ScienceScene Home Page
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
A. Viewing Sound 4
B. Clucking Chicken 5
C. Film-A-Hon? 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. Speed of sound in a Parking Lot 45
B. Using Goldwave to Analyze Sound 46
C. Using Goldwave to Determine the Frequency of An Unknown Sound 50
D. How Does A Record Produce Sound? (Name That Sound) 51
E. Outstanding Demonstrations By Workshop Participants
F. 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.
Extras – Sound Production
The Ruler
Materials: A ruler, table
Lay the ruler on the table and hold down one end of it with your hand. With the other hand bend the ruler and let go quickly. The ruler vibrates up and down and you hear a sound. Whenever anything vibrates hard enough and fast enough it sets up vibrations in the air which strike your ear and you hear a sound. That’s how all sounds are made. Something somewhere is moving back and forth hard and fast enough to send out vibrations to your ear.
Move the hand holding the ruler to the table back and forth with the ruler and vibrate the other end. When a short piece of ruler is over the edge of the table you can see it vibrate fast and hear a high-pitched sound. When you move the ruler further over the edge you will see it vibrate more slowly.
The Table fork
Rap the tines (the fingers) of the fork against something hard (not the furniture; you’ll mar it; use an old piece of wood). The tines of the fork will vibrate, producing a musical note. It’s not very loud, so you’ll have to hold it up close to your ear to hear it.
Making Sound With a Comb
The pitch of a note depends on the number of vibrations per second. The greater the number of vibrations the higher the pitch will be.
A. Puppy whine: Find a book with a cloth cover and draw the corner of an envelope, postcard, or playing card rapidly across the grain of the cloth. You will hear a shrill note of high pitch. Produce a rapid series of shrill notes resembling a puppy whining. You can produce a similar effect by running tile finger nails of one band across tile grate.
B. Quack-quack: Repeat part A with the coarse teeth of a comb and vary the speed and timing until you get a “quack-quack” sound.
C. Siren: The harder you blow into this whistle the higher and higher the pitch of the note it produces. It is a fire engine siren on a small scale.
Sound through a solid
One way to show that solids transmit sound is to have students hold one ear against the desk and cover the other ear with a hand while a student or the teacher holds a vibrating tuning fork against the surface of the desk. In another method, use a long stick or beam instead of the table.
Paper Noise
Materials: Two sheets of paper of paper
Eves- see someone split a wide blade of grass, hold it between their thumbs and blow a squeaky sound? You can make this same sound a lot easier with two sheets of paper.
Hold the two sheets of paper so that one edge over-laps the other slightly and blow between the papers. The force of the air going between the sheets will set them to vibrating fast enough to make a squeaky, silly sound.
Extras – Sound Production cont.
Listening to the World Around You
Materials: your ears, timer, pencil, sheet of paper
Procedure
1. Sit down, close your eyes, and try to notice sounds. Remain still for at least 2 minutes, and try to identify each sound you hear.
If you are outdoors, listen for little sounds, like the wind in the trees, chirping birds, or footsteps. Listen for bigger sounds, too—cars being started, planes flying overhead, sirens wailing, horns honking, people talking. If you are indoors, you might hear a radiator clanking, a clock ticking, a radio or television playing or a baby crying.
2. After about 2 minutes, open your eyes. Now, list all the sounds you heard. How many did you list? If you like, try to notice sounds with a friend, and compare notes. Did she hear something you didn’t hear?
3. Organize your list of sounds into categories, or groups of like things. For example, how many musical sounds did you hear? How many engines? How many voices? Did you hear other groups of sounds?
Feel The Voice.
Materials: none
Procedure:
Feel various parts of the throat while humming. You can feel strong vibrations when you touch the area of the vocal cords.
Comment:
The voice is produced as air passes through the vocal cords In a particular way. Animal sounds differ from one another because of the difference in the structure of their vocal cords.
Big Bang
Materials: A paper bag.
Procedure:
Fill the bag with air. Crush It quickly between the hands, and listen for the “bang.”
What happens:
As the hands come together, the air in the bag is compressed quickly. The sound is heard as the compressed air is released and assumes regular atmospheric pressure.
The Humming comb:
1. Lay the wax paper on one side of the comb and hold them together at both ends.
2. With your lips slightly open, gently press your mouth on the other side of the comb. Talk through the teeth of the comb. Try humming a song
III. Building A Model Of Sound - Transmitting Mediums
Does sound travel through a vacuum? (Demonstration)
Materials: 2 flasks, 2 rubber stoppers, 2 small bells on a stiff wire, Bunsen burner or hot plate
Students need to understand that sound is produced by vibrating objects and that as the object moves back and forth, the sound travels out from the object.
The bell will be able to be heard inside the flask at the beginning of this demonstration because there is air in the flask. Some water is then put into the flask and the flask is heated until the water boils for about a minute. The boiling forces air out of the flask because steam is produced which fills the flask. When the flask cools, the steam condenses back to water. The bell is much fainter in sound in this partially evacuated flask.
Try the following procedures before demonstrating them to your class.
1. Attach a small bell to each wire and place the other end of each wire in the rubber stoppers. Adjust the wires so that each bell will hang in the center of its flask when closed.
2. Close the flasks. Shake the flasks and have the students listen to the bells.
3. Take the stopper off of one flask. Cover the bottom of the flask with water and carefully heat it over a Bunsen burner until boiling. Let the water boil for a minute or so, turn off the
4. Let the flask cool for a minute, shake it. And try to hear the bell. Shake the unheated flask in the same way and have the students compare the sound.
5. Ask the following questions:
a. Why did you no longer hear the bell ring in the sealed flask where the water was boiled?
b. Why was the water boiled in the flask?
c. Can you make a general statement about sound traveling through a vacuum?
d. Why do you think sound cannot travel through a vacuum?
e. Is it reasonable to be able to hear rocket exhaust or Star War sounds in outer space? EXPLAIN.
Answers
a. Because there was less air in the flask
b. To create a partial vacuum by driving out the air
c. Sound does not travel through a vacuum. Sound needs a medium through which to travel
d. Sound needs a medium to carry the vibrations
e. No. Sound waves do not move through empty space so you could not hear rocket exhaust or Star Wars sounds in outer space
During discussion, emphasize that:
Sound does not travel in a vacuum.
Sound waves need a medium through which to travel.
The vibrations produced by vibrating objects require a medium through which to travel.
The Sound waves hit the eardrum that vibrates in response.
Light waves are a different variety of waves than sound waves.
Light waves do not need a medium through which to travel--they can travel through a vacuum.
To extend this demonstration, you could, if possible, procure a vacuum pump and evacuate a bottle with a bell in it. The bell will not sound when shaken. As the air is slowly allowed to enter the jar, the bell begins to be heard.
Do solids conduct sound better than air?
Materials: metal coat hanger, spoon. Thin wire, nylon fish line
1. Tie the center of a 1 meter length of string to the hook of a coat hanger.
2. PREDICT what will happen if you dangle the coat hanger on the string and hit it against the table.
3. Try hitting the coat hanger against the table. What do you OBSERVE about the result of the sound?
4. Now, PREDICT what result you will OBSERVE when you hold the ends of the string in your ears as you repeat the activity.
5. Try it. How do the sounds COMPARE when the ends of the string are held in your ears and when you did the same experiment without the string in your ears?
6. EXPLAIN what causes the sounds to be different.
7. Does air or the solid string conduct Sound better?
8. COMPARE metal wire, string and nylon fishing line as conductors of sound. First, PREDICT which one will be the best and worst conductor, then tie each of the conductors to the coat hanger in turn and listen to how well the materials conduct sound from the clanging coat hanger to your ears.
|Conductor Test |Predict - Best and Worst |Record Results |
|String | | |
|Thin Wire | | |
|Nylon Fish Line | | |
| | | |
Do Solids Conduct Sound Better Than Air? Cont.
Idea: Sounds travel better through solids than through liquids or gases.
Process skills:
Observe
Compare
Predict
Test
Duration: 20 min.
Background:
Students need to know that sounds are made by vibrating objects and that they move as vibrations through matter.
Advance Preparation:
Collect the needed materials.
Students may work in pairs or in larger groups. They can pass the coat hanger string setups around and share them. In the classroom, be sure students don’t hit the coat hangers together and have the activity degenerate into a jousting match.
Management Tips:
Other objects, such as spoons, rulers or metal utensils may be substituted for the coat hangers.
Note a common naive conception among children is that air conducts sound better than solids or liquids. This activity provides a dramatic experience demonstrating superior sound conductivity of solid materials as compared to air.
Responses To Some Questions
1. Try to be sure that students understand the key comparison being made here.
2. Predictions should be verified.
3. It will make a clunking sound. The sound will not be very loud or very pleasant.
4. Many students may expect the sound to be less in volume since their ears are being plugged with their fingers.
5. The sounds are now louder and more musically pleasant. The coat hangers sound like chimes now.
6. The sound is conducted directly from the coat hanger through the solid string. More of the sound reaches your ears than when it travels through the air to your ears.
Points To Emphasize
7. Solid string.
8. Prediction answers will vary among the students. Results will depend on the actual materials experimented with. Thickness and tautness of conducting materials may be factors, as well as the densities of the conducting materials.
Be sure to emphasize that the major variable being investigated here is a comparison between movement of sound through air as compared to movement through a solid. Emphasize that denser media transmit sounds better than less dense media.
The Summary Discussion:
Try comparing longer and shorter strings. Try the activity with the coat hanger suspended from a long rubber band (little sound is transmitted because the flexible rubber band absorbs most of it and converts it into heat).
Possible Extensions:
Students may be encouraged to do some reading to discover why different substances behave differently.
