Tag - sound

Wind Instruments Inquiry

Simple instruments to explore sound and frequency.

Students will use three simple toy instruments to explore fundamentals of sound and frequency in this inquiry exercise. Boomwhackers: Students will share a number of colored plastic tubes of various lengths. Standing sound waves are excited inside the tubes, with wavelengths a little longer than double the length of the tube. Twirling Pipes: When the sound pipes are twirled around, they produce a note whose pitch depends upon how fast you can twirl it! You can probably produce only three different pitches, or frequencies. The pipes are producing members of a harmonic series. Students will also make soda straw flutes.

Required Equipment
Boomwhackers, Audioscope software or Sound Sensor for measuring frequency, Sound Pipe, Soda Straws, Scissors.

Acknowledgements: Thank you to Dr. J.R. Harkay author of Phenomenal Physics for providing this student inquiry activity. Adapted from “Pythagoras Sounds Off II: Wind Instruments,” an Inquiry Exercise by J. R. Harkay.  Seewww.PhenomenalPhysics.com for more information on the complete Guided Inquiry Curriculum.

Dr. Russell Harkay
Keene State College
New Hampshire

The “Sound Sensor” required for this lab is readily available at your local music store as an instrument tuner with a built in microphone. Korg electronic tuners (about $20) make wonderful frequency meters! Each lab group would need one sound sensor.

Download Teacher Notes and Student Worksheets

Set of 8 Boomwhackers

In Stock SKU: P7-7400
$34.00

Sound Pipe

In Stock SKU: P7-7200
$2.95

The “Sound Sensor” required for this lab is readily available at your local music store as an instrument tuner with a built in microphone. Korg electronic tuners (about $20) make wonderful frequency meters! Each lab group would need one sound sensor.

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Doppler Effect

subway passing
The Doppler Effect occurs when an observer hears a sound from a moving source. If the sound source is moving toward the observer, the perceived frequency will be higher than the actual sound frequency. If the source is moving away from the observer, the perceived frequency will be lower.

Required Equipment
Doppler Ball, and String

Download Teacher Notes and Student Worksheets

Doppler Ball

In Stock SKU: P7-7120
$15.00

Roll of String

In Stock SKU: PX-2134
$3.90
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Lab #26.9 Sound: Sound Off

Purpose
In this activity, students will hear a dramatic effect of the interference of sound.

Discussion
Interference is a behavior common to all waves. With water waves we see it in regions of calm where overlapping crests and troughs coincide. We see the effects of interference in the colors of soap bubbles and other thin films where reflection from nearby surfaces puts crests coinciding with troughs. In this activity we’ll dramatically experience the effects of interference with sound!

Required Equipment

Stereo radio, tape, or CD player with two moveable speakers, one of which has a DPDT (double pole double throw) switch or a means of reversing polarity (such as switching red and black wires).

Download

Student Worksheet   Teacher Notes

Knife Switch, Double Pole, Double Throw

In Stock SKU: P6-7108
$3.95

The “Speakers” required for this lab are available from Radio Shack or can be salvaged from old stereo speaker systems. Each lab group would need access to one of each see lab detail for specific use.

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Lab #26.1 Sound: Slow Motion Wobbler

Purpose
In this activity, students will observe and explore the oscillation of a tuning fork.

Discussion
The tines of a tuning fork oscillate at a very precise frequency. That’s why musicians use them to tune instruments. In this activity, you will investigate their motion with a special illumination system— a stroboscope.

Required Equipment
Low-frequency tuning forks (lower frequency forks work best for large amplitudes), bright strobe light with a widely variable frequency.

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Student Worksheet   Teacher Notes

Tuning Fork 256Hz Note C

In Stock SKU: P7-5100
$8.50

Pulsar Strobe Light

In Stock SKU: P2-9005
$39.00
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Sound & Waves: Good Vibrations Part 1

Good Vibrations An Exploration of Vibration, Sound, and Music

A wave is a disturbance that transports energy from one place to another without the transfer of matter. After a wave passes through a medium, there are no residual effects; the medium remains unchanged. For example, if you throw a stone in a pond, a circular wave will spread out from the point of impact. If the wave encounters an object floating in the water, the object will briefly bob up and down. However, once the wave has passed, the object, and the water that buoys it up, will be left undisturbed.

