Science · 7th Grade · Energy and Matter in Motion · Weeks 1-9

Sound Waves

Students investigate the production, transmission, and perception of sound, exploring how sound waves interact with different media.

• Common Core State Standards
• MS-PS4-2

About This Topic

Sound is a longitudinal mechanical wave that requires a medium to travel. It is produced by vibrating objects that create compressions and rarefactions in the surrounding matter. MS-PS4-2 asks students to develop and use models to describe the ways wave properties can be used to describe a sound's characteristics: amplitude corresponds to loudness and frequency corresponds to pitch.

US 7th graders build a solid understanding of sound by connecting their everyday auditory experiences to the wave model. The pitch of a guitar string relates directly to how fast it vibrates. The volume of a speaker relates to how far it moves the air. Students also explore how the speed of sound changes in different media: sound travels faster through denser materials like water and solids than through air, which leads to counterintuitive but memorable results.

Sound is a strong entry point for active learning because students can feel vibrations physically and make direct measurements using inexpensive or digital tools. Investigations that connect what they hear to what they can measure create a strong feedback loop between experience and understanding.

Key Questions

1. Explain how vibrations create sound waves.
2. Compare the speed of sound in different states of matter.
3. Analyze how the properties of a sound wave relate to its pitch and loudness.

Learning Objectives

• Develop and use models to describe how vibrations produce sound waves, including compressions and rarefactions.
• Compare the speed of sound through different states of matter (solids, liquids, gases) using experimental data.
• Analyze how the frequency of a sound wave relates to its perceived pitch.
• Analyze how the amplitude of a sound wave relates to its perceived loudness.
• Explain how sound waves are produced and transmitted through a medium.

Before You Start

Properties of Waves

Why: Students need a basic understanding of wave motion, including concepts like crests and troughs, to grasp compressions and rarefactions.

States of Matter

Why: Understanding the particle arrangement and movement in solids, liquids, and gases is essential for comparing the speed of sound in different media.

Key Vocabulary

Vibration	A rapid back-and-forth movement of an object that produces sound.
Sound Wave	A longitudinal mechanical wave that travels through a medium, consisting of compressions and rarefactions.
Medium	The substance or material (solid, liquid, or gas) through which a wave travels.
Frequency	The number of complete wave cycles that pass a point in one second, measured in Hertz (Hz), and related to pitch.
Amplitude	The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position, related to loudness.

Watch Out for These Misconceptions

Common Misconception

Sound travels faster through air than through water or solids.

What to Teach Instead

Sound actually travels faster through water and much faster through metals like steel than through air because the particles are closer together and pass vibrations more efficiently. Students who test sound transmission through a desk versus through air find this counterintuitive result memorable and compelling.

Common Misconception

Higher pitched sounds are louder.

What to Teach Instead

Pitch (frequency) and loudness (amplitude) are independent wave properties. A high-pitched whisper can have less amplitude than a low-pitched shout. Sketching and comparing wave diagrams where amplitude and frequency are varied independently helps students keep these concepts separate.

Active Learning Ideas

Inquiry Circle: Tuning Fork and Water

Groups strike a tuning fork and touch the tines to a shallow dish of water, observing the waves created on the surface as evidence that the fork is vibrating. Students then hold the vibrating fork at different distances from their ear to describe how amplitude (loudness) decreases with distance.

30 min·Small Groups

Stations Rotation: Sound Through Different Media

At station one, students tap a wooden desk quietly and listen from a short distance. At station two, they place one ear on the desk and tap at the same force. At station three, they use cups connected by string. Students compare perceived loudness at each station and explain the differences using wave speed and energy transfer through different media.

40 min·Small Groups

Think-Pair-Share: Pitch vs. Loudness

Play audio clips of the same instrument at different pitches and volumes. Students individually sketch the wave they think matches each sound, then compare sketches with a partner and discuss which property (frequency or amplitude) changed. The class assembles a set of canonical wave diagrams for high/low pitch and high/low volume.

20 min·Pairs

Inquiry Circle: Musical Straw Instruments

Groups cut plastic straws to different lengths and blow across them to produce sounds. They measure the straw lengths, listen to the pitches, and graph length versus pitch to establish the relationship between the length of a vibrating air column and the frequency of the sound produced.

35 min·Small Groups

Real-World Connections

• Acoustic engineers design concert halls and recording studios to control sound reflection and absorption, ensuring optimal sound quality for musicians and audiences.
• Sonar technicians use sound waves to detect objects underwater, mapping the ocean floor and locating submarines or shipwrecks for the U.S. Navy and research vessels.
• Musical instrument makers carefully select materials and shapes to produce specific pitches and volumes, understanding how vibrations travel through wood, metal, or strings.

Assessment Ideas

Quick Check

Present students with images of different musical instruments (e.g., a guitar, a drum, a flute). Ask them to write one sentence explaining how each instrument produces sound waves and one sentence describing how they might change the pitch or loudness.

Discussion Prompt

Pose the question: 'Imagine you are trying to send a message to a friend across a swimming pool. Would you shout, whisper, or tap on the side of the pool? Explain your choice using the terms 'medium,' 'speed of sound,' and 'amplitude.'

Exit Ticket

Give each student a card with a scenario. For example: 'A loud clap of thunder is heard.' Ask them to write: 1. What is vibrating to create the sound? 2. What medium is the sound traveling through? 3. Does the sound wave have a high or low frequency (pitch)? Does it have a large or small amplitude (loudness)? Explain why.

Frequently Asked Questions

How are sound waves produced and transmitted?

Sound is produced when an object vibrates, creating a series of compressions (areas of high pressure) and rarefactions (areas of low pressure) in the surrounding medium. These pressure variations travel outward as a longitudinal wave until they reach a listener's ear.

How does active learning help students understand sound waves?

Sound is already experiential, and active learning capitalizes on this by connecting those experiences to measurements. When students feel a vibrating tuning fork, observe its effect on water, and then map that to a wave diagram, they build a chain of understanding from sensation to model that is far more durable than memorizing a definition of frequency.

How does the speed of sound change in different materials?

Sound travels faster in denser materials where particles are tightly packed. Steel transmits sound at about 5,100 m/s, water at 1,480 m/s, and air at about 343 m/s. This explains why you can hear a train approaching through the rail long before you hear it through the air.

What determines the pitch and loudness of a sound?

Pitch is determined by frequency: how many times the source vibrates per second. Higher frequency means higher pitch. Loudness is determined by amplitude: how far the medium is displaced during each compression. Greater amplitude means a louder sound.