Do Liquids Conduct Sound Better than Air?
Have a friend take two stones into the water some distance from you. Have him bang them together in the air, and see how loud the sound is. Then have him place the stones underwater, and bang them together while your head is underwater. The sound will be much louder.
Here’s why:
Sound exists in the form of waves, and the waves travel better in water than in air. (Solids carry sound better than air as a rule. American Indians are said to have listened for distant hoof beats by placing an ear to the ground
Speed Of Sound In Various Substances
The speed of sound in the air is about 330 meter/second at 0o C. As the temperature of the air rises, the speed of sound increases, at a rate of about 0.6 meter/second for each Co. The formula or relationship can be stated as:
VT = 330 m/sec. + (.6 m/sec. 0C x T)
(VT is the velocity of sound at room temperature, and T is the existing room temperature.)
If the temperature was 19o C then the speed of sound would be:
330 m/sec. + (.6 m/sec. 0C x 19o) or 341.4 m/sec.
In a liquid such as water the speed of sound at 19o C is 1461 meters/second approximately four to five times faster than air. In some solids, the speed of sound is even greater, for example: in iron, sound may travel 5,000 meter/second, about 15 times faster than air. The speed of sound in various substances can be seen in the following chart.
VELOCITY OF SOUND IN VARIOUS SUBSTANCES
Substance temp Co m/sec ft/sec
Solids
Aluminum - 5,094 16,704
Copper 100 3,290 10,800
Copper 200 2,950 9,690
Iron and soft steel - 5,000 16,410
Nickel - 4,973 1,632
Liquids
Alcohol 20.5 1,213 3,890
Benzene 0 1,166 3,826
NaC1 10% solution 15 1,470 4,823
NaC1 20% solution 15 1,650 5,414
Water 13 1,435 4,708
Gases
Air 0 330 1,089
Carbon Dioxide 0 258 846
Hydrogen 0 1,268 4,160
Oxygen 0 317.2 1,041
Extras - Transmitting Mediums
Hear through your teeth
Set a fork or a tuning fork into vibration. Wait until you cannot hear any sound from the fork, then place the handle between your teeth. The sound will still be heard. Repeat the experiment by placing the handle on the bone at the back of your ear.
Experiment
Materials: String, A knife, A fork, A spoon
Attach whatever you want to listen to the middle of the string. What you hear depends on what you vibrate. What you hear in the tin can in the next experiment depends on what your friends say into another tin can in the next room.
Liquids carry sound
Place your head under a pool of water so that your ears are immersed. (It may be in a swimming pool, the sea, a river or even a bath tub.) Let somebody else strike a gong or a bell under the water away from you, while your ears are still under water. You will hear the sound coming through the water clearly. It is a fact that sound travels about four times as fast under water as through air.
Sound through a liquid. Some students may have heard rocks banged together under water. Insert the stem of a tuning fork into a hole bored into a large cork. Set the tuning fork in vibration and hold it so that the tuning fork rests on the surface of water in a container standing on a resonating box. Students will hear the vibrations of the tuning fork transmitted from the cork through the water and into the air of the room.
Sound Travels Through Solids
A. Place your ear against one edge of a table while a companion scratches the opposite edge lightly. You will hear the sound distinctly.
B. Hold one end of a pencil in your teeth while you scratch the other end lightly. You will hear the sound distinctly.
C. On a railroad track, go at least a quarter of a mile away from a companion and strike a rail with a heavy rock. Then reverse your roles. You will hear two sounds, one through the rails and the other, a little later, through the air.
To Make and Use a String Telephone
A. Punch a small nail hole in the middle of the bottom of each of two empty food cans, and connect the cans with a long string knotted inside each can.
Go far enough apart to stretch the string and talk into one can while a second experimenter listens in the other, with his uncovered ear closed by a finger. Then exchange roles. You will each hear the other distinctly. Remember, the string must be stretched.
B. Use paper drinking cups instead of the tin cans, and tie each end of the string to a matchstick 3/4-inch long, inside a cup. Stretch the string and make the test. You will hear each other very, very distinctly.
Extras - Transmitting Mediums cont.
Tin Can Sound
Materials: Two tin cans, A long length of cotton string
Punch a small hole in the exact center of the bottom of each tin can. Thread one end of the string through the bottom of one of the cans and out through the top. Tie a knot bulky enough to prevent the string from being pulled back out through the hole.
Thread the other end of the string through the hole in the other can. Have a friend take the can with the knot in it into the other room, keeping the string straight. When he is as far away as he can get and still keep the string straight, pull the string through the hole in your can, cut if off and tie a knot in the end. When both of you hold your tin cans up to your mouths or ears (depending on who’s talking and who’s listening), and keep the string between the cans fairly tight, you’ll be able to talk back and forth because you’ve made a tin-can telephone.
To Make and Use an Air Telephone
Roll a long strip of wrapping paper into a tube about 1-in. in diameter and tie it
Listen at one end of the tube while a companion whispers as gently as he can into the other end.
You will be surprised at how distinctly you hear the sounds.
Try this experiment also with a long piece of empty garden hose or metal pipe.
Transmitting Sounds Through a Table
Materials: Table, fork, Drinking glass, Table
Announce to your friends that you can carry sound in your finger tips. Rap the fork against a block of wood and touch the handle with your finger tip. With your eyes on your finger tip—and your friend’s eyes too—slowly bring it to the edge of the glass. As you touch the glass, also (without your friends noticing it), touch the handle of the fork to the table. Your friends will hear a musical note that seems to come from the glass!
You know, of course, you haven’t carried sound in your finger tips at all because it came from the vibrating fork. Why did the fork sound so loud when you touched the handle to the table?
Here’s the science secret: when only the tines of the table fork vibrate they set into motion only small quantities of air. That means the vibrations in the air are too weak for you to hear unless you hold the fork close to your ear. But when you touch the handle of the fork to the top of the table the vibrating fork sets the whole table vibrating. With such a large surface moving back and forth a lot more air is set into motion and the resulting louder sound is easier for you to hear.
Tapping codes through water pipes
Send a code message made up by a pupil and yourself through a water pipe that goes from one room to another on the same floor or on different floors. By striking the water pipe with a piece of iron in one room the sound reaches your pupil in the other. Then interchange messages. Sound travels through the water pipe this time.
Extras - Transmitting Mediums cont.
Sensitive ears
Materials: A rubber tube, a friend
Do This:
Mark the tube at the half-length point. Put the ends into your ears. Have the friend scratch the tube with a fingernail or a comb, and you can tell which side of the middle is scratched.
Comment:
The scratch sound flows both directions from the point scratched, but the ears are very sensitive, and can tell which side is scratched, even though the point is near the center of the tube Of course, the tube should be hanging behind the back when the scratching is done, so vision is not involved.
Sound Travels Through Solids
A. Insert heavy thread into the eye of a needle and tie it in a loop. Hold the needle in the groove of a revolving phonograph record, stretch the loop over a forefinger, and hold the finger in your ear. Remember, the thread must be stretched. You will hear the music distinctly.
B. Grip a penholder in your teeth and hold the pen point in the groove of a revolving record. Close both ears with your fingers and you will hear the music very distinctly.
Sound Travels Through Gases
Materials: A round balloon, an alarm clock or watch,
Do this:
Blow up the balloon, and hold it between the clock and the ear. Notice how distinct the ticking Is. Remove the balloon and see If the ticking is less loud.
Comment:
Carbon dioxide from the breath is heavier than air, and the balloon containing It is supposed to act as a converging lens to the sound waves, focusing them to the ear. The small amount of carbon dioxide in the balloon does not make any appreciable difference in the sound intensity.
To get more carbon dioxide into the balloon, mix baking soda and vinegar in a bottle and let the gas go into the balloon. The gas may be concentrated enough to produce the converging lens effect.
FUNdamentals of Sound
I. Characteristics Of A Wave
A. Pulse: a single disturbance in a medium.
B. Frequency: the number of occurrences of some event per unit of time. (example; the number of times the meter stick goes up and down in one minute.)
C. Amplitude: the measurement of the distance the medium moves from the zero point to the maximum displacement.( example; the distance of the very end of the meter stick - from standing still to the farthest distance away from that zero position.)
D. Wavelength: the distance along a wave front — from any starting point to the next successive starting point. (example; looking at a slinky in motion. Begin with the very beginning of a pulse to the very beginning of the next pulse.)
E. Loudness: this occurs when more and more energy is applied to the vibrating medium.
II. Components Of Light and Sound waves
A. Energy is needed to form any Light or Sound wave.
B Light waves are made by continuous succession of oscillating magnetic and electric fields. These fields travel as a wave, an EM (Electromagnetic) wave.
C. Sound waves are made by the vibrations (moving back and forth) of the particles of an object.
D. A medium is NOT needed to transport the Light energy.
E. A medium is needed to transport the Sound energy.
F. Waves are formed when energy is transported from one place to another.
III. Three Types Of Waves
A. Torsional waves when the disturbance occurs as a twisting effect in a plane that is perpendicular to the direction on the wave motion (examples: twisters, hurricanes, tornados).
B. Longitudinal waves when the disturbance occurs in the same direction of the wave motion. (examples: sound, people standing in line, cars taking off from one red light and coming to a stop at another red light.)
C. Transversal waves when the disturbance occurs at right angles to the direction of the wave motion. (examples: water, light, radio, electromagnetic.)
What Is A Sound Wave? (Frequency, Pitch and Wavelength)
Materials: Slinky, Open Hallway, String
Introduction
In previous investigations you have seen that objects, which vibrate rather rapidly, produce sounds. As the surface of a moving or vibrating object collides with particles surrounding it, these particles themselves may begin to move. Although far too small to be seen with your eyes, these particles are usually the molecules of the gases in air! (Think about the last time you heard and even felt the sound of a loud drum. Many very small particles of air were bumping into you!)