We encounter waves everyday. Some are apparent; others go unnoticed. The room in which you are sitting is being criss-crossed by all sorts of waves. These include light waves, radio waves, and sound waves. While we have receptors for light and sound, our bodies are not capable of sensing radio waves directly. Some waves, such as sound and water waves, require a material medium. On the other hand, light and other forms of electromagnetic radiation can travel through the vacuum of space.

A fascinating feature of waves is that two of them, traveling in opposite directions, can pass right through each other and emerge with their original identities. However, while the pulses overlap, the height at any point is simply the sum of the displacements due to each pulse itself. If the pulses are on the same side of the medium they add; if they are on opposite sides, they subtract. This is called interference.

The importance of wave phenomena in everyday life cannot be overstated. It is estimated that human beings receive over 90% of their information from light and sound. The experiments that follow will allow you to gain first hand experience with the properties of waves in general and sound in particular.

Student Activities

1. Working with Waves

Key Concept:
A wave is a disturbance that travels through a medium. Waves are characterized by wavelength, frequency, and amplitude. Waves reflect when they encounter a barrier or different medium.

A rope or a long spring may be used to demonstrate many properties of waves. Hold one end of the stretched medium in your hand while your partner holds the other end. Now move one end up and down at different rates (frequencies). What happens to the wavelength as you increase the frequency? Decrease the frequency?

Does the tension in the medium have any observable effect on the speed of a wave? To find out, send a sharp pulse down the medium when the medium is under various degrees of tension. What do you observe?

Send another sharp pulse down the medium. This time watch carefully as the pulse reaches the fixed end. Does the pulse reflect? If so, is the reflected pulse the same as the incident pulse or is it upside down? Do the incident and reflected pulses travel at the same speed?


Helical Spring “Snaky”

Helical Spring

In Stock SKU: 33-0140
$19.50

Super Springy

In Stock SKU: 33-0130
$12.95

2. The Unusual Way of Waves

Key Concept:
The overlapping, or superposition, of two waves produces reinforcement in some instances and cancellation in others.

You can witness wave interference on a phone cord, rope, or Slinky. After producing one pulse on the medium, generate a second shortly thereafter. Watch carefully as the two pulses meet and pass through one another. How would you describe the medium when the two pulses overlapped? Did the pulses produce a larger or smaller resultant pulse? What procedure must you follow to produce constructive interference (a larger net pulse)? Destructive interference (a smaller net pulse)?

3. Nice Nodes

Key Concept: 
Standing waves are formed when two sets of identical waves pass through a medium in opposite directions.

Move the end of the medium of choice (rope, phone cord, Slinky) up and down at the right frequency to create a full wave. When this has been accomplished you will notice that the center of the medium appears to stand still. This stationary point is called a node. At a node, the destructive interference of the incident and reflected waves is total. On either side of the node are regions of maximum displacement called antinodes. Have someone gently pinch the node with their fingers. What happens?

Increase the frequency of the up and down motion of your hand until two nodes appear on the medium. How many antinodes are there now? How many wavelengths do you observe? What happens when you continue to increase the frequency of the waves? Can you obtain three nodes, four nodes, etc.? Describe what happens to the wavelength as the frequency is increased.


Standing Wave Kit (10pk)

In Stock SKU: P6-7700
$55.00

4. Are You Chicken?

Key Concept:
A surface set in motion by a vibrating string amplifies sound.

Using a toothpick, puncture a small hole in the center of the base of a paper or plastic cup. Pull a ½ meter, or so, length of string through the hole. With the cup turned upside down, tie the string around the toothpick (see figure).

Rub a little rosin on your thumb and index finger. Using a jerking motion, pull down on the string while gently pinching it between the thumb and index finger. Describe what you hear as the string moves between the fingers.

What is the source of the sound you hear? Why is the sound so loud? To answer this question, it may be helpful to pull on the string when it is not connected to the cup.

What’s it sound like?

5. The Singing Rod

Key Concept: 
Longitudinal standing waves may be produced in metal rods.

Hold the aluminum rod with your fingertips at its center. (Note: The center may be located by balancing the rod in your hand in the region between the thumb and index finger as in the figure above.) Place some rosin on the tips of the thumb and index finger of the other hand. Grip one end of the rod between the rosin-covered fingertips and stroke the length of the rod between the end and center.  With a little practice, you should be able to produce a piercing, high-pitched sound. If you are unable to get the rod to sing, tap the end of the rod with a mallet or hammer or tap it on a hard surface.

