Sound
Page
I.Naive Ideas Concerning Sound...... 3
II.Sound Production – Constructing Sound Devices
A. Viewing Sound...... 4
B. Clucking Chicken...... 5
C. Film-A-Horn?...... 6
D. How Do We Hear? ...... 7
E. How Is Sound Produced?...... 8
F. Extras - Production?...... 10
III.Building a Model Using the Characteristics Of Sound
A. How Does Sound Travel?
1. Does Sound Travel Through A Vacuum? (Demo)...... 12
2. Do Solids Conduct Sound Better Than Air? (Activity)...... 13
3. Do Liquids Conduct Sound Better Than Air? (Activity)...... 15
4. The Speed of Sound In Various Substances...... 16
5. Extras - Transmitting Mediums?...... 17
B. Illustrating the Model Of Sound
1. FUNdamentals of Sound...... 20
2. What is a Sound Wave? ( Frequency, Pitch, Wavelength Using A Slinky)...... 21
a. What Causes High And Low Pitched Sounds?...... 25
b. Constructive and Destructive Interference
c. Changing Pitch And A Moving Sound Source? (Doppler Effect)..... 29
3. Loudness, Energy and Amplitude Using A Slinky...... 33
4. Check Your Understanding of the Model ...... 34
5. Extras - The Model...... 35
C. Resonance (One Vibrating Object Causes Another to Vibrate)
1. Two Ways That One Vibrating Object Can Cause Another To Vibrate? ... 39
2. Resonating Bar...... 41
IV.Applying The Model of Sound
A. Using Goldwave to Analyze Sound...... 42
B. Using Goldwave to Determine the Frequency of an Unknown Sound...... 46
C. How Does A Record Produce Sound? (Name That Sound)...... 47
D.Outstanding Demonstrations By Workshop Participants
E. Extras - Applications...... 49
V.Vendor List ...... 51
VI.Bibliography ...... 52
Sound
Page
I. Naive Ideas Concerning Sound...... 3
II. Sound Production - Constructing Sound Devices
- Viewing Sound...... 4
- Clucking Chicken ...... 5
- Film-A-Hon?...... 6
D. How Do We Hear? ...... 7
- How Is Sound Produced? ...... 8
- Extras - Production? ...... 10
III. Building a Model Using the Characteristics Of Sound
A. How Does Sound Travel?
- Does Sound Travel Through A Vacuum? (Demo) ...... 12
- Do Solids Conduct Sound Better Than Air? (Activity)...... 13
- Do Liquids Conduct Sound Better Than Air? (Activity)...... 15
- The Speed of Sound In Various Substances ...... 16
- Extras - Transmitting Mediums? ...... 17
B. Illustrating the Model Of Sound
1. FUNdamentals of Sound ...... 20
2. What is a Sound Wave? ( Frequency, Pitch, Wavelength Using A Slinky) ....21
- What Causes High And Low Pitched Sounds? ...... 25
- Constructive and Destructive Interference
- Changing Pitch And A Moving Sound Source? (Doppler Effect)...... 29
3. Loudness, Energy and Amplitude Using A Slinky ...... 33
4. Check Your Understanding of the Model ...... 34
5. Extras - The Model ...... 35
C. Resonance (One Vibrating Object Causes Another To Vibrate)
- Two Ways That One Vibrating Object Can Cause Another To Vibrate? ...... 39
- Resonating Bar ...... 41
IV. Applying The Model of Sound
- Speed of sound in a Parking Lot...... 45
- Using Goldwave to Analyze Sound ...... 46
- Using Goldwave to Determine the Frequency of An Unknown Sound ...... 50
- How Does A Record Produce Sound? (Name That Sound) ...... 51
- Outstanding Demonstrations By Workshop Participants
- Extras - Applications ...... 53
V. Vendor List...... 51
VI. Bibliography...... 52
I. Naive Ideas Concerning Sound
1.Sounds can be produced without using any material objects.
2.Hitting objects harder changes the pitch of the sound produced.
3.Sound waves are transverse waves that travel in exactly the same way water and light waves travel.