For example, if a vibrating surface first moves toward you, the air molecules are given a shove toward you also, crowding them together. These molecules then move toward their neighbors, and so on. This crowded region is called compression. When the vibrating surface moves backward, away from you, it leaves a somewhat empty space where it has just been. Molecules nearby then move over a bit, to fill in this recently vacated space. Of course, as they move over, they too leave a space behind. This uncrowned space is called a rarefaction.
Imagine putting on a pair of very high-powered magnifying glasses, so that you could see the molecules of air in the small rectangular space shown in the diagram below.
If the room was quiet, with little or no noticeable sound present, and you took a snapshot of the air molecules in this little rectangular space and magnified it, it might look like this:
If a very brief sound, that is a single pulse consisting of one compression and one rarefaction, was made by the Speaker on the left side of the drawing,
What Is A Sound Wave? (Frequency, Pitch and Wavelength) cont.
And you took a snapshot of the air molecules in the little rectangular space between the Speaker and the Listener and then magnified the photograph, it might now look like this:
If you had taken the snapshot a short time later it might have looked like this:
Does this pulse appear to have moved toward or away from the Speaker during the time in between when these snapshots were being taken?
Once the pulse has moved by, a snapshot of the air molecules in the little box might look like this (again). See following page.
What Is A Sound Wave? (Frequency, Pitch and Wavelength) cont.
If the pulse is repeated regularly, a pattern may be created. We call this pattern of compressions and rarefactions pressure waves, or sound waves. This is what Sound waves might actually look like!
As long as the vibration continues, pressure waves will be generated and move through the air. When waves reach your ears they push on your eardrums, vibrating them, too. It is these vibrations, converted to electrical signals in your inner ear. That your brain interprets as sound.
Here is a wave that you can see without any magnification:
Activity 1: A Human Wave
A. Go out in the open hallway, as this activity requires a good deal of open space. You will all form a single file line, facing in the same direction.
B. Place your hands on, and grasp the shoulders of the person in front of you. Gradually, extend your arms outward until they are straight.
C. When your line has settled down, have someone at the back of the line give the next person in front a light shove, followed, a second or two later, by a backwards pull.
D. Repeat several times. Remember to keep your arms straight.
These are called compressional waves. Scientists call them longitudinal waves because the wave moved along the same line as the disturbance (the push) which caused the wave.
Questions
1. Estimate the distance that this human wave traveled as it moved from the back of the line towards the front.
2. How far did you move during this wave motion? DESCRIBE your motion.
What Is A Sound Wave? (Frequency, Pitch and Wavelength) cont.
Idea:
Waves in humans and Slinky’s model the behavior of sound waves. Sound waves are compressional or longitudinal waves. Compressions are where the matter is crowded together. Rarefactions are the uncrowded spaces in between. Although the wave may travel a large distance, the particles involved move forward and backward only a little.
Duration: 30 Min.
Process Skills: Observe, Describe, Compare
Student background: Students should be familiar with sound as vibration.
Advance preparation: None.
Management tips:
You may want to tell neighboring teachers about the human wave activity before trying it.
Activity 1: A Human Wave
1. Estimates will vary. (The length of the single file line.)
2. A short distance (less than one meter). Forward and backward.
Activity: A Slinky Wave
Waves can also be demonstrated with a Slinky.
With a partner, stretch the Slinky to a length of about 3 or 4 meters while keeping the Slinky on the floor. Have a third person tie a short (10 cm) piece of string to a single coil of the Slinky near its center. An additional piece of string should be tied about one meter from one end, and a third piece the same distance from the other end.
a. START a wave pulse by pushing rapidly on your end of the Slinky toward your partner, and then pulling rapidly back (not by whipping it).
b. OBSERVE the motion of the strings as the compression and rarefaction move down the Slinky.
c. Have your partner firmly hold the other end of the Slinky. OBSERVE the reflection.
d. REPEAT with a series of rapid pulses.
Some earthquake waves (P waves) travel like these slinky waves. They too are compressional or longitudinal waves because the wave moves along the same line as the disturbance (the push) which caused the wave
.
QUESTIONS
1. How far did the Slinky wave travel from you to your partner?
2. Did any part of the Slinky move very far? DESCRIBE the motion of the pieces string.
3. COMPARE sound waves and these human and Slinky waves. DESCRIBE any similarities you may have noticed.
1. Three to four meters (from one end to the other).
2. No. Only a little forward and backward.
3. In all these waves, particles push on each other, but do not move very far themselves. They are all compressional (longitudinal). That is, the compressions and rarefactions all travel away from their source along the same line as the disturbance which caused them, yet the particles involved move forward and back only a short distance as the wave passes by.
Points To Emphasize In The Summary Discussion:
Sound waves are compressional or longitudinal waves. They can move only through matter (they will not pass through a vacuum).
Only if a participant raises the question, should the fact that longitudinal waves are sometimes represented graphically as transverse wave forms for the purpose of showing their wavelength and amplitude, be mentioned at this time.
Use a series of marbles or string-suspended metal balls to show how energy can be transmitted through matter by compressional forces. A line of dominoes can also be knocked down from the center outward to demonstrate this idea (as well as the idea that sound generally travels outward from its source).
What Causes High And Low Pitched Sounds?
Materials: string, weight, ruler, 4 straws, scissors, masking tape
1. Suspend the weight using a 60 cm long string tied to a pencil and taped to the edge of a table. You have made a pendulum. Although a pendulum moves back and forth too slowly to produce audible sound, it can demonstrate the relationship between the length of an object and how fast it vibrates Pull the suspended weight to one side and let it swing back and forth. RECORD how many times it makes a complete back and forth swing in one minute. One complete back and forth motion is called a vibration, oscillation or cycle.
2. Shorten the pendulum to a length of 30 cm. Again, count and RECORD the number of back and forth swings (vibrations) in one minute.
3. Repeat the test at a length of 15cm. Again, RECORD your results.
4. Use the words "faster" and "slower" to complete the following statements:
The longer the pendulum, the ________________it swings back and forth.
The shorter the pendulum, the ________________ it swings back and forth.
5. With one hand, hold a side of the ruler on the table. Now bend the other side of the ruler and let go. The ruler is moving back and forth (vibrating), but much more quickly than the pendulum. It is vibrating fast enough to produce a sound.
6. Move the ruler back and forth on the table so that different lengths extend from the table. Bend the ruler to produce vibrations at the different lengths. DESCRIBE the relationship between length and speed of vibration
7. Pitch is the highness or lowness of a sound. Pitch depends on how fast something vibrates. Fast vibrations produce a high pitch. Which length of the ruler produced the highest pitch and the lowest pitch?
8. Complete the following statements by using the words “high,” “low,” "fast" and “slow.” Long objects vibrate
______________________ and produce a ______________________ pitch.
Short objects vibrate ______________________ and produce a ______________________ pitch.
What Causes High And Low Pitched Sounds? Cont.
9. Make a straw whistle using the following procedure:
A. Flatten the end of a plastic drinking straw.
B. Cut the two sides of the flattened end to make a pointed end.
C. Practice making a sound with the straw by putting the pointed end in your mouth so that your lips are pressing the straw on the top and bottom at a point a little beyond the cut end (jaw end).
Blow air through the straw as you are pressing the ends with your lips. Sound is produced when the ends (jaws) of the straw vibrate.
10. Using what you have learned about pitch from the vibrating ruler, form a hypothesis about how the length of a straw will affect its pitch.
11. Test your hypothesis by making several straw whistles of varying lengths. Normal straws can be taped together with masking tape to make super long straws (some straws may be able to slip inside others). Also, cut with scissors to make shorter straws.
What did you discover?
What Causes High And Low Pitched Sounds? Cont.
Idea:
Sounds vary in pitch. Some are high and some are low. High-pitched sounds are caused by fast vibrations and low-pitched sounds are caused by slow vibrations.
Process Skills:
Observe
Compare
Describe
Test
Explain
Hypothesize
Duration: 45 min.
Student Background:
Students should know that vibrating matter produces disturbances in the air. These disturbances are transmitted by
Molecules in the air being compressed and rarefied. The disturbances are heard as a particular sound when they
Reach a receiver such as the ear. In this activity, students will use varying lengths of string for swinging pendulums, varying lengths of a vibrating ruler, and varying lengths of soda straw whistles as analogies of high and low pitched sounds. The students will discover that longer objects vibrate slower than short objects and are analogous to low pitched sounds. Shorter objects vibrate faster and are analogous to high pitched sounds.
Advance Preparation:
Materials should be assembled in trays or other containers for use by groups consisting of 2 to 3 students each. A large lead weight (1 to 3 ounces) from a fishing supply store works well as a pendulum bob, although any object of similar weight that is small, to reduce air resistance, will work.
Drinking straws can possibly be obtained as a donation from a local fast food establishment or cafeteria. Plastic straws are more durable, but paper straws also work well until the end gets bent or soggy.
Management Tips:
The ruler should be held firmly against the table top to prevent vibration between the ruler and the table top. We are interested in the sound produced as the end of the ruler extending from the table vibrates.
Students will discover that long objects vibrate slower and produce a lower pitch and short objects vibrate faster and produce a higher pitch.
The pendulum bob, although it does not make a sound, vibrates back and forth slowly enough for the students to dearly see the difference in length of the pendulum and speed of vibration. One back and forth swing is a complete vibration. Students will need some practice to learn to make a sound with the straw whistle. Sliding the end of the whistle back and forth between their lips will help locate the right spot to produce a sound.
