Mechanical waves are waves that transfer energy through matter, called the medium. Types of mechanical waves include transverse, longitudinal, and surface waves. In a transverse wave, the medium vibrates at right angles to the direction that the wave travels. In a longitudinal wave, the medium vibrates in the same direction that the wave travels. A surface wave travels along the surface of a medium and combines a transverse wave and a longitudinal wave.
- MCR.6-8.SCI.9.7, 8
- AAAS.6-8.4.E.2; AAAS.6-8.4.F.5; AAAS.6-8.12.D.4
- Define mechanical wave.
- Describe transverse waves.
- Identify longitudinal waves.
- Describe surface waves.
longitudinal wave: wave in which particles of the medium vibrate in the same direction that the wave travels
mechanical wave: disturbance in matter that transfers energy from one place to another
surface wave: combined transverse and longitudinal wave that travels along the surface of a medium
transverse wave: wave in which particles of the medium vibrate at right angles to the direction that the wave travels
Introducing the Lesson
As students enter the classroom and settle into their seats, pique their interest in waves by playing a video of surfers exploiting huge ocean waves (you can choose from the videos below). While students watch the video, ask them to describe the waves and form a preliminary definition of the term wave. Tell students that they will learn about waves—including ocean waves—when they read this chapter.
You may want to use the PowerPoint presentation at the following URL to teach lesson concepts. It includes excellent visuals and incorporates a simple activity for generating transverse and longitudinal waves with a spring toy. You can have students generate the waves or you can generate them yourself while the class watches.
The kinesthetic wave activity described in the document below can be done indoors or outdoors. It is an excellent exercise for introducing students to waves. In the activity, students will line up and do “the wave” while you discuss what a wave is and other basic wave concepts. The document explains how students can vary wave measures such as wavelength and amplitude, which are covered in the next lesson, “Measuring Waves.”
Help students focus on the main concepts in the lesson by having them make a concept map for the lesson. Pairs of students can work together to make concept maps, or you can work with the class to make a concept map on an overhead transparency. A sample concept map is shown below.
Ask one or more advanced students to learn more about seismic waves and then teach the topic to the class. The URLs below are a good place to start. Tell students to use visuals or online animations in their presentation.
Tell the class that transverse waves can travel only through solids whereas longitudinal waves can travel through fluids as well as solids. Then divide the class into groups and ask groups to discuss why transverse and longitudinal waves differ in this way. After groups have developed their own explanations, have a spokesperson for each group present its explanation to the class. The correct explanation can be found at the following URL.
Four common student misconceptions about waves are listed below. Ask students whether each statement is true or false, and have students who correctly identify a statement as false explain why it is false. Continue to keep the misconceptions in mind as you teach lesson content.
- Waves transport matter.
- Waves do not have energy.
- All waves travel the same way.
- All waves require a medium in order to travel.
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 19.1 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
When an earthquake occurs under the ocean, it sends waves through the water as well as the ground. When the energy of the earthquake reaches shore, it forms a huge wave called a tsunami.
- Do you know how large tsunamis are? How might the size of these and other waves be measured?
- What causes some waves to be bigger than others?