As our first lesson of this Sound Waves unit, today's goal is to take students' knowledge of sound and expand it. Specifically, students learn how the speed of sound changes within different mediums, how sound waves are produced, and how timbre and pitch are related. This lesson on sound allows students to show what they already know about waves (HS-PS4-1 & HS-PS4-5). After students have refreshed their thinking, we take notes on the specifics of sound (as mentioned above). The lesson closes with students applying their new knowledge with some collaborative problem solving and hands-on exploration activities (SP5 & SP8).
The exploration activity at the end of class requires the following materials for each lab group: 2 -3 tuning forks & a Vernier microphone.
Today's class starts off with students recalling what they already know about waves and simple harmonic motion. I have the word "waves" written on the front board and have students pick up a blank piece of paper as they enter the room. Once the bell has rung, I ask students to write down anything and everything they know about waves. They should be working on this individually, as I'm using it as way to assess any prior knowledge. This teaching strategy is also meant to help the students shift their thinking from waves in a string and transverse waves to sound waves.
Once a full 5 minutes has passed, I choose a student to share an idea from his paper. I usually pick the student closest to me, and after he's shared I write his idea down on that front board. We then go around the room and students continue to share, but once a contribution has been recorded it cannot be repeated. This process continues until all ideas have been shared. I leave our example on the board in the hopes that we'll refer back to it throughout today's class.
While students are sharing their ideas, I am internalizing the information they are contributing. Looking at how much, or how little, they know helps me to adjust my pacing and depth for today's class and the entire unit. I'm also trying to identify any misconceptions that were shared so that I can be sure to address and correct those throughout the unit.
It's time for students to take out a sheet of paper and get ready to learn about the characteristics of sound waves. My students are operating under the expectation that they must write down key points from the presentation. This expectation of how to take notes has been outlined and ingrained in their learning since freshman year.
I display the Intro to Sound PowerPoint (also available as a PDF) to help the students understand what they need to write down. As I'm showing the slides on the front board, I have a hard copy of the PowerPoint which includes teacher notes (viewable when the file is downloaded). These notes help me to stay focused and ensure I mention the highlights as we progress through each slide.
The presentation starts with a discussion of how sound waves are produced and relate the compressions and rarefactions of sound waves to a sinusoidal curve. Then, students learn how sound can exist outside our threshold of hearing and how the speed of sound varies as density of the medium carrying the sound changes. After a few examples of applying the speed of sound equation, students define beats, timbre, and pitch.
While I describe this section as "direct instruction," I usually have a lot of interaction with my students throughout the presentation and am constantly moving throughout the room to change my proximity. The students ask questions, participate in problem-solving, and connect to real-world examples to stay engaged the entire time. For each of the example problems that are included in the presentation (key is viewable when the file is downloaded), students are encouraged to collaborate with those students seated around them. I'm also walking around to answer questions and provide assistance when needed. While I don't collect or grade the work to these examples, students know the importance of working through them and understanding the solutions. Homework problems and the unit test will contain similar problems, so at this point in the course students usually embrace the ability to have guided practice time.
As closure and an informal assessment, students have the rest of the class to start tonight's homework. Students remain in their seats, at their lab tables, and are able to work with those people seated around them. This is an assignment that needs to be completed by each individual on a separate sheet of paper. I encourage collaboration, as students apply their new knowledge for the first time.
The homework assignment comes from our textbook, and these problems are similar in difficulty and question type that students are expected to answer on the AP Physics 1 exam. Each question asks students to relate air temperature to the speed of sound. For example, the first question asks students to find the temperature of the air, given the wavelength and frequency of a sound. The fourth question is a bit more difficult: students are asked to find the depth of a well, given time and air temperature.
I walk around to offer help or problem solve with students as they are working. You might hear me say "Well, what do we know about the time given for an echo?" in response to a student asking about question six. My style is to lead the students to the answer, not just provide it for them. That being said, if a student is continually struggling and in obvious need of being shown the answer, I accommodate him or her.
This is our closure activity for today and it's meant to have students apply their newly learned knowledge from the PowerPoint notes. However, as students have been working I also pass around a few sets of tuning forks and microphone sensors. I want students to be able to visualize what we talked about today, so the equipment gives students an opportunity to tangibly explore sound waves. Students are welcome to place the tuning forks on different surfaces, strike the forks with different forces, and view the sinusoidal graphs produced with the microphone sensors. After students are finished exploring, they simply pass the equipment on to the next lab table so that everyone has an opportunity to experience sound waves first-hand.