What Causes High And Low Pitched Sounds? Cont.
Responses To Some Questions:
1. Approximately37times.
2. Approximately 54 times.
3. Approximately 78 times.
4. Slower, faster
6. The shorter the ruler, the faster it vibrates. The longer the ruler, the slower it vibrates.
7. The shortest length produced the highest pitch. The longest length produced the lowest pitch.
8. Slowly, low quickly, high
10. Answers will vary. The shorter the straw, the higher the pitch of the sound it produces.
11. The pitch of the Sound produced by vibrating straws increases as the length of the straw decreases.
Points To Emphasize In The Summary Discussion;
The main point is that the pitch of a Sound is dependent upon the length of the vibrating object. Loudness and pitch are two separate characteristics of sound. A straw whistle of a given length can be made to sound loud and soft, but the pitch is the same. The only way to change the pitch is to change the length.
Possible Extensions:
Play a 45 rpm record at 3 different speeds on a record player. At which speed is the pitch the lowest? The highest? Discuss this in terms of speed of vibration.
Try tying different lengths of string to washers, and find the number of swings in ten seconds. Then plot length vs. Number of swings. By using the blackboard, put the number of swings on the x-axis (horizontal line), and tape the strings themselves to the board at the proper places. A very nice inverse curve, results. Investigate the factors affecting the period of a pendulum.
Measure the rate of vibration (frequency) of the air coming from the straw whistle.
Resource: Although dated, an EXCELLENT set of TWO Cassettes. Science of Sound, from The Smithsonian Institution. 416 Hungerlord Drive, Suite 320. Rockville MD 20850. Folkways Cassette Series: 06007 (by Bell Labs.) Topics - Pitch and Frequency. Cost: $19.96. Contact person: Dudley Connell: Telephone (301) 443-2314. Inquire about a possible Operation Physics discount.
How Does The Pitch Change As A Moving Sound Source? (Doppler Effect)
Materials: a small nerf football, available in most discount stores a battery-operated piezoelectric buzzer, available from Radio Shack, and other electronic parts distributors a sharp blade tape
1. Obtain a “nerf football, buzzer, and battery from the teacher. Turn on the buzzer and insert it and the battery into the "nerf" football. Tape the gap shut. You have just constructed a movable sound source.
2. Try tossing it around a bit, listening to the sound, as the football is moving. DESCRIBE the sound produced.
3. Let someone else throw the football. Position yourself several meters away and note any difference in the pitch of the sound when the buzzer moves away from you as compared to when it is moving toward you.
DESCRIBE the difference.
4. Have you ever noticed the change in pitch that occurs as a moving train whistles or fire engine siren passes you? The higher pitch produced by an approaching sound-maker is a result of sound vibrations crowding together in front of the sound-maker. Vibrations reach your ear closer together and you hear a higher pitch. The lower pitch produced by a sound-maker a result of sound vibrations spreading out behind the sound maker. Vibrations reach your ear farther apart and you hear a lower pitch.
How Does The Pitch Change As A Moving Sound Source (Doppler Effect)? Cont.
5. Let's use circles to represent vibrations from a whistle. The circles get bigger and bigger as the vibrations move out from the whistle How many vibrations are shown for this whistle?
6. Suppose the whistle is not moving. Observers on all sides of the whistle hear the same pitch because the same number of vibrations reach each observer in a given period of time.
7. Now let’s suppose that the whistle is moving. The diagram shows waves crowding together in front of the moving whistle and spreading out behind the whistle.
A. In which direction is the whistle moving?
B. Which observer will hear the higher pitch?
8. Draw sound vibrations around the moving buzzer that is moving in the direction of the arrow. Write “HIGH” on the side of the whistle where an observer would hear a high-pitched sound and “LOW” on the side where an observer would hear a low- pitched sound.
How Does The Pitch Change As A Moving Sound Source (Doppler Effect)? Cont.
Idea:
If a vibrating object is moving. Sound waves crowd together in front to produce a high pitch and spread
apart behind to produce a low pitch.
Process Skills:
Observe
Describe
Duration: 30 Min.
Student Background:
Students should have the ability to discriminate between sounds of different pitches. Some practice in “hearing different pitches would be helpful prior to doing this activity. A small keyboard, or other sound-maker could be used for auditory discrimination between different pitches. Some may have trouble distinguishing between different pitched sounds. Many people are able to recall the change in sound that occurs at the precise moment a fire engine passes on the road.
Advance Preparation:
Sufficient materials should be gathered ahead of time so that preferably each student is able to construct a sound source. You should make an incision with a sharp blade in the "nerf" football large enough for the students to insert the buzzer and battery. For safety reasons, the students should not have access to the sharp blade. If it is not feasible to construct individual sound sources, one "Doppler Football” may be used as a demonstrator for each group, or even for the whole class.
Management Tips:
The buzzer appears to produces a higher pitched sound as it moves toward an observer and a lower pitched sound as it moves away from an observer. The phenomenon of a moving sound-maker being heard as a high pitch to an observer in front of it and a low pitch to an observer behind it is called the
Doppler Effect.
The students should note the higher and tower pitched Sounds as the football flies around. Some may perceive the sounds as loud and soft if they are not skilled at distinguishing between sounds of different pitches.
Responses To Some Questions:
2. The buzzer sounds higher pitched sometimes and lower-pitched at other times.
3. The sound has a higher pitch as it approaches an observer and a tower pitch as it moves away from an observer.
5. Five.
7. A. Toward Observer A. To the left.
B. Observer A will hear the higher pitch.
Pitch because the vibrations that reach his
ears are closer together.
How Does The Pitch Change As A Moving Sound Source (Doppler Effect)? Cont.
Points To Emphasize In The Summary Discussion:
High pitched sounds are produced by matter that vibrates quickly and lower pitched sounds are produced by matter that vibrates more slowly. The buzzer vibrates at a constant rate. It only seems to vibrate faster to an observer in front of it because the vibrations that reach the observer are closer together. For example, if someone on a moving bicycle was throwing balls to you at the rate of one every second, the balls would reach you faster than one per second as the bicycle approached you and slower than one per second as the bicycle moved away from you. This is because each succeeding ball has a shorter distance to travel as the bicycle moves toward you and each successive ball has a greater distance to travel as the bicycle moves away from you.
Doppler Affect
When a sound is moving with respect to the observer the sound's pitch appears to change. Because of the motion of the source, illustrated here as a racing car, the sound waves appear to be bunched up in front and spread out in back. This results in shorter wavelengths, or an increased frequency, in the front of the source and longer wavelengths, or a lower frequency behind the source.
Possible Extensions:
Use a tape recorder to record the sound of a whistle as someone on a bicycle blowing the whistle approaches and
Passes the recorder. Can the Doppler Effect be heard?
Another method of detecting the Doppler Effect can be done using a cylindrical whistle and rubber tubing. The whistle is inserted into a 1 meter (1 yard +) length of rubber tubing of a size that will allow a tight fit. Someone blows the whistle from the end of the rubber tubing while turning around and around swinging the tubing. Observers should note the alternating high and low sounds.
Resource: Although dated, an EXCELLENT set of TWO Cassettes, “Science of Sound”, from The Smithsonian Institution, 416 Hungerford Drive, Suite 320, rockviue, MD 20850. Folkways Cassette Series: 06007 (by Bell Labs.) Topic - The Doppler Effect . Cost: $19.96. Contact person: Dudley Connell Telephone (301) 443-2314. Inquire about a possible Operation Physics discount.
Loudness, Energy and Amplitude Using The Slinky
Waves can be demonstrated with a Slinky. With a partner, stretch the Slinky to a length of about 3 or 4 meters while keeping the Slinky on the floor. Have a third person tie a short (10 cm) piece of string to a single coil of the Slinky near its center. An additional piece of string should be tied about one meter from one end, and a third piece the same distance from the other end.
A. START a wave pulse by pushing rapidly on your end of the Slinky toward your partner, and then pulling rapidly back (not by whipping it).
B. OBSERVE the motion of the strings as the compression and rarefaction move down the Slinky.
C. Add more energy – make the pulse larger. Observe the affect on the wave pattern as it moves down the Slinky
D. REPEAT using various amounts of energy.
QUESTIONS
1. How far did the Slinky wave travel from you to your partner?
2. Did any part of the Slinky move very far? DESCRIBE the motion of the pieces string.
3. COMPARE sound waves from your voice human and Slinky waves.
DESCRIBE any similarities you may have noticed.
Check your Understanding the Model of Sound
1. The following drawings indicate a model of a sound. The frequency of each sound is the number of vibrations occurring each second or f = vibrations/sec. For each sound count the number of waves, determine the time for those waves and calculate the frequency of each sound.
| |Sound Model |
| |
|4. Which sounds have the same frequency but different loudness? C and E |
|5. Which sound is the highest frequency? I 6. Which sound is the lowest frequency? B |
Extras - The Model
Compression and Rarefaction Waves in Air
In a large room with two doors, close all the windows and other large openings.
Open one door one or two inches, and then open the other door rapidly. The compression produced will close the first door almost instantly, with a bang.
Open one door about 4” and then close the other rapidly. The rarefaction produced will swing the first door open quickly.
Water Waves and Sound Waves
A. Run a little water into a bathtub, let the surface become still, and then dip a finger in and out. You will see a series of waves spread out rapidly in perfect circles.
B. Dip two fingers in and out, about one foot apart. You will see two series of waves go through each other. Each will spread out in perfect circles as though the other were not there.
Similarly, sound waves spread out in air, but as perfect spheres, and thousands of sound waves can move through one another in the same air at the same time. Each will spread Out as a perfect sphere, as though the others were not there.
The singing wire.