4.When waves move through a body of water the water is actually moving from one point to another.
5.When waves interact with a solid surface, the waves are destroyed.
6.Loudness and pitch of sounds is the same thing.
7.You can see and hear a distinct event at the same moment.
8.Sounds can travel through empty space (a vacuum).
9.The sound of a train whistle changes as the train moves by because the engineer purposely changes the pitch of sound.
10.In wind instruments, the instrument itself vibrates, not the internal air column.
11.Music is strictly an art form; it has nothing to do with science.
12.In actual telephones (as opposed to tin can telephones) sounds, rather than electrical impulses, are carried through the wires.
13.Ultrasounds are extremely loud sounds.
14.Megaphones create sound.
15.Noise pollution is annoying, but it is essentially harmless.
II.Sound Production
An age old question asks: If a tree falls in a forest where there is no one to hear it, does it make a sound? To answer this question, the phenomena of sound must be defined. In the physiological sense, there are three requirements for sound:
1. A source of energy,
2. A transmitting medium for the energy,
3. A receiver to receive and decode the energy.
In the physical sense, sound is a series of energy disturbances in a material medium, not necessarily requiring a receiver or observer. Therefore, the answer to the above question depends on the definition used. In this topic, "sound" will be interpreted in its physical sense.
Sound may be specifically defined as a mechanical vibration in a material medium (solid, liquid, gas) within a frequency range approximately between 20 vibrations/sec and 20,000 vibrations /sec. These frequencies are capable of affecting the human ear (providing that its intensity is between 0 db and 120 db). Waves of frequencies lower than 20 vib/sec. are called infrasonic, and those of frequencies higher than 20,000 vib./sec. are known as ultrasonic.
Viewing Sound – A Simple Oscilloscope
The source of every sound is a vibrating body. An oscilloscope is an expensive electronic instrument that can graphically display the patterns of sound vibrations on a video screen. We can think of an oscilloscope as a device which enables us to see sound. This activity allows one to make a simple device that produces visual vibration patterns produced by sound.
Many scientific measuring instruments have dials with pointers to indicate the magnitudes of the measurements. A pointer is actually a lever that magnifies the distance that the instrument moves. Unfortunately, pointers have mass which the instrument must move. In very sensitive instruments this presents a problem, since the force that the instrument measure is too weak to move the mass of the pointer. The solution to the problem is a mass less pointer---a beam of light referred to as a light lever! A small mirror is attached to the instrument. A beam of light is reflected off the mirror onto a screen that may be several meters distant. The beam is, in effect, a mass less lever several meters long that greatly magnifies a very small movement of the instrument.
Construction:
Remove both ends of a small steel can such as a soup, nut or single serving juice can. Cut the bottom two thirds of a large round balloon. Stretch the bottom, of the balloon, over one end of the can and attach it securely (see diagram).
Use double-sided tape to fasten a small (.5 cm) mirror to the rubber midway between the center and the edge. Plastic mirror is best; many stores sell plastic mirrors for students to stick up in their lockers. These mirrors can be cut with a hacksaw or broken into small pieces with pliers (Wear Goggles). The advantage of plastic mirror is that it does not have dangerous sharp edges..
Clucking Chicken
Background: When something with a small surface like a string vibrates, it pushes a very small mass of air, resulting in a sound that is not very loud. But if the string is attached to a larger surface, forcing it to vibrate at the same frequencies as the string, the larger surface will push a larger mass of air, resulting in a louder sound. Physicists very sensibly refer to this phenomenon as forced vibration. Please understand that this is not resonance. Resonance is a special case of forced vibration in which a body is induced to vibrate at its natural frequency. Every object has one or more frequencies at which it will naturally vibrate. In this activity we will force the bottom of a plastic cup to vibrate at frequencies which are natural to a string but not to the cup bottom.
Construction: Make a small hole in the bottom of a metal can or plastic cup. Tie a small paper clip on one end of a sturdy cotton string about 70 cm long, and run the other end through the hole in the bottom of the cup (see diagram). Tie a small piece of cellulose sponge at the other end of the string. (The rectangular sponges commonly sold at supermarkets are made of cellulose.)
