Throughout this unit students have become familiar with the concepts of work, mechanical energies, and energy conservation. So, today's goal is to expand students' understanding of energy to include the energy transformation within a spring (HS-PS3-1). After a brief demo, students will watch a video on the concept of elastic potential energy (SP8). To evidence their learning, students will then create concept maps and work through some practice problems (SP5).
The introductory demo requires a mass with a hanging spring.
To give students an opportunity to visualize what today's lesson is all about, I start the lesson off with a demo that shows the energy transformation of a mass-spring system. Before the class enters the room, I have a spring suspended from a ring stand, with a mass on the table next to it, at the front of the room.
Before I show the students anything, I ask them to contribute the definition of gravitational potential energy. I take volunteers to answer the question, and I allow students to contribute until we get the proper definition. After the class has recalled that gravitational potential energy is dependent on mass, height, and gravity, I ask students to contribute what they think spring (aka elastic) potential energy will be dependent upon. I make a list of these contributions on the whiteboard at the front of the room so that we can refer back to them after the demo.
At this point, I call a volunteer forward to hang the mass on the end of the spring. Once she hangs the mass on the spring, the spring obviously stretches downward and should oscillate after the mass is released. As the mass is oscillating, I ask the students to take a second look at our list on the whiteboard and think about which of our contributions accurately describe the potential energy of the system. I give them just a few moments to sit quietly, observe the mass-spring system, and internalize the list.
After approximately 90 seconds of sitting quietly, I ask students which items from our list are evident in the demo. I circle these items (students chose mass, height, and the potential energy equation) and leave the entire list up on the board so students can check if they are right as we move into the next activity.
Because there are so many great resources on the internet and I had an introduction that was teacher-led, I've decided to use this Khan Academy video to present how potential energy is stored in a spring. Before I start the video I make sure my expectations are clear. Students need to be sitting quietly, listening and watching the video, and taking notes on meaningful material. To me, meaningful material includes any reference to previously learned concepts, equations, vocabulary, and examples. I am telling my students these expectations as I'm on my way to start the video.
As we watch the video I pause it in several places to give my students an opportunity to process and internalize this new information. I use a discussion guide to remind me where to stop and what important material or questions I want to share with the students. When I pause the video I'm somewhat flexible in our discussions, meaning if a student has questions or needs further explanation I take the time to do that. I always write down any equations on the front board so that students are sure they have copied them properly.
After the video is over, I give each student a sheet of blank, white, 8.5" x 11" paper and explain the directions for concept mapping. My students have all done concept maps before in this class, so I provide students a simple model on the front board. I want students to put energy at the center of their map, so the students need to fill in as many off-shoots as they feel are necessary. My blank model that I draw on the board looks something like this.
I make sure each student grasps the concept map idea by checking for understanding. I ask "Does everyone get this?" and then pause for about three seconds. If someone has questions I address them, but otherwise we move on. This means it's time for students to work and create their own maps! I keep the learning environment quiet for this activity, otherwise I've found that the students are less authentic about sharing their own thoughts. Students get about five minutes to work on their individual maps before I collect the maps. Collecting these maps allows me to ensure they included the concepts of kinetic energy, gravitational potential energy, elastic potential energy, work, and conservation of energy.
My students often work through the concept map activity at different paces, so the end of class today will not have a group closure session. Instead, as students turn in their completed maps, they pick up a copy of the spring homework. The goal of this homework is to offer a summative assessment on students' understanding of energy transformations involving springs. It is to be completed by each individual student on a separate sheet of paper. I collect the assignment at the next class period and grade it for accuracy.
As students finish the concept map activity, they may begin to work collaboratively on the homework. I walk around during this work time so that I can answer any questions and ensure that students are on task. My expectation, set at the start of the year so that students are aware of it, is that students productively work until the bell rings.