While the rod is “singing,” bring a ping pong ball suspended on a string in contact with an end of the rod.  Describe what happens. Can you explain why this occurs?  What did stroking or tapping the rod do to it? Grab the singing rod at a point off center. What happens?  Why?

Singing Rods (Set of 2)

In Stock SKU: P7-7250
$19.00

6. The Bells of St. Weber

Key Concept:
The grate’s small surface area prevents efficient energy transfer to the air at low frequencies. The strings provide a direct pathway for sound transmission at a wide range of frequencies.

Pick up the grate from a barbecue grill by the strings. ( If you don’t have a clean grill grating, coat-hanger or metal utensils work too!) With the grate hanging by the strings, knock it against the side of a table. Describe the sound you hear.
How does the sound produced by the vibrating grate reach your ears?

Now, with your index fingers, place the ends of the strings on the little flap of flesh that protrudes over the opening of each ear. Allowing the grate to hang freely from the strings, again swing the grate into the side of a table. Describe the sound you hear with the strings pressed against your ears. How is the sound reaching your ears? How do you explain the difference in sound quality?

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Sound & Waves: Good Vibrations Part II

An Exploration of Vibration, Sound, and Music

We will demonstrate how sound waves are produced and reveal how they may be recorded and reproduced.

Among the activities below are two that introduce students to analog sound recording. Growing up in the era of digital recording, most students are amazed to learn that sound can be recorded on an old fashioned record and reproduced with nothing more than a needle and a cardboard cone. However, some students may recognize this simple device as a rudimentary Edison record player. Students of all ages never fail to be amazed to learn that a single groove in a record may contain information about a wide variety of musical instruments and singers and that our ears are capable of sorting out the individual notes and voices when a record is played.

Talkie Tapes can be thought of as linear records. However, instead of a groove, the strip is covered with ridges and pits that cause an object, such as a fingernail, to vibrate as it is dragged along the strip. As with the Edison record player, amplification is achieved by attaching the strip to an object capable of moving more air.

After completing their study of analog recording, students should be encouraged to investigate the difference between analog and digital recording processes. The Internet offers many sites that discuss the two recording techniques. Oh, and one other thing: You might want to tell students not to attempt to play their CDs with a pin! Believe me, more than one student has tried it!

Student Activities

1. The Diving Tuning Fork

Key Concept: 
A vibrating object possesses kinetic energy.

Strike the end of a tuning fork on a rubber pad or on the heel of your shoe. Barely touch the surface of a cup of water with the vibrating ends of the tuning fork.

What do you observe?

Do the vibrating ends of the tuning fork possess energy?

How do you know?

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1. Talkie Tapes

Key Concept:
Ridges embossed on the surface of this strip cause your thumbnail to vibrate. The cup, with its larger surface area, amplifies the sound.

Hold the pointed end of the plastic talking strip between the thumb and the index finger. Using your other hand, drag your thumbnail along the ridges on the strip, moving from top to bottom. Do you hear anything?

If you didn’t hear anything as you moved your thumbnail along the strip, hold the pointed end of the strip against the end of a paper or Styrofoam cup. What do you hear this time? Why was the sound louder when the cup was used?

Try using other materials (for example, a piece of paper, a windowpane, a blackboard, a balloon, your front teeth) to amplify the sound. List the amplifying materials you test and describe their effectiveness as amplifiers.

How do you suppose the strip “talks” as you drag your thumbnail across the ridges?

Can you think of any other device that produces sound in a similar manner?

3. Music Box Marvel

Key Concept: 
The music box forces the cup to vibrate. Because of its larger surface area, the cup causes more air to move. This in turn results in a louder sound.

Teacher’s Note: 
Obtain the inside mechanism from a mechanical music box. The mechanism should not have an amplifier (any type of box or platform) attached.

If necessary, gently wind the music box mechanism. Listen to the tune.

Can you identify it? Can you even hear it?

Bring the mechanism in contact with a Styrofoam or paper cup, tabletop, window, blackboard, etc. Is the sound louder when it is in contact with a solid object?

Why do you suppose this is so?

Which object(s) makes the sound the loudest?

Which objects tend to be the least effective amplifiers?

