Exploring Elastic Energy

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Objective

Students will be able to conceptualize elastic potential energy and its connection to Hooke's Law.

Big Idea

Students explore the concepts of elastic potential energy and restoring force when they use a masses and springs simulation.

Context

Students have already been introduced to the energy transformations within springs during the work and energy unit, so today's lesson kicks off the simple harmonic motion unit with a spring review (HS-PS2-1 & HS-PS3-1). Students start by showing what they know about springs, before they use a simulation to visualize the concept of elastic potential energy (SP2 & SP4). To bring today's lesson full circle, students watch a short video on how springs are engineered.

Show What You Know: Springs

10 minutes

Today's class starts off with students recalling what they already know about Hooke's Law & elastic potential energy. I have the word "springs" 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 springs. 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 rotational motion into springs and simple harmonic motion.

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.

Spring Simulation Activity

35 minutes

After we've finished recalling the concepts of springs, students use a computer simulation that allows them to be more active in their learning. The simulation allows students to hang masses on springs and explore energy transformations as tension and damping are adjusted. Specifically, students start by calculating the spring constant in the first hanging spring. Then, students graph the displacement of the spring from equilibrium versus the mass. The point of graphing is to identify a k value, compare that value to the calculated value, and then predict masses. Finally, students use the simulation to analyze energy transformations before moving the entire system to another planet and calculating that planet's acceleration due to gravity.

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 spring simulation activity so that each student receives a copy. This document directs them to PhET where they will be using the masses and springs 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. The answers to the questions and graphs may be completed on the activity handout, on a separate sheet of paper, or typed on the computer.

While students are working, I walk around to ensure that students 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 brought the system to a new planet yet?" or "In your own words, what does damping mean?" 

The students' written answers are the most important part of this activity, so I ensure they are thinking through how they provide evidence to any claims they make. I do a lot of walking and questioning throughout their work time to ensure they can justify anything that has been written down. The AP Physics 1 exam places a lot of emphasis on justifying thought processes, so my goal in our dialogue is to practice with students how to successfully justify their arguments.

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.

Engineering Springs Video Closure

5 minutes

After students have finished with the elastic potential energy activity, I hope to pique my students' interest in springs by showing them a video of the manufacturing process. Many of my students want to go pursue engineering, so the video is an attempt to show them how engineers use physics to design springs.

I don't normally like to end a class with a passive activity for students, but they were so active throughout the lesson today that it seems like a fitting activity to formally end class. The video runs exactly five minutes long, so there usually isn't much opportunity, if any, for discussion after it's over.