Reviewing Linear Momentum

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Students will be able to solve and explain linear momentum problems.

Big Idea

Students take on the role of teacher today when they share their solutions to linear momentum practice problems.


This lesson is meant to serve as a final review before students take a unit exam on linear momentum. The lesson starts with an AP practice problem (SP5), before students solve problems involving impulse and conservation of momentum (HS-PS2-2). Students need this final opportunity to review, so this process of problem solving, explaining, and sharing helps students practice and apply their linear momentum knowledge. Specifically, after students are done working through an AP practice problem, they get into small groups to collaboratively solve one linear momentum quantitative problem. Once they are done solving, students come to the front of the room and share their solutions with the rest of the class.

Introduction with a Linear Momentum AP Problem

20 minutes

Because the AP Physics 1 exam has five free response questions that students must work through in ninety minutes, this practice problem serves as a warm-up activity for today's review. I choose this specific problem because it forces students to use principles of momentum conservation and energy in collisions. When students enter the room I hand each student a copy of the problem. My classroom has a routine, so students know that when they are handed a practice AP problem, they must pull out their equation sheets, calculators, and pencils. 

The warm-up officially starts when I remind students of several free response suggestions. Then, students work individually through the practice problem as I walk around to informally assess how much progress they are making through the problem. Students get precisely fifteen minutes to work on the problem, since that's about the amount of time they are given in the actual AP exam.

Once time has expired, I share with the students the grading rubric by displaying it on the front board with a document camera. I go through and explain how the points are distributed while students check their own work against the solution. The students can ask general questions during this time, but I encourage them to see me after class if they have a specific question about their own work. This entire process takes about five minutes, and I encourage students to be as honest as possible in their self grading, since one goal of this activity is to see how well they'd do if this question were actually on the AP Physics 1 exam.

Students Collaboratively Solve Linear Momentum Problems

10 minutes

Today's class uses collaborative problem solving as a way for students to review linear momentum. Students are each given a different problem from a review problem set. These problems are taken from our textbook, and are problems that I feel are most representative of the test questions. Students stay at their lab tables for this activity so we don't lose time while they get into groups

I give each group one of the problems with its final answer. Including the final answer with the problem is an important part of this activity. I want students to not focus so much on getting the right answer, but on being able to explain their reasoning and justify their decisions. The problem that each group receives is random: I literally walk down the center aisle and give the group whichever problem is on the top stack of my pile. All of the students should be able to answer any of these questions.

My expectation is that students take about ten minutes and actively work together to write down the solution on their papers. Without giving the students too many details, I tell them to be prepared to not only show their solutions, but to also be able to explain their solutions. Also, I encourage students to use pen as they work. Using pen keeps them from erasing, so even if they make a mistake or change their thinking, I can see evidence of their entire thought and solution process.  

As students are working at their lab tables, I walk around and ensure that everyone is engaged in the discussion and thinking critically about their assigned problem. I am willing to give students hints as I observe, but my feeling is that by this point in the Linear Momentum Unit students should be able to independently work through these problems.

Students Share Linear Momentum Solutions

20 minutes

After the collaborative work time is over, I share with students that they are presenting their solutions to the rest of the class. Each group comes forward, puts their problem with the solution under the document camera, and explains that solution to the rest of the class. The goal of this activity is to show students the variety of problems that are on the unit exam.  

Because my students are sometimes shy, I ask if any groups volunteer to go first. There is always at least one group that wants to get the presentation out of the way, so I choose them and applaud them for being so willing. This first group of students walk to the front of the room and place the problem with solution under the document camera. One person from the group must read the problem aloud so the entire class becomes familiar with that problem. A second student should explain any diagrams that were drawn and the list of given information. Finally, a third student from the group verbalizes the solution that has been written on the paper. Once the solution is appropriately provided, I ask the class if they have any questions for the group. If someone from the class does need to ask a clarifying question, or if I need to ask a clarifying question throughout the solution sharing, I expect that any presenting group members who haven't participated yet answer these questions.

Once that first group is finished, I let them pick which group they'd like to see share next. This chosen group comes forward with their problem and solution, shares, and appropriately answers questions as the last group did. The process repeats itself until all problems have been shared. This solution sharing activity is our closure to the review lesson today. If students took good notes throughout this activity, they now have a great study resource of new questions with solutions.