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4. Getting In The Groove

Key Concept: 
Grooves in a phonograph record cause the needle to vibrate. The cardboard cone, with its large surface area, amplifies these vibrations.

Form a cone out of a piece of poster board or file folder. Tape the edge so that the cone will retain its shape. After you place a straight pin through the tip of the cone, as is shown below, you will have an Edison-style record player.

Cradle the cone in both hands as you lower the straight pin into the groove of a spinning record. The pin should drag behind the base of the cone, with only the weight of the cone holding it down.

What do you hear?

Describe the loudness and clarity of the sound.

Explain how sound is produced with this simple record player.

Since records may be foreign to many students, it may be instructive to allow them to look at record grooves through a magnifying glass or microscope. The recorded information appears as a squiggly line that spirals in from the outer edge of the disk to the center. The nature of the grooves reveals where the recorded sound is the loudest (the squiggle is wide in loud passages) and where the sound has high frequency components (the squiggles are close together). As the needle moves through the grooves, these variations in the groove cause the needle to vibrate, producing sound. Since the needle does not displace much air as it vibrates, it’s necessary to attach the needle to the cardboard to amplify the sound.

5. Singing Tubes

Key Concept: 
As the air passes through the tube, it strikes the ridges that line the tube. Increasing the rate of twirling causes air to be drawn through the tube at a higher speed. As air speeds up, the frequency of sound produced by the air’s interaction with the tube walls also increases. However, since the length of the air column determines the frequencies that are reinforced, only certain rates of twirling will produce audible, sustainable sound.

Hold the large end of the plastic tube in one hand and swing the other end over your head. Be certain that no one is in the immediate area before you start swinging the tube. Start out swinging the tube slowly, then speed up. You should hear higher and higher pitches as you swing the tube faster and faster.

What do you think is producing the sounds you hear?

Why does increasing the rate of swings increase the pitch of the sound produced?

Can you produce any pitch you wish or are there only certain sounds that can be produced?

Now tear a sheet of paper into some small bits and place them on a tabletop. Hold the stationary end of the tube over the bits of paper while swinging the other end of the tube. Watch the paper fly!

Based on the movement of the bits of paper, which way does the air flow through the tube?


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6. The Last Straw!

Key Concept: The vibration of air in tubes is the mechanism for sound production in virtually all wind instruments. The length of the air column determines the pitch.

Pinch together about ¾” of the end of a soda straw. This may be accomplished by pulling the end of the straw through clenched teeth. Using scissors, diagonally cut off the corners of the flattened end (see figure on left).

Place the flattened end in your mouth and blow gently. With a little practice, you will discover how to adjust your lips and air pressure to allow the straw’s reeds to vibrate correctly. When the reeds vibrate, a sound will be produced. The device you have produced may be thought of as a “soda straw oboe,” because like its namesake, it uses a double reed to produce sound.

Once you have produced a clear, loud sound, cut off successive pieces of the open end of the straw.

What happens to the pitch of the sound as the straw gets shorter?

How does a real oboe achieve changes in pitch?

Make another straw oboe, but this time cut small notches along the length of the straw. The effective length of this device is changed by covering and uncovering the holes. See if you can play a tune on this oboe!

7. Tuning Fork Interference

Key Concept: 
Because each of its tines have a front and back surface, a vibrating tuning fork radiates sound from a total of four surfaces. Sound from these surfaces superimpose in the area surrounding the tines, producing an audible interference pattern.

Strike a tuning fork with a rubber hammer or on the heel of your shoe. (Please do not strike the tuning fork on the edge of the table.) Place the vibrating tuning fork near your ear. Slowly rotate the vibrating tuning fork and note any variation in the intensity (loudness) of the sound. Make certain that you rotate the tuning fork through 360 degrees.

What do you hear?

Can you explain your observation?


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8. The Domino Effect

Key Concept: 
Energy may be transferred without the transfer of mass.
Arrange as many dominoes as possible in a row. They should be placed on end and positioned so that when one topples, it will cause the next domino in line to tip over. Describe the disturbance as it passes through the dominoes.

Does it travel at a constant speed?
What do you suppose determines the speed at which the disturbance travels?
Experiment with changing the spacing between dominoes.
Does this affect the speed?

How is the domino model of wave propagation similar to a wave on a spring or the surface of water?
How is it different?
Based on your knowledge of waves, do falling dominoes correctly model wave behavior?
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