Defining Impulse

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Objective

Students will be able to quantitatively and qualitatively define impulse as it relates to momentum, force, and time.

Big Idea

How does momentum relate to impulse? Today, students define impulse and use what they already know about momentum.

Context

In the previous lesson, students were introduced to linear momentum. After I assess students prior knowledge with a ranking task introduction (SP5), students take notes on impulse. Today's goal is to connect our knowledge of momentum with impulse (HS-PS2-2), so class ends with students creating concept maps

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 specific task because it asks students to apply their knowledge of momentum, which is something we covered in our last class hour. The task should be a challenge because students have not yet been taught that the change in momentum is equivalent to impulse.

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 stopping time of each car, 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:  G=H, F, C=D, B=E, A. I then ask if anyone got all of the answers in the correct order. This student had the right solution and was willing to share with the rest of the class. After he completed his explanation, which was of proper depth, I ended the introductory activity by asking if anyone was in need of further clarification. Because this activity was meant to review material from the previous class and we'll apply that knowledge in today's lesson, the students keep their work to use as a reference.

Impulse Notes

20 minutes

It's time for students to take out a sheet of paper and get ready to define impulse. 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 Impulse 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 notes start with an explanation of changing momentum and then ask students to differentiate between the magnitude of a momentum change and the change in momentum. Students then learn how the change of momentum, force, and time are all linked together and impulse is defined. After students are introduced to impulse in terms of the area under a force v. time graph, they then work through a final example problem that asks them to quantitatively use momentum and impulse. Each time students work through a sample problem, whether it is conceptual or computational, I give students several minutes to re-read the question, think about the question, and then attempt to solve it. Students may quietly collaborate with those seated around them during this time, and then I share the solution and explanation.

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 will ask questions, participate in problem-solving, and connect to real-world examples to stay engaged the entire time. 

Concept Map Closure

20 minutes

After we finish taking notes on impulse, 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 the word "momentum" at the center of their maps, 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 the rest of the class to work on their individual maps before I collect them. Collecting these maps allows me to ensure they included the concepts of mass, velocity, change in momentum, and impulse around the word momentum. The goal of of this concept map is to ensure that students are able to link the concept of momentum from yesterday's class into today's lesson on impulse.