Making Waves

Before sending the students to rotate through hands-on lab and demo stations, lead them in a shared class-wide activity.

Paraphrase:

The human body is equipped to make and sense sound vibrations. In this activity, we're going to make some qualitative observations about the sound we make when we talk and sing.

Lead students as they do this simple demo.

Touch the front and sides of your throat with one to three fingers and hum or sing a note until you find the spot where you can most easily feel the vibration of your vocal cords.

Change the pitch of your hum and repeat step. Try a high note (like “eeee!”) and a low note (like “OOOO!”)

• at a normal volume
• loudly
• quietly

Show the slide with the Turn and Talk questions. Direct students to write their answers to the questions in their lab books (as they will at the sound stations).

Next, watch the looping animation (showing someone talking and someone hearing that person) with the class. Students can draw a diagram like the one shown in the animation in their lab books.

Ask the students to answer the questions in the slide.

Possible answers:

When we hear, our ears are picking up patterns of compression waves in the air.

Vocal cords vibrate to generate sound waves that are our voice. The vocal cords change shape to produce distinct tones that are further shaped and amplified by the throat and mouth.

The speakers receive an electrical signal that vibrates a magnet at the base of the speaker. The diaphragm in the speaker vibrates and compresses the air molecules around it. The compression of those air molecules creates a vibration, or sound wave, which then travels through the air to your ear. It’s like molecules bumping into each other all the way from the speaker to your ear!

You can expand on the anatomical mechanisms of the ear:

While we think of our ears as organs of hearing, the fine hairs are actually very tiny touch sensors that sense movement in the fluid of the cochlea, the curled canal inside the inner ear.

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When you hear a sound, what are you actually hearing?

How are sound waves of the human voice generated?

How are sound waves received by the human ear?

When you listen to music, have you ever thought about how your favorite song gets from the speakers to your ear? How does this model change when we're listening to music from a stereo?

This special applet can be used for a lot of free exploration. Rather than use it for a five-minute sound station, you may opt to use it with your whole class for some inquiry-based learning beyond the explorations outlined here.

Note: we were inspired by two demos on Academo: the virtual oscilloscope and amplitude modulation. If you have technical issues with our embedded applet, you can use these online demos to cover much of the station's exploration. If using Academo's amplitude modulation app, be sure to turn on the sound and slide A2 all the way down to 0.0, and use the f1 slider only.

Paraphrase:

Scientists and engineers use a tool called an oscilloscope to compare different waves, including sound waves. The "oscillo-" part of the word means "swing," just as in the word "oscillate."

Musicians don't usually pay any attention to the shape of the waves, but this special instrument makes sound, lets you see the wave as a physicist would see it, and then lets you play around with a note.

Materials

• Electronic device (such as a computer, tablet, or mobile phone) with this app loaded (online or saved locally)
• Microphone that can be plugged into the computer (optional)

About oscilloscopes

The teal window of the applet emulates what one would see if an oscilloscope were next to a keyboard. An oscilloscope is a tool physicists use to analyze the quality of sounds and many other kinds of waves. Because an oscilloscope shows the shape of a wave with a repeating pattern, some assume that what they see on the screen is the actual shape of the wave produced by the different notes, but this assumption is not correct. Instead, the oscilloscope shows a graph of the changing pressure of the sound wave. That is, sound is a compression wave, so it would not look like a sine wave or for that matter, a square, triangle, or sawtooth wave.

Think of another electronic tool you may have seen in the hospital or in a medical drama: the EKG or electrocardiogram. The graph seen on that screen is not a picture of the heartbeat, but a graphical representation of a heartbeat, one which health professionals use to get a snapshot of a patient's well-being. It is showing electrical pulses from the heart.

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Materials

• 7 straws (with 6 mm diameter)
• masking tape
• centimeter ruler
• permanent marker

Paraphrase:

Every sound is made when something vibrates. Sometimes it's the skin stretched across a drum, sometimes it's a plucked string. By fine tuning the amount of what is vibrated, you can make notes. At this station you'll make a full octave of eight notes.

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Materials

• 8 identical tall, thin glasses or jars, preferably with vertical sides.
• pitcher or bucket with at least 6 cups of water
• pencil or wooden dowel to use as a mallet
• ruler
• towel for mopping up small spills (optional, but recommended!)

Paraphrase:

Every sound is made when something vibrates. Sometimes it's the skin stretched across a drum, sometimes it's a plucked string. By fine tuning the amount of what is vibrated, you can make notes. At this station you'll make a full octave of eight notes.

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Materials

• 2 cups
• 6 meters of string
• scissors
• nail (or other device for poking a small hole)

Paraphrase:

Sound waves are mechanical waves; they need a medium to transmit energy. When we clap our hands, the air between our hands gets compressed. The air molecules bump into each other, creating a vibration that travels through the air as a longitudinal or compression wave.

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Preparation

1. Measure and cut a 6-meter length of string.
2. Using the nail, poke one small hole in the bottom of each cup.
   
   
3. Feed the string through the bottom of each cup and tie a large knot so that the string cannot pull out.
   
   
4. After making a phone with a 6-meter length of string, you might try different lengths of string so students can see how the length affects the effectiveness of the phone.

Students may be familiar with the sound heard from a passing car whose stereo has the bass set so high and the volume so loud that the neighborhood windows shake. A similar transfer of energy is easy to see with a small boom box and some pepper sprinkled on paper.

For a more ambitious demo, consider building a Chladni Plate or at least watching a video of them in action.

Materials

• media player with a decently loud speaker (such as a boom box)
• balloon
• paper plate
• pepper

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Materials

• metric ruler

Paraphrase:

Every sound is made when something vibrates. Sometimes it's the skin stretched across a drum, sometimes it's a plucked string. By fine tuning the amount of what is vibrated, you can make notes of different pitches. Students adjust the pitch of a simple musical instrument by changing the amount of freely moving wood that gets plucked.

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Add other optional sound stations if you have the materials for these higher-end physics demos: tuning forks and resonance boxes.

Caution the students to use the tuning forks gently:

Do your best to avoid dropping your tuning forks. They are very easy to break. They are very delicate. Hold them only by the handle, and strike them only against rubber: if you don't have a sounding block, some science teachers and their students have used the sole of their shoe as a striking surface.

Materials

• up to 4 tuning forks
• rubber or soft wooden block for striking tuning forks (important: forks break easily when struck against hard surfaces)
• table tennis ball (usually known as a "Ping Pong® ball") attached to about 1 foot (30 cm) of string and hanging from a stand or off the side of a table where it can move freely
• 2 resonance boxes
• weight
• ruler (optional—for measuring an approximate distance)
• a shallow tray of water (like a food service container)

Paraphrase:

Resonance boxes and tuning forks make it possible to hear a usually undetectable phenomenon: waves transferring energy from one medium to another. They can be quite expensive, however, and you may be able to demonstrate a similar phenomenon by simply bringing the vibrating end of a tuning fork close to the surface of some water, and touching it to the surface.

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Ask:

What did the different stations have in common? How were they different?

Paraphrase:

Musical instruments, including those we used today, produce sounds when some part of them is vibrated.

Ask:

What is vibrating when these instruments make sound?

• clarinet (the reed)
• trumpet (the lips of its player)
• drum (its head)
• flute (the air inside the flute)
• piano (strings inside the body of the piano that the hammers hit)
• guitar (strings)
• violin (strings)

What's vibrating?

clarinet

trumpet

drum

flute

piano

guitar

violin