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# Newton's Second Law and Free Body Diagrams, Part 1

Lesson 3 of 10

## Objective: Students will be able to identify when an object has a net force and its direction. Given the net force, students will be able to solve for acceleration or mass.

*60 minutes*

The goal of this lesson is for students to see how free body diagrams can be used as a tool along with the Newton's second law relationships and equation to solve for acceleration and mass (HS-PS2-1). This is the first time they will determine what the numerical net force is on an object using a free body diagram. Students will use models we have created for free body diagrams and Newton's second law (SP2) to help them to solve problems using computational thinking (SP5) and eventually sharing out their work and explaining it to the class (SP8).

I have students work on the Free Body Diagram and Net Force WS #1. Students work with their table groups to complete the problems because they will be explaining a problem to the class in the whiteboard session later in the lesson. After about 20 minutes, I assign each group a problem for whiteboard presentations. For their whiteboards, I expect students to show the free body diagram they used (if necessary) and all of the work to solve their problem. I walk around with the FBD and Net Force WS #1 KEY to make sure students are on the right track.

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After students have completed the problems on the worksheet and the whiteboard for their assigned problem, I have students prepare for the whiteboard presentations with their table groups of 3-4 students. To do this, they discuss as a group what the best answer is to put on the board and show all of the work on the whiteboard. They also discuss how to explain this problem so that each person in their group understands.

After the students have spent about 5 minutes preparing their whiteboards, they have the worksheets out and focus on the front of the classroom for the presentations. As students present their work, I expect the presenters to have multiple members of their group speak during the presentation and to walk the rest of the class through their problem-solving process. From the audience, I expect students to be checking their answers and asking questions if they don't agree with or don't understand how they presenting group got their answer. If the students in the class do not ask a question, I ask one of the group.

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To end class, I give students the End of Discussion Checkpoint #1 to see what they can do on their own in terms of solving a problem that has them use a free body diagram and Newton's second law. I use this as a formative assessment to let me know where each student is and and to let the students know where they are at with understanding the new material. I use this as a small grade for students and return it to them the next day.

#### Resources

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- LESSON 1: Modified Atwood Machine Lab
- LESSON 2: Determining and Using Newton's Second Law
- LESSON 3: Newton's Second Law and Free Body Diagrams, Part 1
- LESSON 4: Friction Lab, Day 1
- LESSON 5: Friction Lab, Day 2
- LESSON 6: Elevators and Newton's Second Law
- LESSON 7: Newton's Second Law and Free Body Diagrams, Part 2
- LESSON 8: Newton's Second Law with Groups
- LESSON 9: Newton's 2nd Law Review Day
- LESSON 10: Forces and Acceleration Test