Newton's Second Law in 1-D

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Students will be able to identify Newton's Second Law and apply it to 1-dimensional motion.

Big Idea

1-D motion and Newton's Second Law collide today.


At this point in the Newton's Laws Unit, students have already defined force, drawn free body diagrams, and explored Newton's First Law. They've also completed a unit on 1-Dimensional kinematics.  

Today's lesson is meant to introduce students to Newton's Second Law and then provide an opportunity to apply it in 1-D situations (HS-PS2-1). The class starts with a ranking activity to stimulate thinking and then moves into a paired reading activity (SP8). Finally, students get to apply their new knowledge towards the end of class with collaborative problem solving.

Introduction with a Ranking Activity

10 minutes

Because my students indicated in the first lesson of this unit that they were familiar with Newton's Second Law, today's introduction is meant to assess that depth of prior knowledge. Specifically, I choose an activity that will require them to think about acceleration, since it's a key component in Newton's Second Law. When students walk into the room the arrow acceleration ranking task is already projected onto the screen at the front of the room. They are also expected to pick up a copy of the ranking task before they get seated. 

Once the students are settled, I read the instructions from the top of the activity. My reading of the instructions is to ensure students understand that class has started. I emphasize to students that they should work individually and take about five minutes to rank the graphs, explain their reasoning, and then assess their level of confidence. During these five minutes of work time, I walk around the room and informally assess how students are doing with simple glances at their work. My changes in location help students stay quiet and focused.  

When the five minutes are over, I reveal the answers to the students by writing that all accelerations are the same onto the front screen. I then ask if anyone knew and was confident in the idea that each arrow has the same acceleration. Since my students are fabulous, inevitably there is at least one who did and is willing to admit it. It's that student that I then ask to explain his or her reasoning.  If the explanation is complete and clear, I commend the student! In the event the explanation needs to be expanded, I still commend the student, but then contribute any missing information so the whole class has a complete understanding of the material. Regardless, I end the introductory activity by reminding students that even though we are talking about force, we cannot forget what we know about acceleration.

Reading About Newton's Second Law

15 minutes

To learn the fundamentals of Newton's Second Law, students engage in a paired reading activity. I introduce this activity by passing out the paired reading - second law document to each student and explaining that I have already chosen their partners.  Partners work best for this activity, and I already made a list of who will be working together based on their current grade in the class. I don't tell the students how I've paired them, but I ranked the class by overall grade, split the list in half, and then matched the first names on each list. Because there was an odd number of students, I made an exception and had one group of three. Pairing students this way forces them to work with someone different and ensures that ability levels are somewhat equal. To save class time, I printed this list and organized the pairs prior to class starting.

Now that students understand they don't need to scramble for a partner and have the document in front of them, I share how this paired reading activity works. I expect that the students read one page at a time individually while annotating the text with information they deem important. Students should stop reading when they get to the end of the page. Once both partners have come to the end of page 1, they should exchange their annotations and copy down onto their document any ideas that they didn't originally have. For example, if one student thinks the sigma in front of F is important and her partner didn't identify that, her partner needs to write that down on their own paper. The students then repeat this process until they have gone through both pages of the document. The students have approximately 15 minutes to work through this packet, so they should be reading and discussing each page every 7 or 8 minutes. 

I share with students that this activity has two purposes. The first is to practice reading detailed information in a relatively short amount of time. The AP Physics 1 exam has been redesigned to include more reading, so I want students to be able to practice reading and pulling out important information under a time constraint. The second goal is that students must grasp an understanding of the concepts, vocabulary, and equations used in Newton's Second Law discussions.

After I'm done giving the instructions, I reveal the pairs by simply reading them from the organized list. I have students move so they are sitting with each other, but since they are AP students I let them organize themselves and choose their own seat locations. Once everyone is settled I put the end time of the activity on the front board and begin to circulate the room. My circulation lets me know if students are on task and allows me to redirect students if I hear misconceptions or off-task conversations.


Small Group Second Law Problem Solving

25 minutes

As closure and an informal summative assessment, students have the rest of the class to start tonight's second law homework. The assessment is summative as it includes use of kinematics concepts that were learned earlier in the school year.  I call it informal because I don't want students to get nervous that it will count as a quiz or test grade. Since my goal is to assess their level of understanding and use of prior knowledge, I will collect and grade the assignment for accuracy at the start of the next class meeting. Not only do I want to give students personalized feedback on this homework assignment, I also want to check the pacing of the course and make sure my students are ready to move on to the next lesson.

Students remain with their partners from the paired reading activity as I pass out a copy of the homework to each student. This is an assignment that needs to be completed by each student on a separate sheet of paper, although they may use their partner as a resource while working in class. I encourage collaboration. Since students are paired based on ability, the "weaker" student is able to use the "stronger" student as a resource. It is also a goal of this strategy that the "stronger" student improves his or her knowledge by helping the "weaker" student work through the problems. As students work, I walk around to offer help or problem solve with the students. My style is to lead the students towards the answers, not just provide them with the correct answer. That being said, if a student is continually struggling and is in obvious need of being shown the answer, I accommodate him or her.  

This is our closure activity for today and it's meant to have students apply their newly learned knowledge from the paired reading activity. I am also trying to take a step towards a flipped classroom. I like students to have me as a resource when they work through problems, and I think it helps them build confidence. In the past I've attempted to do entire class periods of a full flipped classroom, but it's hard to hold the students accountable for digesting the needed material. I find that a combination of work time (that lasts right up until the bell rings) and in-class learning best fits the needs of my students.