Materials
Copper wire. A strong magnet, a toy transformer and supports. (A spring is good but not necessary.)
Procedure
Stretch a few feet of the wire between Supports (nails will do) and hold it with a spring or tighten It by hand around a nail. Connect the wire to the transformer, and move the magnet along the wire until the wire vibrates. The position of the magnet and tension on the wire will control the vibration.
What Happens:
The wire carries an alternating current, producing magnetic lines of force that Interact with the lines from the permanent magnet, producing alternately attraction and repulsion of the wire. The wire vibrates In accordance with the rules regarding vibration of a string, showing one or more nodes. The vibration may produce an audible musical sound.
Compression and Rarefaction Waves in Air
On a day when there is no wind, raise the lower sash of a window to its full height and pull down the shade. Close all the doors and all the other windows. Now open a door rapidly, and the compression it produces will swing the shade out almost instantly. Open the door wide, then close it rapidly. The rare-faction it produces will swing the shade in quickly.
Extras –The Model cont.
The Roaring Ruler
Materials: A ruler, A piece of broomstick, Stout string, Drill for making holes in wood
Make a hole in one end of the ruler and the broomstick. You don't have to have a broomstick. Any strong stick of wood will work. Tie the ruler to the broomstick with a long loop of stout string. Now swing the broomstick in a circle, making the ruler swing around in a larger circle.
The ruler roars because when you, swing it through the air the ruler spins very fast in such a way that it winds up the loop of string. It does this so hard and so fast that it sends out vibrations through the air which you hear as a roaring sound. This roaring stops when the string is all wound up as tight as it will go. Then the ruler spins the other way and roars as it unwinds the string. The whole process starts all over.
A Major Chord in Air Columns
The vibration frequencies of the notes in any major chord are in the ratio 4:5:6:8.
4 4 4 4
The air columns which produce these notes have volumes in the Ratios — ; — ; —; and —.
4 5 6 8
To illustrate this, take four 12-ounce bottles of the same shape. The air volume in an empty bottle is the volume of 12 ounces of water. Call the note of this air volume do. Then:
Do is produced by air volume . . . . . . . . . . . . . . . 12
Mi is produced by air volume . . . . . . . 12 x 4/5 = 9.6
Sol is produced by air volume . . . . . . . 12 x 4/6 = 8
Do is produced by air volume . . . . . . . 12 x 4/8 = 6
The bottles weigh 26 ounces when full of water and 14 ounces when empty. Hence the weights of the bottles, plus water to give the air volumes for a major chord, are the following:
For do, 26-12= 14 ounces.
For mi, 26-9.6 = 16.4 ounces.
For sol, 26-8 = 18 ounces.
For do, 26-6=20 ounces.
Prepare the bottles as shown. Then sound the air columns in order, beginning with the longest or the shortest, and you will hear a major chord.
Get The Point – Make Sound With Pins
Materials: Common straight pins, a board (or, better yet, a wooden cigar box), A piece of dowel or a pencil, Hammer, Pliers
Into the light board or the wooden cigar box, drive the pins in a straight line. You’ll probably have to cut off Some of the pins with the pliers, else you’ll bend them when you try to drive them into the wood. Notice how short the pins get toward the right side of the line.
Mount another pin in a dowel or the eraser end of a pencil and use it to pluck the pins in the board. The notes you hear will depend on how much of each pin is free to vibrate. The longer pins are your low notes and the shorter pins your higher notes. Tune each pin to the scale by pounding it further into the wood if it’s too low and pulling it out slightly with the pliers if it’s too high. The wooden cigar box will produce better music because it’s a better sounding box than a plain board. You aren’t very likely to find an instrument in a symphony orchestra that works on the principle of vibrating pins, but you’ve heard the music of instruments that do many times.
Extras – The Model cont.
The Sound Box
Materials: A box (of cardboard, metal or wood), Pencil, String, Resin, Knife
Tie the string around the center of the pencil.
With the knife, cut a hole in one side of the box and put the string through it with the pencil inside the box. Rub plenty of resin on the string. Hold the box with one hand and pull the string with the other.
You will hear a lion’s roar, a dog’s bark or a jungle bird’s cry depending upon the size of the box and how you pull the string. What makes these strange sounds come from a box? Let’s find out.
When you pull on the string coated with resin you’ll find that your hand sticks slightly. This makes your hand move in a series of short, fast jerks. This quick jerking motion sets the pencil to vibrating and it vibrates the whole box. A small box will vibrate fast, sending out a high-pitched sound like a jungle bird. A larger box will vibrate more slowly—a lion’s roar. A medium-sized box, and a series of jerks with the hand on the string—a dog barking. Try all kinds of sizes of boxes and you’ll get all kinds of eerie sounds.
You can see why a small box sends out a high-pitched sound and a larger box a lower-pitched sound when you watch the ruler you vibrated on the table.
A set of dinner chimes
Secure a straight steel pipe about 3 cm in diameter and about 3.5 m in length. Cut it into four parts, 100 cm, 90 cm, 80 cm and 70 cm. Drill holes through both sides of each pipe near one end, and suspend them. Let them hang freely. Strike each pipe in turn with a rubber hammer and compose a sort of signature chime for your class.
Pop Bottle Trombone
Materials: Pop bottle, Glass tube, Water
Hold the bottle in one hand and the end of the glass tube in the other. Adjust the angle of the opening at the end of the tube until you can blow a note across it. As you blow, move the bottle up and down. You’ll hear various notes as you change the length of the column of air vibrating in the tube. You’ve probably figured out that it’s the trombone which works like that.
When you played your pop-bottle “trombone’ you made music all right, but how? No reeds! Blow another note on your “trombone.” Then take out the glass tube, dump the water out of the bottle and blow across its mouth like you did the glass tube.
A pleasant note comes out of the bottle. It’s a lot lower than any of those you could play on the “trombone.” Doesn’t that suggest what’s vibrating? The air in the bottle (and in that part of the glass tube above the water in your pop-bottle “trombone") is vibrating, all right.
Extras – The Model cont.
Rip and tear.
Materials: A piece of cloth.
Procedure:
Rip or tear the cloth The faster it is torn, the higher the pitch of the Sound made.
Outcomes:
Each time a thread breaks It sets up a vibration of the air around it. If the threads are broken at a faster rate, the vibrations come faster and the pitch of the Sound is higher.
Bottle noise.
Materials: A bottle and a faucet.
Procedure:
Run water into the bottle; the pitch of the bubbly noise gets higher. Pour water out, and the pitch of the noise gets lower.
Outcomes:
Many Frequencies of sound are made by the bubbling water, but those that excite the air column in the bottle are heard more clearly as the air column resonates. The resonant frequencies are determined by the volume of air In the column, or length of the air column, and as the air volume increases the frequency increases.
The Loud Fork
Materials: Table fork
Empty coffee can
Rap the fork and touch the handle of it to the edge of the coffee can. You’ll hear a loud pleasant sound. Does the coffee can have to be empty? Yes. Why? Because for it to work as a sounding box and increase the volume of the sound it must be able to vibrate as fast as the fork. The sounding box, whatever it is made of, can’t be too heavy or it will be hard to set it moving back and forth. The coffee in the can will prevent the can from vibrating very much. The idea is to get the air around the can moving with as much force as possible. The easier it is
Two Ways That One Vibrating Object Can Cause Another To Vibrate?
Materials: ball of String, 2 large fishing sinkers of different sizes, plastic straw, 3 large metal washers of the same size, tuning fork
1. Tie a string between two supports, such as desks or chairs. Stretch the string tightly.
2. Cut two equal lengths of string and suspend each sinker from the stretched strings to produce two independent pendulums as shown.
3. Start one pendulum swinging. While the one pendulum is swinging, OBSERVE what happens to the second pendulum and RECORD your observations.
4. Change the length of one pendulum so that it is not the same as the other. Start one pendulum swinging and OBSERVE the other. DESCRIBE any difference between the behavior of the second pendulum now compared to when the second pendulum was the same length as the first pendulum.
5. All objects have a natural vibrating frequency that depends on such factors as the elasticity and shape of the object. An object can be forced to vibrate at a frequency different than its natural frequency, but it vibrates most readily at its natural frequency. The two pendulums that are the same length have the same natural frequency. When one swings at its natural frequency, the vibrations produced in the air and the tight string set the other pendulum to swinging at the same natural frequency. This is known as resonance or sympathetic vibrations. When the pendulums have different lengths, resonance does not occur because the two pendulums do not have the same frequency.
6. Suspend the 3 washers from the straw by strings of different lengths. Twist the straw back and forth to make each pendulum swing. Can you keep all the pendulums swinging at the same time? EXPLAIN.
7. As mentioned earlier, an object can be forced to vibrate faster or slower than its natural frequency This is called forced vibration. Strike a tuning fork and then place the stem against a table top. DESCRIBE what change takes place in the sound as the stem is pressed against the table top.
8. Forced vibrations set more air molecules in motion, thus a more intense (louder) Sound results. The sounding boards of stringed instruments use forced vibrations to amplify the sound produced by the vibrating strings.
Two Ways That One Vibrating Object Can Cause Another To Vibrate? Cont.
A vibrating object in contact with a second object can force the second object to vibrate or it can induce a second object with the same natural frequency to vibrate even though the two objects are not in contact.
Process Skills:
Observe, Record, Describe, Explain, Compare
Duration: 45 Min.
Background:
Students should know that the frequency of a vibrating object is the number of back and forth movements it makes in a given period of time. The number of back and forth swings of a child on a swing in a minute is one experience students can transfer to the principle of frequency. If two vibrating objects are made of the same material and are the same length, their frequency will be the same. All objects have a natural frequency at which they vibrate on their own when disturbed. They can be forced to vibrate slower or faster but are inclined to vibrate at their natural frequency.
