Sound

From Teaching Physics with Toys, from 101 Great Science Experiments, and from https://www.teachengineering.org/lessons/view/cub_energy2_lesson05

Learning Objectives

After this lesson, students should be able to:

• Give several examples of engineering products that involve sound.
• Describe sound as a form of energy.
• Define volume, pitch and frequency as they relate to sound energy.
• Describe sound energy as traveling in waves.
• Explain sound as a form of communication.

What is sound?

Engineering Connection

Engineers use their knowledge of sound waves to create radio and sonar devices. Sound waves traveling through the air are collected by radio antennas. Sonar devices send ultrasound waves into an ocean and create images based on which waves are bounced back to the device. Ships use sonar to navigate and map the seabed by measuring water depth. Sonar is also used to search for undersea objects such as wrecks, submarines, rocks, icebergs, whales and fish. Engineers also design instruments that "listen" to ultrasound and infrasonic sound waves. Ultrasound can detect tiny flaws in materials used to make parts — from bridge bolts to aircraft wings.

Experiment: Sounds Produced with Different Lengths of Ruler 

1. Place a 12 inch ruler flat on a table. Let 4 inches of the ruler extend over the edge of the table 
2. Hold the ruler securely to the table with one hand and pluck the other end of the ruler that sticks out over the end of the table with the other hand
3. have students duplicate  steps 1 and 2 with their own rulers
4. ask students "What did you see?" Vibration. "What did you hear?" Sound
5. have students experiment with different lengths of ruler extending over the end of the table. Point out that they are making different sounds.

Need: rulers

Experiment: Sounds Produced with Different Rubber Bands

1. Make a box guitar. Pluck rubber bands one at a time to make different sounds
2. ask students "Why are the sounds of the various bands different?" The rubber bands have different masses and are under different amount of tension. These differences contribute to different frequencies of vibration and therefore different sounds
3. Explain that the energy from a vibrating object transfers to gas particles, which pass their energy to adjacent particles, producing a wave.

Need: tins

rubber bands

Experiment: See sound by building a sound gun

Need:
thin plastic table cloth

tube

stiff paper

thin strip paper

pencil

rubber band

tape

See Sound

Introduction/Motivation - Volume, Pitch, Frequency

Have the students close their eyes and sit quietly for 30 seconds. What did you hear? (Have a few students describe the different sounds they heard.) These are all sounds and we will be learning about sound energy today.

Now tap on your desk. How would you describe that sound? Can you tap on your desk louder? Now, really softly? What do we call this change in sound? We call this characteristic of sound, volume.

Now, tap on your desk using a pencil. What is this sound like? Is it a higher sound? We call this characteristic of sound, pitch. You have just learned two of the three important characteristics of sound energy that we will discus today — sound volume and pitch.

To travel, sound energy must vibrate molecules. These molecules move in a sound wave. Sound frequency is how much a sound wave is vibrating. Frequency is the third characteristic of sound that we will discus today. Let's see what this looks like!

Classroom demonstration: Use a large spring or slinky to demonstrate the characteristic of frequency. Expand the slinky and have students hold each end. Make sure the students stand very still and do not shake the slinky.

• To describe longitudinal waves, grab a few coils of the spring and let go of them. As the students watch the waves travel through the spring, explain that these waves are longitudinal waves. Explain that the release of the coils represents the source of the sound vibration and that this sound is moving longitudinally across the slinky. Harmonic sound waves are usually longitudinal waves.
• To show transverse waves, strike the spring at right angles to its length. Have the students describe the up and down motion of the spring. Explain that this motion represents transverse waves. Radio waves are examples of transverse waves used by engineers to send messages over long distances. Transverse waves also travel on the strings of instruments, such as guitars and banjos.
• If possible, show Professor Dan Russell's excellent online animation of longitudinal and transverse waves at http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html.

Other Frequencies

Our ears pick up a wide range of frequencies. However, some animals hear frequencies that are too high-pitched for our ears to detect. These frequencies are called ultrasounds. Other creatures detect frequencies known as infrasonic sounds that are too low for our ears to detect.

To detect what our ears cannot hear, engineers design instruments that are able to "listen" to ultrasound and infrasonic sounds. Ultrasound can detect tiny flaws in metals, plastics and other materials used to make parts — from bridge bolts to airplane wings. Ultrasound used in medical sensing equipment helps us "see" the development of a baby inside its mother's womb. Ships use sonar, a type of ultrasound, to search for undersea objects such as wrecks, submarines, rocks, icebergs, whales and shoals of fish. Sonar can also measure the water depth so it is useful for ocean navigation and mapping the seabed.

Some electronic equipment built by engineers turns ultrasound or infrasonic sound signals into electrical signals, and further into sounds of lower pitch, which we can hear as "pings," or into visual patterns of lines and colors that we can see on monitor screens.

Experiment: Traveling Sound

Traveling Sound - Students explore how sound waves move through solids, liquids and gases in a series of simple sound energy experiments. They see how engineers use their understanding of the properties of sound energy when designing recording studios, libraries and concert halls.

Every sound, whether it is from a rubber band twanging or a loud speaker cone, is created by vibration. You cannot hear sound in a vacuum because sound reaches your ear as vibration, and there must be something to vibrate. Usually, the medium that vibrates is air. When the sound source vibrates back and forth, it pushes the air around it back and forth. The sound travels through the air as it is pushed back and forth in a chain reaction that is being alternately stretched and squeezed. This moving stretch and squeeze is called a sound wave.

• Can sound energy travel through solids? Students place their ears on a desk or table as they tap or scratch on the top. They compare that to the same sound made when their ear is not pressed to the table.
• Can sound energy traveling through liquids? Fill a large bowl or bucket (metal works best) with water. One student taps two spoons together under the water. Two other students observe and compare the tapping sound they hear, as heard through the air and as heard by placing an ear against the bowl.
• Can sound energy traveling through gases (air)? The students feel their throats gently during each of these tasks:

- Hum with your mouth and nose open.

- Hum with your mouth open and nose closed.

- Hum with your mouth closed and nose open.

- Hum with your mouth and nose closed.

Lesson Closure

What is sound energy? (Answer: It is the energy produced when sound is created.) What are three characteristics of sound energy? (Answer: Volume, pitch and frequency.) We may not be able to hear every sound that exists, but engineers use all types of sounds to create devices that help people. Engineers have designed instruments that can "hear" ultrasonic and infrasonic sound that humans cannot hear with their ears. Sound is a type of energy that we use every day, especially when our families, friends and our teachers talk to us.