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# Standing Waves

Lesson 4 of 6

## Objective: Students will be able to define and create standing waves.

*45 minutes*

In the previous lesson, students measured the speed of sound with standing waves in air columns. Today, the goal of the lesson is to expand students' understanding of standing waves to include the standing wave definitions and equations (HS-PS4-1 & SP5). The lesson starts when students actively take notes, which they then apply while using a simulation to create standing waves (SP2 & SP4). Class ends with an analogy prompt closure activity.

#### Resources

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#### Standing Waves PowerPoint

*20 min*

It's time for students to take out a sheet of paper and get ready to learn about the characteristics of standing waves. My students are operating under the expectation that they must write down key concepts from the presentation. This expectation of how to take notes has been outlined and ingrained in their learning since freshman year.

I display the Standing Waves 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 and sample problem solutions (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 defining standing waves and showing students a video of a standing wave on a string. Then, students contrast nodes and antinodes before looking at the equation for a standing wave on a string. To relate the notes to yesterday's lab, the presentation defines resonance and offers students two videos that demonstrate forced vibrations. Finally, students try to solve two sample problems that allow them to apply their newly learned knowledge. I solve these problems prior to the start of class so I can share the solution with the students. Having the solution written down ahead of time allows me to show my written work to the students under the document camera while answering questions students have about the solution.

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, 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.

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#### Standing Waves Simulation

*20 min*

Now that I've properly defined standing waves, students use a computer simulation that allows them to be more active in their learning. The simulation allows students to visualize and create a standing wave using a virtual wave on a string. Students are also able to analyze one pulse at a time and analyze the type of interference that occurs. The simulation also gives students an opportunity to alternate between fixed-ends and free-ends and contrast the interference patterns that result.

Before we start the activity, I assign partners using the random student generator that already has my students' names loaded. By displaying the random generator on the front board, there is an element of suspense as the partners are assigned. Partners work best for this activity so that each student can be actively engaged throughout the work time. Because this activity does not need to be completed outside of class, I feel comfortable in choosing the pairings for my students.

We use MacBook Pro's in my district, so my students are familiar with how the computer and cart organization works. After each pair has been assigned, the students move to sit near each other, push their desks together, and grab a computer. As the computers are booting I pass out the standing waves simulation so that each student receives a copy. This document directs them to PhET where they will be using waves on a string simulation. My activity sheet is also meant to direct the students in their learning so that they are confident in what material needs to be understood.

While students are working, I walk around to ensure they are actively engaged in the learning process. This means that they are on the proper website, reading or discussing some component of the simulation, and writing down appropriate information from the simulation. When I walk around, I'm spot checking their written work and engaging students in questions such as "Have you changed the end of the wave to a loose end yet?" or "Why do you think it's important to have the tension set so high?"

When there is approximately 10 minutes prior to the end of class (5 minutes left of the time I've allowed for this activity), I ask students to put the computers back on the cart and return to their seats. I also tell them at this point that the lab is due at the start of the next class meeting. Once everyone is back in their seats, we are ready to move into the closure activity for our lesson.

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With about five minutes left of class, I ask the students to stop working and focus on me for a moment. I remind students that the purposes of today's activities were to define and explore standing waves. As I'm talking, I give each student a small, blank notecard.

Once everyone has a notecard, I ask students to respond to an analogy prompt that is on the front board. I've put the prompt on the board while the students were working, and it's been hidden from their view so they aren't able to think too deeply about their responses. As I reveal the prompt to the students, they must write the prompt and their responses on the index card. For this particular activity, the prompt will say "This standing wave activity was like _________ because _______."

This is their "ticket out the door," meaning that they can't leave until they've handed me their card. To avoid anyone sneaking out of the room, I stand at the door and collect the cards as students depart. Once I've collected all of the cards, I read and use them to adjust my teaching practices. For example, if a student says "This standing wave activity was like a marathon because it was way too long." I might take a question off the activity before doing it again the following year. It's always fun to read some of their creative contributions.

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