Modeling The Conservation of Momentum

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Students will be able to build a model to investigate the conservation of momentum

Big Idea

Total momentum before and after an interaction remains constant within an isolated system.


5 minutes

The goal of this lesson is for students to demonstrate their understanding of the conservation of momentum by creating a visual that illustrates the conservation of momentum using information from notes and a simulation. This lesson relies on the explanations students construct in an earlier lesson on momentum as well as their ability to communicate information about momentum and its conservation visually. This lesson addresses the HS-PS2-2 standard because it asks students to analyze the motion of objects during elastic and inelastic collisions using the idea that the total momentum is conserved when there is no net external force. It aligns with the NGSS Practices of Developing and Using Models (SP2), Planning and Carrying Out Investigations (SP3), Analyzing and Interpreting Data (SP4), Constructing Explanations (SP6), and Obtaining, Evaluating, and Communicating Information (SP8) because students create a visual that demonstrates an understanding of the conservation of momentum.

Within this lesson, students use a laboratory investigation and an interactive activity to craft an understanding of the conservation of momentum. Students work in pairs to create visuals on the conservation of momentum. Finally, students identify an area of strength and an area of growth that highlights their assessment of their understanding of the most important and challenging parts of the lesson. Within this lesson, I ask students to focus on communicating their current understanding of the conservation of momentum. I assess student understanding throughout the lesson using informal check-ins and assess each student's work at the end of the school day on a scale of 1 (Advanced Beginner) to 5 (Highly Proficient).


5 minutes

During this portion of the lesson, students complete a routine where they write the objective and an additional piece of information in their notebooks. I project a slide with the date, the objective and an additional prompt  on the interactive whiteboard with a red label that says "COPY THIS" in the top left-hand corner. Sometimes the additional prompt is a BIG IDEA for the lesson or the Quote of the Day or a Quick Fact from current events that is related to the lesson. The red label helps my students easily interact with the information as soon as they enter the room and avoids losing transition time as students enter the classroom.

Today's additional piece of information is a BIG IDEA which states that the total momentum before and after a collision remains constant in an isolated system.  After students complete the bell ringer activity, I display this simulation on the interactive whiteboard at the front of the room.

After I load the simulation, I ask students to write predictions in the notebooks regarding the velocity of each car after the collision. After 1 minute has elapsed and students are done writing their initial predictions, I start the simulation. I ask students to write whether the outcomes support their predictions or do not support their predictions in their notebooks. If the outcomes does not support their predictions, I ask students to write suggestions as to why their predictions are not supportable. After a minute has passed, I reset the simulation then ask students to write predict what happens if I change the masses of the cars to be unequal. I change the masses of the cars and repeat the demonstration asking students to record whether their new predictions were supported or not.  

I choose this simulation because I wanted students to have a quick way to test their predictions. This simulation helps students revisit concepts like the forces acting on an object and the idea that the total momentum of a system remains constant regardless of the masses and velocities of the objects involved in a collision. I also choose to run this simulation on the interactive whiteboard as a way to have a low-pressure way for students to gather evidence that either supports or does not support their hypotheses. 

Conservation of Momentum Overview

20 minutes

After introducing students to the simulation in the bell-ringer activity, I spend 1-2 minutes distributing Chromebooks and this handout for student pairs to use during this section of the lesson. I ask students to spend the next twenty minutes working in pairs using a simulation to investigate the conservation of momentum of a system for three scenarios:

  • An elastic collision between equal masses
  • An elastic collision between unequal masses
  • An inelastic collision between unequal masses

I do not give students a recipe lab with a set of traditional numerical constraints. Some student pairs follow the handout in tandem, while other student pairs take turns completing a task and a few student pairs split the work up into sections and explain their solution to their partner after each section is complete.

While this may seem chaotic, I encourage student choice because I want students to be fully engaged shareholders who construct explanations of the conservation of momentum using an investigation they create within a set of theoretical constraints. I choose this activity because I want students to learn that momentum is conserved in the absence of an applied force.

Conservation of Momentum Investigation

25 minutes

After students analyze the conservation of momentum using a simulation, I ask them to test the model using a hands-on lab. I choose this activity because I wanted to emphasize the importance of collaboration during scientific investigations. I have students work in groups of four at lab stations using defined student roles of task manager, resource manager, facilitator, and recorder. 

The student with the task manager role reads the procedure aloud and asks me clarifying questions about the required tasks. 

I ask teams to send a resource manager to obtain:

  • 1 car track
  • 1 pair of cars 
  • 1 elastic band
  • 1 tube of clay
  • 1 triple beam balance
  • 1 stopwatch

The student with the facilitator role makes sure that everyone participates in the lab activity and keeps the group working toward completing the tasks by the end of the 20 minute time limit. The recorder copies data for the group in a table in his or her lab notebook that includes the trial number, the type of collision, the mass of each vehicle and the velocity of both cars at different points of the collision. During the last 5 minutes of this section, the recorder then shares the data table with the rest of the team. Each group member then records the team data table into his or her notebook.

Within this section, I want students to determine the momentum of objects both before and after a collision and to identify whether momentum is conserved or not within a system in the absence of an external force. Students spend about 20 minutes completing this activity that asks them to measure the momenta of two cars for both elastic and inelastic collisions. Students refine their designs using information they have gathered during their experiment. During this 20-minute portion of this section, students determine the velocity of each car before and immediately after the collision. Click here to see an example of student work.

Conservation of Momentum Visual

25 minutes

Once students are done organizing their lab notes, I project a Conservation of Momentum Visual Guide on the interactive whiteboard. I create this activity because I want my students to learn that momentum is conserved within a system of objects in motion in the absence of external forces. I distribute bins which contain colored pencils, markers, poster paper and Chrome books to each team. Students work in pairs and spend the next 25 minutes creating a visual that represents their understanding of the Conservation of Momentum.

Each visual must include:

  • Illustrations of elastic collisions
  • Illustrations of inelastic collisions
  • Example problems and solutions using a solutions protocol

Students use information from today's lesson, class notes and our digital textbook to create their visuals. Student can choose to create visuals by hand on poster or chart paper or digitally using Prezi, Powtoon, Popplet, Padlet or Powerpoint.


5 minutes

Once students are done creating their visuals, I ask them to add their names to the visuals and to place them on the resource table or turn them in digitally. I ask students to clear their immediate area before the next class begins.Then, I ask students to write one area of strength and one  area of potential growth in understanding of the important portions of today's lesson.

Some student responses include, " I understand how to use a simulation to show that momentum is conserved," and "I struggle with using clay correctly to help make a collision inelastic". I use the information from student responses to determine possible new pairings that help students move more effectively through material. I also keep track of student self-reporting of their current understanding levels in the notes section of my digital grade book. After five minutes pass and students complete their exit slips, I collect the slips to grade. To wrap up this lesson I ask students to complete the problems and exercises at the end of this chapter for homework.