Procedure: Dip the sponge in water and squeeze it so that it is damp, not soggy. Hold the cup securely in one hand. With the other hand fold the sponge in half, and use it to grasp the upper part of the string tightly. While maintaining a tight grip, slide the sponge down the string with short jerking motions. The sound produced will resemble a loud, raucous chicken. By varying the manner in which the sponge is slid down the string, the sound can be made to resemble a frog or what might politely be called “rude noise.” Some students enjoy decorating their creations with felt scraps and doll eyes to resemble chicken or frog heads.
Explanation: Wetting the sponge adjusts the friction between it and the string to a level where it sticks and slips in rapid succession. This sets up an irregular mixture of vibrations in the string. Irregular vibrations result in what is commonly called noise what most people consider music results from regular vibrations. The string forces the cup bottom to vibrate at the same frequencies, thus amplifying the sound.
Further Investigation: Instead of attaching a cotton string to the cup, try various cords, wires and ribbons, or strings from violins or guitars. Instead of a damp sponge, try leather or cloth coated with beeswax or rosin. What if the string is attached to the inside of the cup instead of to the outside? Attach a spring, elastic or chain of rubber bands to the cup and pluck it. Attach a stretched wire coat hanger and bang it with a hard object. What happens if you use larger containers such as a restaurant size food can or a garbage can?
Film-a-Horn:
The observation of how a Stadium horn was constructed gave rise to this inexpensive "LOUD" horn. This simple "make and take" horn will provide a high interest teaching tool for the fundamentals of sound.
Materials:
Film canister, single hole paper punch, 3/4" punch, 1" inch punch, thin plastic from a shopping bag, 4" length of 1/2" diameter PVC pipe, 3/8" bit and drill (the punches can be purchased from a hardware store)
Preparing The Materials:
1.Using the 3/4" punch; make a hole in the bottom of the 35 mm plastic film canister. To accomplish this, make sure that you set the film canister on a cutting board, place the punch on the inside of the canister, and then hit the punch with a hammer.
2.Using a single hole paper punch, punch a hole in the middle of the side of the film canister. This will become the hole that you blow into.
3.Take the cap of the film canister and punch out the center of the cap, using the 1" hole punch. This hole can also be punched out by using a piece of one-inch metal pipe.
4.Obtain a 4" long piece of 1/2 inch PVC pipe. Drill a 3/8" hole in the PVC pipe about one inch from the end of the pipe.
Assembling The Film-a-Horn
1.Insert the 1/2" PVC pipe into the 3/4" hole from the bottom of the canister. Push the PVC pipe into the film canister so that it is approximately 1/2 way into the film canister.
2.Place the cover of the film canister on the table so that the cover can be snapped onto the canister containing the PVC pipe.
3.Obtain about a 2" square piece of a plastic grocery bag and place it on top of the film canister cover.
4.Push the canister containing the PVC pipe into the plastic covered top. Once inserted the excess plastic can be trimmed off.
5.Slide the PVC pipe forward until it lightly touches the piece of the plastic grocery bag (membrane).
Note:You will know that you have done a good job if the plastic looks smooth and tight like a drumhead.
Using The Film-a-Horn
Test by blowing into the hole in the canister and moving the tube until a rich full sound is heard.
Experiment Modification
Try different types of plastic instead of the thin plastic grocery bags. Suggestions were made to try a piece of zip lock bag, a 2 mm plastic garbage bag, wax paper, aluminum foil or different types of plastic wrap. Try using a piece of 8" PVC pipe and drilling holes approximately 1" apart. This will make quite a musical instrument.
How Do We Hear?
The human ear is an extremely good detector of sound. Even the best microphones can barely match the human ears sensitivity to sound. The function of the ear is to change the vibrational energy of sound waves into electrical signals that are carried to the brain by way of nerves.
The sketch above indicates the structure of the human ear. Sound enters the passageway of the outer ear arid strikes the Tympanum, or eardrum, causing it to vibrate. Inside the eardrum, there are three tiny bones, the hammer, the anvil, and the stirrup. These bones conduct the vibrations to the liquid-filled cochlea in the inner ear that transform the sound energy into electrical impulses that are sent to the brain.