Advance Preparation:
The fishing sinkers do not need to be the same size. For the pendulums, frequency depends on length, not weight. In fact, sympathetic vibrations or resonance will occur more readily if the large sinker pendulum is used to resonate with the small sinker pendulum. The washers should all be the same size so that students do not attribute the inability to get all three to swing at the same time to differences in washer size. The effect is the same whether the washers are different sizes or all the same size.
Management Tips:
When a vibrating object is forced against another object the second is forced to vibrate. (A parallel that might be useful) When you grab someone by the shoulders and vibrate your hands back and forth, the persons shoulders are forced to move back and forth at the same frequency as yours). The combination of the original vibrating object and the forced vibrations of the second produce a bigger (not faster) vibration in the surrounding air. This results in a louder sound. Sympathetic vibrations (or resonance) result when two objects have the same natural frequency. One object vibrates and produces air disturbances just far enough apart to stimulate the second object to begin vibrating.
Responses To Some Questions:
3. The second pendulum starts to swing with little movement at first and then greater movement after awhile.
4. The second pendulum shakes erratically but never really swings like the second pendulum did in #3.
6. No. The natural frequencies of the three pendulums are all different. The frequency of the twisting motion may produce resonance in one of the pendulums, but not all three at the same time.
7. As the tuning fork stem presses against the tabletop, the sound from the fork becomes louder.
Points To Emphasize In The Summary Discussion:
The main point to emphasize is that a vibrating object has an effect both on objects it is in contact with and on other objects with the same natural frequency with which it is not in contact. Forced vibrations and resonance are common happenings that amplify (increase loudness of) sounds. Megaphones, sounding boards of violins, and even the bones and sinuses of the human head help amplify sounds through both forced vibrations and resonance.
Possible Extensions:
Show the video "Tacoma Narrows Bridge Collapse.” An apparatus known as the resonance tuning forks would be a meaningful addition. Two identical tuning forks, one adjustable, are attached to wooden boxes (one each). When one is struck, the will begin vibrating also If they are tuned to a frequency near enough to one another.
Resource: Although dated, an excellent set of two Cassettes, Science of Sound”, from The Smithsonian Institution, 416 Hungerford Drive, Suite 320, Rockville MD 20850. Folkways Cassette Series: 06007 (by Bell Labs.) Topic Vibration and Resonance. Cost: $19.96. Telephone (301) 443-2314.
Resonating Bar
Background: Most objects have one or more natural vibrating frequencies. Tap the rim of a stemmed goblet, for example, and it will vibrate, producing a pleasant tone that is probably composed of a combination of frequencies referred to as harmonics. The lowest frequency is called the fundamental, while the higher frequencies---which are whole number multiples of the fundamentals - - are overtones. The pitch of the tone produced by the glass is determined by the fundamental.
Materials:
1. An aluminum solid bar or hollow pipe (3/4” or 2 an diameter and about 3’ or 1 m long).
2. A damp cloth.
Procedure:
1. Let the aluminum bar balance on your right hand, by holding it between forefinger and thumb in the middle of the bar.
2. Rub the left hand side of the bar with the damp cloth or rosin, slowly and gripping the bar rather lightly (try this several times until a high pitched tone is produced).
3. If the rubbing does not succeed, tap the bar vertically on a hard surface or hit the end of the bar with a hard object.
4. Stop the vibration by holding the bar on either end of the center with the left hand.
5. This time hold the rod at 1/4 of the length from one end. Again slide the thumb and forefinger along the greater length toward the end. Notice that the pitch of the sound is much higher. This means that the wavelength must be shorter.
Questions:
1. What did the rubbing of the bar do to it?
2. Why does the rubbing as well as the tapping produce the same tone in the bar?
3. Would hitting the bar on the side produce the same tone?
4. Why can the vibration be stopped on the side of the bar that was not rubbed or hit?
Explanation:
The rubbing the aluminum bar made the cloth or fingers slip and grab, slip and grab alternately, causing the bar to vibrate. You have produced a standing wave in the rod with a node in the center and an antinode at each end. This is obvious from the fact that the rod keeps vibrating for a while as long as you touch it only in the center. But if you touch it at an end, the sound stops immediately. Please understand that the diagrams are only intended to show the locations of nodes and antinodes, not the actual appearance of the vibrations.
IV. Applying The Model
Using Resonance to Determine the Speed of Sound
Objectives
1. Given the following list of terms, identify each term's correct definition. Conversely, given the definition, identify the correct term.
amplitude, frequency, interference, loudness, intensity, period, resonance, sound, vibration, wavelength
2. Given various Celsius temperatures (T), calculate the speed of sound, using the relationship:
VT = 330 m/sec. + (.6 m/sec. 0C x T).
3. Given any two of the three variables, and the formula V = f x l, calculate the third variable, whether speed of sound, frequency, or wavelength.
4. Measure the length of a resonating column, and calculate the wavelength of the sound wave, using the following formula: wavelength = 4 x length.
Resonance
[pic]
Figure 5 Resonance in a Closed Tube
You may have noticed that a person singing, or a sound from the radio or television can cause some object in the room to vibrate. This is referred to as resonance. (Is it live, or is it Memorex?) Resonance occurs when the natural rates of vibration of two objects are the same. If you hold a vibrating tuning fork over a plastic cylinder as shown in the Figure, you can observe resonance. You will need to adjust the length of the tube by moving it up and down, until the sound produced seems the loudest. The following paragraph and Figure will explain how the sound becomes louder.
When a vibrating tuning fork is in the 'down' position (b), the sound wave travels down the tube, reflects off the water, and returns to the tuning fork, just as it reaches the 'up' position (a). The reflected sound reinforces the sound made by the tuning fork, making it seem louder. The sound has gone down the length of the tube (L) and back; or 2L, in half of a wavelength, (distance "a" to "b"). The length of the tube is half a wavelength divided by 2, or 1/4 wavelength. The length of the tube is one-quarter of the wavelength of the sound being produced. To determine the wavelength of the sound produced multiply the length of the tube by four. This relationship can be expressed as: l = 4 x L
By investigating the relationship between frequency (vib/sec) and wavelength (m/vib) one would observe that if they are multiplied together and we cancel appropriate units the results would be units of (m/sec).
[pic]
The units of (m/sec) represents velocity. Therefore the determination of velocity can be expressed as:
V = f x l
Since the tuning forks are stamped with their frequency (f) and the wavelength (l) can be obtained through resonance we can calculate the velocity of sound in the classroom.
`
Procedure to Use Resonance to Determine the Speed of Sound
1. Clamp the smaller (2.54 cm.) diameter plastic tube in a vertical position on a ring stand.
2. Place a container filled with water to within approximately 2-3-cm. of the top under the tube.
3. Start the tuning fork vibrating by striking it on the rubber mat provided.
4. Hold the vibrating tuning fork over the tube, and adjust the position of the tube in the water by raising it or lowering it until the sound from the vibrating tuning fork is intensified. This is the point at which resonance occurs. Clamp the tube so an accurate measurement can be made.
5. Measure the length of the air column in the tube (in meters) from the surface of the water to the top of the tube, (L). The wavelength (l) of the sound is equal to four times the length of the air column.
Remember: When a vibrating tuning fork is in 'down' position, the sound wave travels down the tube, reflect off the water, and returns to the tuning fork, just as it reaches the 'up' position. The reflected sound reinforces the sound made by the tuning fork, making it seem louder. The sound has gone down the length of the tube and back; or 2L, in half of a wavelength. The length of the tube is therefore one-forth the wavelength. To determine the wavelength of the sound produced multiply the length of the tube by four. This relationship can be expressed as:
l = 4 x L (Record this value in meters.)
6. The number stamped on the tuning fork (480, 512), is the frequency (f) of the sound.
7. The velocity of sound is equal to the product of the wavelength and frequency. VE = f x l. This velocity of sound will be considered the experimental value.
8. Compute the velocity of sound in air at room temperature.
a. Measure the room temperature using the thermometer
b. Compute the velocity of sound using:
VT = 330 m/sec. + (.6 m/sec.0C x T)
c. This velocity of sound will be considered the theoretical value.
9. Compute error/percentage of error using the above values of VE and VT, and record them. If your value for the percentage of error is more than 10%, look closely for errors, and repeat the experiment.
10. Repeat steps 1- 9, using a tuning fork with a different frequency, (512).
11. Repeat Steps 1-10 of the procedure, using the larger (5.08 cm.) diameter plastic tube.
Data Table
|2 cm. Resonance Tube |480 Hertz Tuning Fork |512 Hertz Tuning Fork |
|(5) Length of air column in tube. L | |meters | |meters |
|(5) Wavelength l = 4 x L | |meters | |meters |
|(7) Velocity of sound Exp. VE = f x l | |meter/sec | |meter/sec |
|(8) Velocity of sound (air temp.) Theo. | |meter/sec | |meter/sec |
|VT = 330 m/sec.+ (.6 m/sec. 0C x T) | | | | |
|(9) Error = VE – V T | |meter /sec | |Meter/sec |
|(9) % Error = 100 x Error / V T | |% | |% |
|1. Compare the pitch of each tuning fork. |
|2. Compare the loudness of each tuning fork. |
|5 cm. Resonance Tube |480 Hertz Tuning Fork |512 Hertz Tuning Fork |
|(5) Length of air column in tube. L | |meters | |meters |
|(5) Wavelength l = 4 x L | |meters | |meters |
|(7) Velocity of sound Exp. VE = f x l | |meter/sec | |meter/sec |
|(8) Velocity of sound Theo. | |meter/sec | |meter/sec |
|VT = 330 m/sec.+ (.6 m/sec. 0C x T) | | | | |
|(9) Error = VE – V T | |meter /sec | |Meter/sec |
|(9) % Error = 100 x Error / V T | |% | |% |
|1. Compare the pitch of each tuning fork. |
|2. Compare the loudness of each tuning fork. |
|3. What effect did changing the tuning forks (frequency) have on resonance? |
|4. What effect did changing the tube diameter have on resonance? |
Speed of Sound in a Parking Lot
By: Jan Paul Dabrowski
Consider this 1922 description of a demonstration of the speed of sound in air:
When a pistol is fired at a distance of several hundred feet, we see the flash a few seconds before we hear the report. The interval is the time required for the sound to travel the intervening distance, since for short distances light is practically instantaneous.1
In order to recreate this experiment for an introductory physics class-without gunplay-we substituted an inexpensive air horn2 for the pistol Other equipment included a standard camera strobe flash and a strobe sound trigger.3 This apparatus costs about $30.
