The Physics of Work

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Students will explore the concept of work by taking notes and solving practice problems.

Big Idea

Today, students learn what it really means to "work" in physics.


As our first lesson of this Work & Energy unit, today's goal is to take students' definitions of work and expand them to include the idea that work, in physics, requires applying a force over a distance. Defining work will allow us to then study kinetic and potential energies before exploring energy conservation (HS-PS3-1). Students will participate in a demo of work before engaging in a reading exploration activity (SP8). The lesson closes with students applying their new knowledge with collaborative problem solving (SP5).

Demonstrating Work

10 minutes

At the start of class, students take out their textbooks so they can participate in today's introduction to work. In the event that students don't have a book, I have some extras available at the front of the room. 

Splitting the class down the middle, I ask students on the right side of the room to hold the book steady out in front of them and parallel to the floor. I have the other half of the students bicep curl their books continuously. Students maintain their task for a full five minutes, and they can see the progression of time on a timer that I placed at the front of the room. As students are participating, I walk around the room and playfully ask how they are feeling.

After the time has expired, students sit down and we debrief about the demonstration. I use a discussion guide to remind me of certain questions I want to ask. My goal is to have students apply what they already know about forces and begin to think about work. For example, students on both sides of the room agreed that they were doing work. When I probed them about WHY they thought they were doing work, students commonly contributed that work requires concentration and effort. 

Since I'm using this demonstration to introduce the concept of work, I then tell students that their ideas of concentration and effort don't apply to the quantity of work in physics. Instead, I ask the students to use physics terms to describe what they were doing with the book. This eventually leads me to describe how the physics definition of work must require both an applied force and a non-perpendicular displacement. So, the arm curling students did work while the stationary book holders did not do work. Throughout our conversation, I've written notes (in purple) on the discussion guide. I record these notes so I can refer back to them throughout the unit and address any topics that are left ambiguous.


Work Exploration Activity

30 minutes

I now allow students to choose a partner and take a computer from the cart at the front of the room. We use MacBook Pro's in my district and each department has a cart that can be shared. At this point in the year my students are familiar with the organization of the computers and cart. I decide to let students choose their partner since I want them to be comfortable and focus on internalizing today's material.

As the computers are booting and after students have pushed their desks together with their partner, I give each student a copy of the work exploration activity. This document is a guideline that helps students identify the absolute minimum material they should record into their physics notebooks. Once they've opened the document, the students follow the link to the Work Section of the Physics Classroom. At this website and still in their pairs, students read through the text and use the document to guide them through the goals of understanding. I let students know that they can read aloud or individually, but the point of them being in pairs is to discuss and determine the most important parts of the text.  

While students are working, I walk around with the answer key to ensure they are actively engaged in the learning process. To me, this means that they are on the proper website, reading or discussing some component of work, and writing down a thorough set of notes. When I walk around, I spot check their written work and engage students in questions such as "So how does work use force?" or "Is work dependent upon distance or displacement and why?" I also use this time to build rapport with students and attempt to make the material meaningful to the individual. For example, if I know a student is currently in soccer season, I might ask him or her "Are there any points during a game when you aren't doing work, but are still in contact with the ball?"

Collaborative Problem Solving about Work

10 minutes

As closure and an informal assessment, students have the rest of the class to start tonight's homework. Students remain with their partners from the paired reading activity as I pass out a copy of the homework to each student. This is an assignment that needs to be completed by each individual on a separate sheet of paper, although they may use their partner from the previous activity as a resource while working in class. I encourage collaboration, as students apply their new knowledge for the first time. 

Also, I walk around to offer help or problem solve with the students as they are working. You might hear me say "Well, which angle is the object being pushed and which direction is it moving?" in response to a student asking about the angle. 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.  

I call the homework informal because I don't want students to get nervous that it will count as a quiz or test grade. Since my goal is to assess their level of understanding, I will collect and grade the assignment for accuracy at the start of the next class meeting. Not only do I want to give students personalized feedback on this homework assignment, as shown in this example, I also want to check the pacing of the course and make sure my students are ready to move on to the next lesson.

This is our closure activity for today and it's meant to have students apply their newly learned knowledge from the paired reading activity. I am also trying to take a step towards a flipped classroom. I like students to have me as a resource when they work through problems, and I think it helps them build confidence. In the past I've attempted to do entire class periods of a full flipped classroom, but it's hard to hold the students accountable for digesting the needed material. I find that a combination of work time (that lasts right up until the bell rings) and in-class learning best fits the needs of my students.