Introduction to Forces, Part 1 of 2

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Students will construct explanations of the forces acting on a system using information from multiple sources including non-fictional texts, interactive websites and simulations.

Big Idea

Forces are pushes or pulls acting on the center of mass of an object.


The goal of this lesson is to help students construct explanations about the forces acting on an object. This lesson is the first in a pair of lessons and addresses the W.11-12.8 and HS-PS2-1 standards because it asks students to use free body diagrams to model the net force acting on an object. It aligns with the NGSS Practices of Using Mathematical Reasoning (SP5) and Constructing Explanations (SP6) for Science because students use mathematical logic to create summaries to explain factors that are related to a forces acting on an object. Students begin by using an interactive website to construct free body diagrams that correspond to a set of 12 scenarios. Students use a reading and a graphic organizer to summarize information about forces and free body diagrams. During the closure activity at the end of this lesson, I ask students to discuss the most important and challenging parts of today's lesson on forces and free body diagrams.  

I assess student understanding throughout the lesson using informal check-ins, and will assess each student's work at the end of the school day. I want students to learn to integrate information from various points of this course into a set of diagrams that represent the forces acting on an object. This relates to (SP6) because students have to leverage skills like note taking and recognizing patterns to develop an understanding of how free body diagrams are useful representations of the forces acting on an object.  One goal of this lesson is to help students learn that free body diagrams are useful for analyzing the total force acting on an object.


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 forces are pushes or pulls acting on the center of mass of an object. 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 free body diagrams are useful models for studying the forces acting on an object.

Free Body Diagrams

25 minutes

Most students in my class have learned how to use qualitative free body diagrams in 9th-grade physical science and have a general familiarity with the topic of forces. This activity asks them to spend twenty minutes matching scenarios to outcomes using an interactive on computers as a way to activate their prior knowledge. I distribute Chromebooks and 12 scenarios to teams made up of 4 students. I ask that each student in the team use the interactive to construct at least 3 scenarios. I have chosen this activity because I want students to understand how to use free body diagrams to represent the net force acting on an object. 

While students spend twenty minutes constructing explanations that connect each scenario to a free body diagram and discuss the interactive activity with their table mates, I circulate and address any questions students may have. During the twenty-minute period students spend working with the interactive activity, students first click the activity link I post on our Edmodo wall, then choose a scenario, then select a force and its direction. Students click a force arrow in the diagram to change the size of the force it represents and continue to add forces to their free body diagrams until they think the diagrams represent the scenario.

Once student teams agree that the diagram is complete, students click the check button and the interactive gives them feedback on their diagrams. If the diagram is qualitatively correct, students receive a splash screen with a congratulatory message. If the diagram is incorrect, students receive a splash screen telling them that it is incorrect and whether they have chosen the correct force magnitudes and directions. After twenty minutes pass, I ask students to spend the next five minutes creating a Quick Summary that shows the connection between a scenario of their choice and free body diagrams.

At the end of this section, I ask for volunteers from each lab table to share "noticings" and "wonderings" with the class about the interactive activity. Some student responses include, "Gravity always points downward.", "Objects that move have an unequal set of forces," and "I like that the interactive tells me when I choose the correct forces but have incorrect sizes or directions instead of just saying that my diagram is incorrect". During the next section, students work in teams of 2 to 4 to create a collaborative summary on forces and free body diagrams.

Collaborative Summaries: Forces and Free Body Diagrams

30 minutes

After students discuss the interactive activity, I distribute a reading and ask students to spend fifteen minutes silently reading the handout on forces and force diagrams. After fifteen minutes pass, I ask students to spend a minute or two reading the directions below which I project on the interactive whiteboard at the front of the room. 

The directions for collaborative summaries ask students to:

  • Choose a subtopic or subheading of the material students just read
  • Reread a single section at a time
  • Take notes that summarize the main ideas of that section
  • Be prepared to teach that subtopic to the rest of the class
  • Take notes as another student presents their subtopic to their neighbors

There are four subtopics: 1) Defining Forces 2) Types of Forces 3) Naming Convention of Forces and 4) Free Body Diagrams. The instructions for the collaborative summaries make students think beyond jotting down ideas and get them to ponder the importance, usefulness, and multifaceted quality of their informationStudents work in teams of two or four during the Collaborative Summary portion of this lesson. Each student spends 1-2 minutes summarizing a single subtopic. Then students take turns reading their summaries aloud to their group members. While a student is reading their summary aloud their group members write summaries on that student's subtopic on their sheet. Students repeat this process until their summary sheets are complete. Once students are done collecting information we transition into teaching their summaries to their peers who are at the adjacent table. I remind students that science Performance-Based Assessment Tasks (PBATs) involve a teaching component and I ask students to think back to when they were in 9th grade and had to assess science PBAT students based on the oral defense. 

This semester, the PBAT choices include roller coaster safety or car collisions and includes an essential question of "How do forces cause changes in motion?" Students can use their understanding of forces and their peer teaching experiences to demonstrate their understanding of concepts from this semester during their PBAT on physics. Hearing the perspectives of peers can stretch a student's understanding of science through a series of questions and revisions.

Students create the questions and make revisions throughout this portion of the lesson. For example, a student may ask a presenter to explain what is meant by a particular term or "Is that always true?" or "Does that relate to _______?" to get a better understanding of a subtopic from another student's perspective. I collect and grade the collaborative summary sheets and provide feedback at the end of the week. 



10 minutes

This closure asks students to identify and describe their personal level of understanding of key ideas within the lesson. The writing prompt asks students, "If you were to write a headline for this topic or issue right now that captured the most important aspect that should be remembered, what would that headline be?" Students write their responses either in their notebooks on or our Edmodo wall. I like this activity because students identify and share the portions of the lesson they feel are important and challenging as headlines. Student responses include: "Learning how to create a simpler diagram of what is going on in a system", "Forces are pushes or pulls on an object by another object" and "Normal is math for perpendicular to a surface."

To wrap up this section of the lesson, I ask students to look at this tutorial and practice questions that I post on the class Edmodo wall for homework. I check student responses to this closure to determine whether students are proficient in the understanding of the connection between scenario descriptions and the net forces acting on an object at the beginning of the next lesson.