Free Body Diagrams

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Objective

Students will demonstrate and understanding of forces by building quantitative models of the forces acting on an object using the information they obtain from a set of video notes.

Big Idea

Free body diagrams model all of the forces acting on an object.

Overview

The goal of this lesson is to help students use a set of video notes to develop a quantitative model for the forces acting on an object. This lesson addresses the HSA-REI.A.1 and HS-PS2-1 standards because it asks students to solve for the value and direction of each force acting on an object in a step-by-step manner. It aligns with the NGSS Practices of Developing and Using Models (SP2), Using Mathematical Reasoning (SP5) and Constructing Explanations (SP6) for Science because students will use mathematical logic to create quick summaries to explain factors that are related to forces acting on an object. This lesson also is aligned to the NGSS Cross-Cutting Idea of Patterns because students must recognize that the direction of each force corresponds to the conceptual model of that force. 

Within this lesson, students will begin constructing an explanation of the different forces acting on an object using a set of video notes with pause points embedded as green question marks. Students will then use their understanding of the quantitative models from the beginning of the lesson to complete a practice worksheet. Finally, students work in teams to create a visual that connects to the content of today's lesson. Within this lesson, I ask students to focus on stretching their prior knowledge of vectors to address the free body diagram as a model for the forces acting on a body. I assess student understanding throughout the lesson using informal check-ins and assess each student's work at the end of the school day. 

Bell-ringer

10 minutes

This part of the lesson begins with this routine. The objective of the Bell-Ringer is to give students a clear understanding of the focus of today's lesson. 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 piece of additional piece of information is a Big Idea which states that free body diagrams model all of the forces acting on 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. In this lesson, I want students to get ready to leverage information gathered from their understanding of free body diagrams and vectors to construct mathematical models for the total number of forces acting on an object.

EDpuzzle: Balanced and Unbalanced Forces

25 minutes

Within this lesson, I discuss free body diagrams as a way to model the forces on an object. I include a set of notes that I project at the interactive whiteboard in the front of the room. This part of the lesson focuses on identifying whether the forces acting on an object are balanced or unbalanced. For the first ten minutes, I play the notes at the front of the room for the entire class and pause at the pause points I embed as green question marks in the video.

 

During the first ten minutes, students take notes in their notebooks. Once the video is done, I ask students if they have any questions or concerns about the methods discussed in the video. We have a whole class discussion for 2-4 minutes. Some student queries include: "Is there a way to draw the forces going toward the center of the object instead of away from it?" and "What happens if I choose up to be negative, does this change the free body diagram?"  During the last minute of this section of the lesson, I email this video and notes to the entire class so that students can watch, pause and replay the video outside of class. During the next section, students work in pairs to complete a task that relates to these notes.

Infographic: Free Body Diagrams

30 minutes

During this section, I ask students to spend thirty minutes working in pairs to create an infographic on free body diagrams. An infographic is a visualization tool that combines non-linguistic models of information in an eye-catching format that both informs and illustrates a conceptual understanding of a complex topic. I tell students that each infographic must:

  • Include a title that demonstrates the purpose of the visual. 
  • Have a clear and consistent organization that is both engaging and easy to read.
  • Include sources that are credible using the MLA format.
  • Illustrates how to create a Free Body Diagram for 3 distinct scenarios
  • Defines between five and seven types of forces that can act on an object
  • Generates an annotated quantitative free body diagram and corresponding example

I use this type of activity so that students can synthesize the information they gather from the EDpuzzles, class notes and readings from this unit and communicate this information in an accurate and concise manner. I choose to conduct this portion of the lesson as a pair driven activity to keep students accountable for completing the activity at the end of the 30-minute timeframe. In my classroom, students share authority over their learning process and often have a set of choices on how I assess their work. So when a few students ask if creating infographics by hand, I agree. Click here to see another example infographic on free body diagrams.

Students use Chromebooks to research additional information on their topics and find graphics resources from websites like Pixabay and flickr to help communicate their ideas. Most students complete this activity within the given timeframe. However, I give students who are not able to complete this assignment during class the chance to turn it in at the end of the school day. This typically means students work through the advisory period, which is similar to homeroom, and complete the assignment without penalty. I assess this assignment using the common physics rubric found here on the reasoning and logic and representation domains.

Closure

10 minutes

The closure activity this section asks students to write down ideas about free body diagrams in their notebooks using a Free Write Routine. Student responses include: "Free body diagrams are easy to draw once you figure out the size and direction of each force, normal,", "I still don't know why I can't draw all of my normal forces at 90 degrees from the ground", and "Each force type has a formula, once you figure out how to find each type of force, free body diagrams are easy to make".

This type of closure activity helps students to make their current level of understanding visible. To wrap up this lesson, I ask students to look at the EDpuzzles from this week's lessons that I post on the class Edmodo wall.