# Practice Problems: Impulse

## Objective

Students will use the G.I.R.L.S. Protocol to solve problems related to the impulse of an object.

#### Big Idea

Impulse is linearly related to both force and time in a system.

## Overview

The goal of this lesson is to help students use the G.I.R.L.S. (Givens, Image, Relationship, Looking For, Solution) protocol to solve problems that relate to an object's impulse. This lesson addresses the HS-PS2-2, HSA-SSE.B.3 and HSA-REI.A.1 standards because it asks students to use a triangular model of the impulse of an object to solve a linear equation for either impulse, force or time, and asks students to look at the momentum changes in a system with non-zero net force. It aligns with the NGSS Practices of Using Mathematical and Computational Reasoning (SP5) and Constructing Explanations for Science (SP6) because students use the G.I.R.L.S. protocol to solve a set of practice problems and take notes from a set of slides to explain factors that are related to an object's impulse. This lesson uses a protocol that students use earlier in this unit to solve problems that relate to momentum.

Within this lesson, students use a triangular model of an object's impulse to determine the impulse, force and time of an event within a system in the context of a word problem. Students then work in pairs to use their understanding of impulse to complete a set of practice problems. Finally, students complete a set of physics quick checks on impulse. Within this lesson, I ask students to focus on deepening their current understanding of impulse. 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).

## Bell-ringer

10 minutes

This portion of the lesson begins with a routine where students write the objective and additional piece of information in their notebooks as soon as they enter the classroom. 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 impulse is linearly related to both force and time. The objective of the bell-ringer is to give students a clear understanding of the focus of today's lesson.  I want students to learn that using a solution protocol can be helpful in solving real world problems that relate to the change in momentum of an object.

## Using a Triangular Representation of the Impulse Equation

15 minutes

During this section, I project a set of Notes on the interactive whiteboard at the front of the room which asks students to "Use the triangular model of the impulse equation to solve for each of the three terms: Impulse, Net Force and Time" as a focus statement. I ask students to write the notes in their notebooks and create two additional equations for Net Force and Time using the triangle equation model with their table mates. Then I ask a volunteer to show how to generate the three equations. I then take a temperature reading to see whether students agree with the volunteer student's solution.

This activity asks them to use routines from earlier in the semester to understand physics content later in the lesson. After five minutes elapse, I ask for three new volunteers to write the three forms of this equation and to identify the situations where each form of the equation is most useful on the interactive whiteboard at the front of the room. I want students to understand how important identifying information from mathematics is to understanding patterns within physics content.

The goal of this section of the lesson is to use both guided notes and group discussion as ways to make connections between the triangular model and the mathematical model for impulse. At the end of this section I ask for volunteers from each station to provide a verbal summary of where they are because I want students to give me a feedback and to provide candid reflections on the ease of the task and the connections between the information they collected and concepts they already know. Students discuss how easy or difficult it is to solve for impulse, force or time and note the conditions when each formula is most useful. This helps me see where they are in terms of their ability to apply mathematical logic to physics concepts. During the next section, students are given a chance to apply these skills to using the G.I.R.L.S. protocol to solve problems about impulse.

## Pair Work: Impulse Problems

45 minutes

After students discuss the triangular representation of impulse, I project an Impulse Example Problem on the interactive whiteboard and show students a step-by-step solution of a word problem on comparing the impulse of two objects. I also post these word problems on our class Edmodo page and distribute Chromebooks for students to use in pairs. Then I ask students to work in pairs to spend about 15 minutes solving the problems found here by writing solutions in their notebooks or on whiteboards from the resource area in the front of the room. Click here for an example of student work. After students solve the practice problems I have three volunteers share their solutions on the white boards at the front and side of the room.

After we discuss the practice problems, I ask students to work together on this handout. I post the link to this handout on our class Edmodo page. This handout includes information on both impulse and momentum and requires students to use information from class notes and this website to complete.

I use this type of activity so that students can process the information at their own pace. I choose to conduct this portion of the lesson as a pair-driven activity to keep students accountable for completing the lesson at the end of the 30-minute time frame.

## Closure

10 minutes

The closure activity asks students to spend about ten minutes solving real-world problems similar to those we introduce in the lesson. This activity works to make student thinking visible regarding the mathematical reasoning behind a solution to physics problems. Students write responses to this activity on the sheets I provide. I check student responses to this closure to determine whether students are proficient in the understanding the mathematical behavior of key impulse terms.

The class average on this quick check is a 4.1 out of 5. Most students choose the second problem as their assessment. To wrap up this lesson, I ask students to read sections 8-3 and 8-4 in our digital textbook on impulse and momentum.