At the entrance to the cochlea is the oval window. The amount of energy in the sound wave determines the amount of pressure that is exerted on the oval window, and the intensity of the sound that is heard.
Inside the cochlea is a fluid contained by a membrane that contains over 30,O0O nerve endings. This membrane becomes gradually thicker and less taut through the cochlea. The thicker, less taut end is more sensitive to slower vibrations (low frequencies of sound), while the thinner, tighter end is more sensitive to rapid vibrations (higher frequencies of sound). This is analogous to a thick loose rubber band that would have vibrated slowly compared to a thin, tightly stretched rubber band that would vibrate more rapidly. Thus, the rate of vibration, or frequency, of the sound wave determines the part of the membrane and corresponding nerves, which will be stimulated. This is the mechanism by which the human ear is able to distinguish sounds that vary in their frequency of vibration. Our perception of the highness or lowness of these frequencies is called pitch.
The human ear cannot hear all frequencies of sound waves. For example, you cannot hear Sound from a person waving his hand back and forth, although the person is alternately compressing and rarefying air molecules around their hand. By the scientist’s definition Sound is being produced. The range of frequencies of sound, which can be detected by the human ear, known as the human range of audibility, varies from individual to individual but is typically between 20 and 20,000 hertz. This means that the lowest pitch sound which humans can hear is produced by a source vibrating about 20 times per second, and the highest pitch sound is produced from a source vibrating at about 20,000 times per second. Sounds produced from sources vibrating more rapidly than this are known as ultrasounds. As one ages, the membrane in the cochlea becomes brittle and the range of audibility decreases, especially in the region of higher frequencies.
How Is Sound Produced?
Materials: Glass Of Water Tuning Fork Rubber Band
Idea: Sounds can be produced by various means.
Process Skills: Describe, Experiment, Listen, Observe, Explain
Duration: 30-min., (15-20 Min. (U)
Student Background:
For the lower grades, this activity is to allow students a chance to experiment with making different sounds. For upper level grades students may quickly cover the procedure as a background for the next activities.
Advance Preparation:
Try the activity before the students do it. Individuals should be divided into groups of 2 or 3 with a ruler, tuning fork, a glass of water, and rubber bands for each group.
Management Tips:
Important: Handling Of Tuning Forks
Tuning forks can be ruined if hit against any hard surface, such as table tops, metal objects. Etc. Use the heel of your shoe, a rubber mallet or a rubber stopper.
The Activity
1.Stretch a rubber band and pluck it with your finger. Can you see the rubber band vibrate? Can you feel the vibrations of the rubber band on your finger?
2.Now stretch the rubber band tighter and pluck it. Do you hear a change in sound? What change do you notice in the vibrations of the rubber band?
3.Try stretching the rubber band as much as you can, pluck it, and notice the sound and the vibrations of the rubber band. What do you notice?
4.Strike a tuning fork against a hard covered book. Do you see movement in the prongs of the tuning fork? What is this movement called?
5.Strike the tuning fork again and quickly put the prongs into a glass of water. What do you notice that happens to the water? Can you explain this?
6.Can you think of another experiment you can do to show the vibration of sound? EXPLAIN.
7.Make a general statement about what you have learned from the ruler, tuning fork, and rubber band related to this activity.
How Is Sound Produced? Cont.
Points To Emphasize In The Summary Discussion:
1.(2)Yes you can see and feel the rubber band vibrate.
2.(3)More vibrations. As the rubber band is stretched more, the pitch goes up.
3.(4)The tighter rubber band vibrates faster and makes a higher pitched sound.
4.(5)The motion is called vibration.
5.(7)It ripples. Vibrations are transferred to the water. The metal of the tuning fork moves back and forth and splashes the water.
Emphasize that sound is produced by vibrating objects.
Possible Extensions:
The vibrations of the tuning fork can be observed by striking a tuning fork and touching it to a ping-pong ball hanging by a thread. The ball will move out and back and out again as ft is hit by the vibrating prong.