Wave amplitude is the maximum distance the particles of a medium move from their resting positions as the energy of a wave passes through them. Wavelength is the distance between two corresponding points of adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Waves with greater amplitude, shorter wavelength, or higher frequency have greater energy. Wave speed is calculated as wavelength multiplied by wave frequency. It is affected by the medium through which a wave travels.
- MCR.6-8.SCI.9.7, 8; MCR.6-8.SCI.12.7
- AAAS.6-8.4.F.5, 8; AAAS.6-8.12.D.4, 6, 11
- Define wave amplitude and wavelength.
- Relate wave speed to wave frequency and wavelength.
hertz (Hz):SI unit of wave frequency, where 1 hertz equals 1 wave passing a fixed point per second
wave amplitude: maximum distance the particles of a medium move from their resting positions when a wave passes through
wave frequency: number of waves that pass a fixed point in a given amount of time
wavelength: distance between two corresponding points of adjacent waves, such as the distance between two adjacent crests of a transverse wave
wave speed: how far a wave travels in a given amount of time; calculated as wavelength multiplied by wave frequency
Introducing the Lesson
Begin the lesson by showing students waves of different amplitudes. You can generate transverse waves in a rope or longitudinal waves in a spring toy. Whichever you do, try to keep the frequency (and wavelength) of the waves the same so that only their amplitudes vary. Challenge students to explain how and why the waves differ. Tell students they will learn about this and other ways that waves may vary when they read this lesson.
Suggest that students simulate waves with different amplitudes and wavelengths with the animation at the URL below.
Visual and English language learners may have a better understanding of wave amplitude and frequency by interacting with the animation at the following URL. They can change the amplitude and frequency of ocean waves and see how the waves affect a boat floating on the water. An animated graphic of the wave also forms as they watch.
The activity at the URL below allows students to investigate wave frequency and amplitude using real-time data from various global agencies monitoring tsunami activity. In the activity, students also develop a "preparedness plan" using evidence from the data they collect.
Have groups of students do the guided inquiry activity at the first URL below to learn about wave amplitude, wavelength, and wave frequency. In the activity, they will use a simulation of a wave in a string (see second URL below).
Students may hold the misconception that “big” (high-amplitude) waves travel more quickly than “small” (low-amplitude) waves in the same medium. Explain why wave speed does not depend on wave amplitude, but instead is a product reflection of wavelength and wave frequency.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Check students’ mastery of the lesson with Lesson 19.2 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
You read in this lesson that waves travel at different speeds in different media.
- When a wave enters a new medium, it may speed up or slow down. What other properties of the wave do you think might change when it enters a new medium?
- What if a wave reaches a type of matter it cannot pass through? Does it just stop moving? If not, where does it go?