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

Waves and Their Properties

Students explore the basic properties of waves, including amplitude, wavelength, frequency, and speed, and differentiate between transverse and longitudinal waves.

• Common Core State Standards
• MS-PS4-1

About This Topic

Waves carry energy from one place to another through a repeating disturbance in matter or electromagnetic fields. In 7th grade, students explore the key properties that describe all waves: amplitude (height of the disturbance), wavelength (distance between repeating points), frequency (cycles per second), and wave speed. MS-PS4-1 specifically asks students to use mathematical representations to describe the relationship between the speed, wavelength, and frequency of a wave.

US students encounter waves in two distinct forms. Transverse waves, like light waves and waves on a rope, move matter perpendicular to the direction of energy travel. Longitudinal waves, like sound waves, compress and expand matter parallel to the wave's direction. Learning to recognize and model both types gives students the conceptual framework they need for every wave topic that follows, from sound to light to seismic waves.

Wave properties are abstract but become much more accessible when students can physically generate and measure them. Active learning approaches that have students create waves with their bodies or with slinkies and then connect those experiences to mathematical relationships help bridge the gap between the physical sensation of a wave and the numbers on a graph.

Key Questions

1. Differentiate between transverse and longitudinal waves using examples.
2. Analyze how changes in wave properties affect the energy carried by a wave.
3. Construct a model to represent the relationship between wavelength, frequency, and wave speed.

Learning Objectives

• Differentiate between transverse and longitudinal waves, providing at least two examples for each.
• Calculate the speed of a wave given its wavelength and frequency using the formula v = λf.
• Analyze how changes in amplitude relate to the energy transferred by a wave.
• Construct a model demonstrating the relationship between wavelength, frequency, and wave speed.

Before You Start

Introduction to Motion and Forces

Why: Students need a basic understanding of how objects move and the concept of speed before exploring wave motion.

Properties of Matter

Why: Understanding that waves travel through a medium (matter) is essential for differentiating between wave types and their interactions.

Key Vocabulary

Transverse Wave	A wave in which the particles of the medium move perpendicular to the direction the wave is traveling. Light waves are an example.
Longitudinal Wave	A wave in which the particles of the medium move parallel to the direction the wave is traveling. Sound waves are an example.
Wavelength (λ)	The distance between two consecutive corresponding points on a wave, such as from crest to crest or trough to trough.
Frequency (f)	The number of complete wave cycles that pass a point in one second, measured in Hertz (Hz).
Amplitude	The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position.
Wave Speed (v)	The distance a wave travels per unit of time, calculated by multiplying wavelength by frequency (v = λf).

Watch Out for These Misconceptions

Common Misconception

Waves move matter from one place to another.

What to Teach Instead

Waves transfer energy, not matter. The particles of the medium move around their original position but do not travel with the wave. The slinky lab makes this clear because the individual links return to where they started while the energy pulse moves down the spring.

Common Misconception

Louder sound waves travel faster than quieter ones.

What to Teach Instead

Amplitude (loudness) does not affect wave speed in the same medium. Only the medium and its properties (like density and elasticity) determine speed. Students who measure wave speed at different amplitudes in the slinky lab find the speed stays constant, which often surprises them.

Active Learning Ideas

Simulation Game: Human Wave Modeling

Students stand in a line and create a transverse wave by passing a slow sideways movement down the line, then a longitudinal wave by stepping together and apart. A small group with a stopwatch measures the speed of the disturbance for different amplitudes and frequencies, and the class discusses which properties changed and which stayed constant.

25 min·Whole Class

Inquiry Circle: Slinky Wave Lab

Pairs stretch a slinky across the floor and take turns generating transverse and longitudinal waves. They measure the wavelength for different frequencies by counting the visible loops and calculating speed using the frequency-wavelength relationship, then compare measurements to find the wave speed.

40 min·Pairs

Think-Pair-Share: What Changes When You Turn Up the Volume?

Students listen to two audio clips (same tone, different volumes) and two clips (same volume, different pitches). Partners identify which wave property changed in each case and sketch what the wave looked like before and after, then the class constructs a table connecting sound properties to wave measurements.

15 min·Pairs

Gallery Walk: Matching Properties to Wave Diagrams

Station cards each show a labeled or unlabeled wave diagram. Students rotate with a recording sheet, identifying amplitude, wavelength, and period for each diagram and placing the wave in order from highest to lowest energy. Groups compare answers at a final compare station.

30 min·Small Groups

Real-World Connections

• Seismologists use their understanding of wave properties, specifically how seismic waves (longitudinal and transverse) travel through Earth's layers, to map underground structures and predict earthquake behavior.
• Audio engineers adjust the frequency and amplitude of sound waves produced by speakers to create specific listening experiences in concert halls or recording studios.
• Medical professionals use ultrasound technology, which relies on the properties of sound waves, to create images of internal body structures for diagnosis.

Assessment Ideas

Quick Check

Provide students with a diagram of a transverse wave. Ask them to label the amplitude and wavelength. Then, present a scenario: 'If a wave has a frequency of 10 Hz and a wavelength of 0.5 m, what is its speed?'

Discussion Prompt

Pose the question: 'Imagine you are designing a system to send signals through water. How would you change the wavelength and frequency to send more energy? How would you change them to send a signal further?' Facilitate a discussion comparing student ideas.

Exit Ticket

On one side of an index card, have students draw and label a longitudinal wave. On the other side, ask them to write the formula for wave speed and define each variable in the formula.

Frequently Asked Questions

What are the basic properties of waves in 7th grade science?

The four key wave properties are amplitude (the height of the wave, related to its energy), wavelength (the distance from one crest to the next), frequency (the number of waves passing a point per second), and wave speed (how fast the wave moves through a medium). These properties are related by the wave speed equation: speed equals frequency times wavelength.

How does active learning help students understand wave properties?

Wave properties involve a cluster of related concepts that can blur together when read from a text. Hands-on slinky labs and body-wave simulations give students direct control over each variable. When students physically increase the frequency and observe the wavelength shrink while speed stays constant, they internalize the mathematical relationship in a way that diagrams alone cannot provide.

What is the difference between transverse and longitudinal waves?

In a transverse wave, the medium moves perpendicular (at right angles) to the direction the wave travels. In a longitudinal wave, the medium moves parallel to the wave's direction. Waves on a rope are transverse; sound waves are longitudinal.

What is the relationship between wavelength, frequency, and wave speed?

Wave speed equals frequency multiplied by wavelength (v = f x wavelength). This means that if the speed in a medium is fixed, increasing frequency will decrease wavelength proportionally, and vice versa.