Selecting big ideas/models
Brian’s 9th grade physical science textbook includes a long unit of instruction about waves and energy presented through multiple chapters of text. The chapter about waves covers many different kinds of waves and includes formulas for calculating wave properties such as frequency. The chapter about sound covers everything from sound intensity to echolocation to the Doppler Effect. An overwhelming number of topics are addressed in paragraph after paragraph of expository text with few opportunities for students to examine science ideas for themselves.
Topic focus |
Process focus |
Theory focus |
Instead of following the textbook page by page, Brian decided to focus on helping students understand how mechanical energy can transfer from something like a vibrating guitar string, drum head, or tuning fork into compressional waves of sound energy traveling through air. He also wanted to help students understand how two qualities of the sounds that we hear – pitch and volume – are caused by properties of frequency and amplitude in waves. Once students have made sense of these central ideas about waves, energy, and sound, Brian plans to investigate other sound events like echoes, sound-proof rooms, and the Doppler Effect. By taking a theory focus, rather than a topic focus (see the continuum above), for this unit of instruction, Brian hoped that students would construct theories of sound and waves that could be used to understand many different events in their lives.
Brian used a number of models to help students understand and explain sound events. First, students 
constructed their own models about how musical instruments and tuning forks create sounds that can travel through the air to listeners. Second, Brian introduced representations of sound waves as compressions in a Slinky toy and as compressions in air particles to help students think about how unobservable processes, like energy transferring through collisions between air particles, are responsible for the observable qualities of sound that we hear when musical instruments are playing or when a tuning fork is ringing.
Finally, students synthesized their own representations of sound with representations that they picked up throughout the unit in order to generate final models and explanations for differences heard in the pitch and volumes of various instruments at a concert venue.