The operation is straightforward. The flash is plugged into the sound trigger and positioned next to the air horn. When the horn is blasted, the sound trigger flashes the strobe. One group of students operated the air horn/strobe "pistol." Another group, with stopwatches, was located several hundred meters away. When the "pistol" was fired, these students started their watches at the instant they saw the strobe flash and stopped them when the sound from the air horn was heard. As a safety precaution, students in the group with the air horn should wear ear plugs.
Using the measured distance and the averaged stopwatch readings, the class calculated the speed of sound using a distance of 343 m and the mean time of 0.97s.
V = d/t
V = 343 m. / 0.97 s
V = 354 m/s
This compares well with the predicted speed for the air temperature at the time (13°C) of our experiment. This is calculated from the temperature-dependent equation where V. is the speed of sound at temperature T, and Vo is the speed of sound at O°C.4
V = Vo + (0.61 x T)
V = 331 + (0.61 x T)
V = 331 + (0.6 x 13°C)
V = 339 m/s
Assuming the temperature based calculation to be our theoretical we can calculate the percent of error for our experiment.
[pic]
% Error = [pic]
% Error = 4.4
This class then spent time discussing the procedure and analyzing the sources of error. The students felt the measured distance may have contributed an error. The assumption that the strobe flash reached the observers "instantaneously" was agreed to be acceptable since the light travel time over this distance was about a microsecond. Another error contribution could have been the reaction time, or more specifically, the difference in reaction time due to a visual vs. an audible stimulus.
References
1. C.E. Dull, Essentials of Modern Physics (Henry Holt, New York, 1922), p. 237.
2. Super Sound Air Horns, Falcon Safety Products, Inc., Mountainside, NJ 07092. These are used by boaters and can be found in most sporting goods stores. The horn is very loud and should be used with caution. It can easily be heard over a half mile away.
3. Sound Trigger Kit, Chaney Electronics, P.O. Box 4116, Scottsdale, AZ 85261, Stock Number C4740. Ph: 1-602-451-9407
4. F.J. Beuche, Introduction to Physics for Scientists and Engineers (McGraw-Hill, New York, 1985), p. 578.
Using Goldwave to Measure the frequency of a Sound?
1. Step 1 (a-f), provides the procedure for determining the frequency of a sound using the computer. For this example we will use a tuning fork with a known frequency of 512 Hertz. This is done just to practice the procedure. (You may want to try this on your computer)
a. Using the computer program GoldWave record the sound by:
1) Make sure GoldWave is on your computer. If it is not follow directions with disk provided. Run GoldWave and you should see:
[pic]
2) Click on 'File' and then click on NEW and you should see this window:
[pic]
3) Click on 'OK' and you should see this window:
Using Goldwave to Measure the frequency of a Sound? Cont.
4) Find the record button located in the Device Controls window.
[pic]
5) Produce a sound or strike the tuning fork on the mat provided. Hold the tuning fork near the microphone and click the record button.
6) After recording the sound the computer screen will look something like the following.
[pic]
b. To adjust the wave (sound) pattern so a traditional wave pattern can be seen and that has approximately ten waves are displayed on the screen select “View” and chose 1:1 view. The screen should look something like this:
Using Goldwave to Measure the frequency of a Sound? Cont.
If your wave pattern does not allow you to clearly see ten waves, whether the waves are to big or too small, chose the “View” and select “Zoom”. “Zoom” in or out until you can see ten or more waves.
c. Select a portion of your wave pattern, by moving the slide control, that most closely looks likes the picture. Move the mouse to the crest, (top), of a wave and click the right mouse button then move the mouse exactly ten waves and click the left mouse key. This will highlight the ten waves.
d. To find the time for one wave: (You must return to the 1:1 “View” to read your start and end times. Your ten wave marking will remain.)
1) The start or end time for our ten waves can be obtained by placing the cursor over the line marking the start or end of the ten waves. The time is indicated at the bottom of the screen (currently showing end time). Please note the time indicated is only the decimal portion of the time. The whole number portion of your time is obtained by looking at the top scale.
[pic]
i.e.: .00705 This is the start time for ten waves and is expressed in seconds.
2) The end time for our ten waves can be obtained by placing the cursor over the right end of the ten waves and record the time indicated at the bottom of the screen. In our example we found it to be: .02658 seconds. The total time for ten waves would be (end time - start time) or (.02658 sec. - .00705 sec.) which is .01953 seconds.
3) To find the time for one wave divide by ten.
.01957 sec. for ten waves / 10 = .001957 sec. per one wave
e. To find the number of waves in one second divide one second by the amount of time needed for one wave. Note: this result would be the experimental value.
waves per second = 1 sec / .001957 seconds
510.9 waves per second or 510.9 hertz.
Using Goldwave to Measure the frequency of a Sound? Cont.
f. Read the number on the tuning fork using this number as the theoretical value and calculate your percentage of error. For our example, the frequency is 512.0 hertz.
%Error = ((experimental value - theoretical value) x 100) / theoretical
%Error = ((510.9 hertz - 512.0 hertz) x 100 ) / 512.0 hertz
%Error = .21
2. Use the procedure, indicated in step 1 determine the frequency of a tuning fork with a known frequency of 480 hertz. Record your data and calculate the percent of error.
Determine the frequency of an Unknown source of sound.
Please note: The pan flute is the device that will be used to produce two sounds. The frequency of each of these sounds will then be determined. Since you need to blow on it we suggest that you wash it with soap and hot water. This procedure should ensure the safest and cleanest approach to using this device.
1. Determine the frequency of a known source of sound using the computer and the procedure you have just practiced. Record the designation written on the sound source.
2. Check your experimental frequency with the known frequency.
3. Calculate the percent of error.
4. Determine the frequency of an Unknown of sound.
a. Determine the frequency of a unknown source of sound using the computer and the procedure you have just practiced. Record the designation written on the sound source.
c. Check your experimental frequency with your instructor. If the results are close enough to the correct frequency, the instructor will provide the theoretical frequency.
d. Calculate the percent of error.
|1. Determining the frequency of a Known source of sound (480) |
|a. End time for 10 waves: | |seconds |
|b. Start time for 10 waves: | |seconds |
|c. Time for ten waves: | |seconds |
|d. Time for one wave: | |seconds |
|e. Experimental Frequency: | |Hertz |
|f. Percentage of Error: | |% |
|2. Determining the frequency of an Unknown source of sound. |
| Label On the Sound Source |
|a. End time for 10 waves: | |seconds |
|b. Start time for 10 waves: | |seconds |
|c. Time for ten waves: | |seconds |
|d. Time for one wave: | |seconds |
|e. Experimental Frequency: | |Hertz |
|f. Theoretical Frequency: | |Hertz |
|g. Percentage of Error: | |% |
|3. Determining the frequency of an Unknown source of sound. |
| Label On the Sound Source |
|a. End time for 10 waves: | |seconds |
|b. Start time for 10 waves: | |seconds |
|c. Time for ten waves: | |seconds |
|d. Time for one wave: | |seconds |
|e. Experimental Frequency: | |Hertz |
|f. Theoretical Frequency: | |Hertz |
|g. Percentage of Error: | |% |
How Does A Record Produce Sound?
Materials: old 78 rpm phonograph record player, sheet of writing paper straight pin piece of cellophane tape scissors
1. Roll the paper into a cone and use tape to hold the cone together. You may use scissors to even the opening of the cone.
2. Stick the straight pin through the tip of the cone. Turn on the record player. Hold the cone so that the pin is in the record grooves on the turntable and hold your ear to the opening of the cone.
Can you hear a sound from the record? describe the sound.
3. Sounds are always produced by vibrating matter. What matter is vibrating to produce sound from the phonograph record?
4. Try this with the pin only (no cone). What do you notice? What is the purpose of the paper cone?
How Does A Record Produce Sound? Cont.
Idea: Sound can be recorded on records, magnetic tapes, and on laser disks.
Process Skills:
Observe
Describe
Explain
Duration: 30 Min.
Background:
Students are most likely familiar with records, cassette tapes, and compact disks (laser disks). This activity is designed to illustrate how a sound pickup device can transform the grooves on a record into sound.
Advance Preparation:
Old 78 rpm records need to be located. 33rpm and 45rpm records do not work as well. A record player also needs to be available for this activity.
Management Tips:
The paper cone produces a louder sound if held at the large open end, rather than at the pointed end close to the pin.
