Work - Kinetic Energy Theorem

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Students will qualitatively and quantitatively define the work-energy theorem.

Big Idea

Students explore the relationship between Work and Kinetic Energy.


In the previous lesson, students were introduced to the concept of work. After I refresh students' memories with a ranking task, students take notes on the work-energy theorem. Today's goal is to connect work with kinetic energy (HS-PS3-3), so class will end with students applying their new knowledge to a practice AP Physics 1 problem (SP5).

Introduction with a Ranking Activity

10 minutes

When students walk into class, today's ranking task is already projected onto the screen at the front of the room. I choose this task because it asks students to apply their knowledge of work, specifically how work is proportional to force times distance, which is something we covered in our last class hour. The task should be a slight challenge, but this introduction is meant to get students thinking about work.

Once the students are settled, I read the instructions from the top of the activity. My reading of the instructions is to ensure students understand that class has started. I emphasize to students that they should work individually and take about 5 minutes to rank the graphs, explain their reasoning, and then assess their level of confidence. During these 5 minutes of work time, I walk around the room and informally assess how students are doing with simple glances at their work. My changes in location help students stay quiet and focused.  

When the 5 minutes are over, I reveal the answers to the students by writing them onto the front screen: C, F, E, D, B, A. I then ask if anyone got all of the answers in the correct order. This student has the right solution and is willing to share with the rest of the class. He starts by highlighting the fact that each boxcar must stop in the same distance, so work becomes proportional to only force. Then, he explains that since force equals mass times acceleration, the mass and change in velocity are what will determine the force required to stop each car. After he completes his explanation and shows a few of his calculations to support the numbers written on his paper, I end the introductory activity by asking if anyone requires further clarification. Because this activity reviews material from the previous class that we apply in today's lesson, the students keep their work to use as a reference.

W-KE PowerPoint

25 minutes

It's time for students to take out a sheet of paper and get ready to learn about the work-kinetic energy theorem. 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 Work-Energy PowerPoint 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 the definition of kinetic energy and as I'm going through the slide I ensure my students understand the units for each variable in the kinetic energy equation. Then, students are asked to apply the kinetic energy in a sample problem and share their answers with the rest of the class. After giving students about two minutes to work on the example, I share the solution before moving on to discuss how work and kinetic energy are related. Finally, students work through three more sample problems (in the same manner as described above).

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.

Closure with an AP Practice Problem

15 minutes

Because students are already familiar with my suggestions for solving AP Physics 1 free response questions, I simply tell students to put everything away except for their calculators and equation sheets. Once everyone is situated and quiet, I give each student a copy of an AP practice problem that applies the W-KE theorem. It's my goal to simulate the environment of the AP Physics 1 test, so students are limited in time and must have the problem completed at the end of class time. I maintain absolute silence throughout their work time, and walk throughout the classroom to ensure students aren't cheating.

At the end of the hour, when the bell rings, students come forward and show me their work. I'm standing at the door, so I quickly scan each student's work before handing them a copy of the rubric. I purposely choose this AP problem so students can apply their newly-learned knowledge. Providing students with the rubric as they leave the room allows them an opportunity for immediate feedback. My students understand that they need to take the rubric, compare it to their solution, and score their work appropriately.

Scoring their own offer students insight into how well they've grasped the material. It also shows students what AP Physics 1 readers are looking for in a strong answer and gets students thinking about how they might score on the AP exam at the end of the year. Not only is self assessment a powerful learning opportunity for the students, but it also takes some of the burden off of the teacher. Students turn in their scored problems at the start of the next class period and I record their grade.