J. Moravcsik, Musical Sound: An Introduction to the Physics of Music, Paragon House Publishers: New York (1987).
3. J. S. Rigden, Physics and the Sound of Music, John Wiley & Sons: New York (1977).
4. T. D. Rossing, The Science of Sound, Addison Wesley Publishing Company: New York (1982).
5. H. E. White and D. H. White, Physics and Music, Holt, Rinehart, & Winston: New York (1980).
6. A. Wood, The Physics of Music, John Wiley & Sons: New York (1975).
7. J. R. Pierce, The Science of Musical Sound, Scientific American Books, W. H. Freeman: New York (1983).
8. K. D. Kryter, W. D. Wood, J. D. Miller and D. H. Eldredge, Journ. Acoustical Soc. Am. 39, 451 (1966).
9. E. A. Lacy, Handbook of Electronic Safety Procedures, Prentice- Hall: Englewood Cliffs, New Jersey (1977).
10. A. P. G. Peterson and E. E. Gross, Jr., Handbook of Noise Measurement, General Radio: Concord, Massachusetts (1963).
11. A. H. Cromer, Physics for the Life Sciences, McGraw Hill: New York (1977).
You may also include ScienceProject.com and other web resources as your references.