Responses To Some Questions:
2. The music and/or words on the record can be heard.
3. The pin is vibrating. The vibrating pin sets up force vibrations in the paper cone that amplify the sound.
4. The paper cone vibrates with the pin to increase the volume of the sound.
Points To Emphasize In The Summary Discussion:
The sound of the singer/musician is converted into the mechanical energy needed to produce grooves in the record. When playing the record, the grooves vibrate the needle and it reproduces the original sounds. A phonograph groove is not straight, but is full of wavy bumps and dips. As the wavy, bumpy groove passes against the needle, it causes the needle to vibrate. The needle vibrations, in turn, force the paper cone to vibrate. These forced vibrations set the air to vibrating more than would the pin alone. This effect of forced vibrations on the cone is called amplification. The cone serves to amplify the sound. The grooves of a 45 rpm or a 33 rpm are too small and fragile, don’t produce much sound, and are easily damaged.
Other sound recordings use magnetic tapes that cause a certain electrical current to be produced when the tapes are played back. The current is then transformed back into sound in a speaker. Compact disks use laser technology to record sounds.
Possible Extensions:
Research different methods of recording sound and give a report.
Extras - Applications
The Wires Sing
Raise the lid of a piano, depress the loud pedal, and sing a single note loudly into the piano. You will hear the piano sing the same note. Sing another note into the piano and you will hear the piano sing it also,
Both Bottles Sing
Find two small empty bottles of the same size and shape. Hold the mouth of one just below your lips and the mouth of the other near, but not touching, your ear. Blow across the mouth of the first bottle to make it sing out a musical note. You will hear the second bottle singing the same note. You will get best results with small bottles.
The Resonating Tube.
Materials:
Two vacuum cleaner tubes or other tubes.
Procedure:
Clean the tubes. Hold one to your mouth and hum into it, varying the pitch. At one point a condition called the resonant frequency will be reached, and the tube will be felt to vibrate.
Outcomes:
The resonant frequency of a column of air in a tube depends on the speed of Sound in air and the length of the tube. A longer tube has a lower-pitched resonant frequency; when you hum into two tubes placed together end to end, you will have to hum at a lower pitch to make the tubes vibrate.
Another Sounding Board
A. Hold a needle in the groove of a revolving phonograph
record, and you will hear a slight sound.
B. Fasten the needle securely near one corner of a large piece
of cardboard and repeat. You will hear louder sounds.
C. Hold your ear against the cardboard. You will hear much
louder sounds.
Another simple reproducer
For a more effective homemade reproducer you can copy the early phonographs by using a horn. Substitute for the card or the matchbox a horn made out of a square sheet of heavy wrapping paper, about 40 x 40 cm.
Extras - Applications cont.
Resonant Rings
This device graphically demonstrates that objects of different size and stiffness tend to vibrate at different frequencies.
Assembly
Cut four or five 1-inch wide strips from the construction paper. The longest strip should be about 20-inch long, and each successive strip should be about 3’ shorter than the previous one. Form the strips into rings by taping the two ends of each strip together. Then tape the rings to the cardboard sheet as shown in the picture.
To Do and Notice
Shake the cardboard sheet back and forth. Start at very low frequencies and slowly increase the frequency of your shaking, Notice that different rings vibrate strongly, or resonate, at different frequencies. The largest ring will begin to vibrate strongly first followed by the second largest, and so on. The smallest ring starts to vibrate at the highest frequencies.
Keep shaking the cardboard faster and faster, and notice that the largest ring will begin to vibrate strongly again. Each ring will vibrate at more than one frequency, but the shape of each ring will be different for each resonant frequency. The rings will also have different resonant frequencies if you shake the board up and down instead of sideways.
Outcomes:
The frequencies at which each ring vibrates most easily (its resonant frequencies are determined by several factors, including the ring’s inertia (mass) and stiffness. Suffer objects have higher resonant frequencies, while more massive ones have lower resonant frequencies. The biggest ring has the largest mass and the least stiffness, so it has the lowest resonant frequency. Put another way, the largest ring takes more time than the smaller rings to respond to an accelerating force.
During earthquakes, two buildings of different sizes may respond very differently to the earth’s vibrations depending on how well each building’s resonant frequencies match the "forcing" frequencies of the earthquake, Of course, a building’s stiffness - which is determined by the manner of construction and the materials used—is just as important as a building’s size
Closed pipe.
Materials: A vacuum cleaner tube or golf tube. A cardboard tube may work.
Procedure:
Hold the tube against the ear and listen for any sound. Then move it away from the ear a fraction of an inch; the same sounds have a higher pitch.
Outcomes:
This is the pipe organ principle. Resonant sound vibrations in a tube closer by the ear have a lower pitch than the vibrations in a tube that has both ends open, even though it is the same length. The sounds come from the environment, just like the sounds that seem to come from a seashell.
Resonant frequency
Materials: An Oatmeal box, a sharp knife, sand.
Procedure:
Cut a hole in the side of the box 2 inches from the end. Put a few pinches of sand on the end of the box. Hold the box to the mouth and hum into the hole. Begin with high notes and go down the scale. At one point, the grains of sand will dance up and down violently.
Outcomes:
The end of the box has a natural vibration rate called the resonant frequency. When the voice sound is that frequency, it sets the box lid vibrating. Other frequencies do not make the lid vibrate appreciably.
Physical Science Materials Vendor List
Operation Physics Supplier
Arbor Scientific
P.O. Box 2750
Ann Arbor, Michigan
48106-2750
1-800-367-6695
Astronomy
Learning Technologies, Inc.
Project STAR
59 Walden Street
Cambridge, MA 02140
1-800-537-8703
The best diffraction grating i've found
Chemistry
Flinn Scientific Inc.
P.O. Box 219
Batavia, IL 60510
1-708-879-6900
Discount Science Supply (Compass)
28475 Greenfield Road
Southfield, Michigan 48076
Phone: 1-800-938-4459
Fax: 1-888-258-0220
Educational Toys
Oriental Trading Company, Inc.
P.O. Box 3407
Omaha, NE 68103
1-800-228-2269
Laser glasses
KIPP Brothers, Inc.
240-242 So. Meridian St.
P.O. Box 157
Indianapolis, Indiana 46206
1-800-832-5477
Rainbow Symphony, Inc.
6860 Canby Ave. #120
Reseda, California 91335
1-818-708-8400
Holographic stuff
Rhode Island Novelty
19 Industrial Lane
Johnston, RI 02919
1-800-528-5599
U.S. Toy Company, Inc.
1227 East 119th
Grandview, MO 64030
1-800-255-6124
Electronic Kits
Chaney Electronics, Inc.
P.O. Box 4116
Scottsdale, AZ 85261
1-800-227-7312
Electronic Kits
Mouser Electronics
958 N. Main
Mansfield, TX 76063-487
1-800-346-6873
All Electronics Corp.
905 S. Vermont Av.
Los Angeles, CA 90006
1-800-826-5432
Radio Shack
See Local Stores
Lasers
Metrologic
Coles Road at Route 42
Blackwood, NJ 08012
1-609-228-6673
Laser pointers
Magnets
The Magnet Source, Inc.
607 South Gilbert
Castle Rock, CO. 80104
1-888-293-9190
Dowling Magnets
P.O. Box 1829/21600 Eighth Street
Sonoma CA 95476
1-800-624-6381
Science Stuff - General
Edmund Scientific
101 E. Gloucester Pike
Barrington, NJ 08007-1380
1-609-573-6270
Materials for making telescopes
Marlin P. Jones & Associates, Inc
P.O. Box 12685
Lake Park, Fl 33403-0685
1-800-652-6733
Natural Wonders
Nature Store
Flea Markets
Garage Sales
Bibliography
Brown, Bob. Science for you, 112 Illustrated Experiments. Pennsylvania: Tab Books Inc., 1988.
Esler, William K. Modern Physics Experiements for the High School. New York: Parker Publishing Company, Inc., 1970.
Herbert, Don. Mr. Wizard’s Science Secrets. New York: Hawthorn Books, Inc., 1965.
Joseph, Alexander, et al., Teaching High School Science: A Sourcebook for the Physical Sciences. New York: Harcourt, Brace & World, Inc., 1961.
Liem, Tik L. Invitations to Science Inquiry. California: Science Inquiry Enterprises, 1990.
Lynde, Carleton John, phd. Science Experiments with Ten - Cent Store Equipment. New Jersey: D. Van Norstrand Company, Inc., 1950.
Rudy, Lisa Jo. The Ben Franklin Book of Easy & Incredible Experiments. John Wiley & Sons, Inc., 1995.
Science Snackbook. Exploratorium Teacher Institute, 1991.
Scienceworks. Ontario: The Centennial Centre of Science and Technology, 1984.
Unesco. Scource Book for Science Teaching. France: Unesco, 1962.
-----------------------
Record
.2-sec.
.2-sec.
.2-sec.
Slide Control
MirrorORr
.2-sec.
Figure C 12/.20= 60
Figure B 2/.18 = 11.11
Figure A 0/0 = 0
.2-sec.
.2-sec.
.2-sec.
Figure D 8/.18 = 44.44
.2-sec.
.2-sec.
Figure F 6/.13 = 46.15
Figure E 12/..20 = 60
Figure I 16/.20 = 80
Figure H 4/.18 = 22.22
Figure G 4/.17 = 23.53
Unknown 1 2,250 vib/sec
Unknown 2 2,800 vib/sec
Laser Support
Laser
[pic]
Balloon
The MAPs Team
Meaningful Applications Of Physical Sciences
Dr. Michael H. Suckley
Mr. Paul A. Klozik
Materials in this manual are based upon the Operation Physics program funded in part by the National Science Foundation. All material in this book not specifically identified as being reprinted from another source is protected by copyright. Permission, in writing, must be obtained from the publisher before any part of this work may be reproduced in any form or by any means.
Participants registered for this workshop have permission to copy limited portions of these materials for their own personal classroom use.
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