Constant Angular Acceleration

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Students will develop an understanding of constant angular acceleration.

Big Idea

Today students learn to love constant angular acceleration equations when using them to solve circular motion problems.


During the previous lesson, students defined the angular quantities of displacement, velocity, and acceleration (in preparation to address HS-PS2-4), so today students will be introduced to constant angular acceleration. The lesson starts with a review of constant linear acceleration with a ranking task (SP6 & SP8), before students engage in a short video activity that introduces constant angular acceleration (SP5). Finally, students get a chance to practice their knew knowledge with an informal one word closure activity and collaborative problem solving.

Introduction with a Kinematics Review Ranking Task

10 minutes

Today's ranking task introduction is meant to refresh students' thinking about linear, constant acceleration equations. I always have any introductory activity ready to go when students walk into my classroom to help with time management, so the kinematic review is projected onto a screen at the front of the room when students enter.

Once the students are settled, I read the instructions to the activity. My reading of the instructions is to ensure students understand that class has started! After I've finished, I emphasize to students that they should work individually and take about 5 minutes to rank the accelerations, explain their reasoning, and then assess their level of confidence. During these 5 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 5 minutes are over, I am back at the front of the room and reveal the answers by writing them onto the front screen:  E, F, A, B=C, D. I always start by asking if anyone got all of the situations in the correct order. Since my students are rock stars, inevitably there is always at least one who did and is willing to admit it. It's that student that I then ask to explain why they ranked the situations the way they did. 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 of that missing information so the whole class has a complete understanding. I end the introductory activity by asking if there are any questions and then collecting the ranking tasks. 

Constant Angular Acceleration Video Activity

15 minutes

Because there are so many great resources out there and I had an introduction that was teacher-led, I've decided to use this video to present the equations for constant angular acceleration. Before I start the video I make sure my expectations are clear. Students need to be sitting quietly, listening and watching the video, and taking notes on meaningful material. To me, meaningful material includes any reference to previously learned concepts, equations, vocabulary, and examples. I am telling my students these expectations as I'm on my way to start the video.

As we watch the video I pause it in several places to give my students an opportunity to process and internalize this new information. For example, I pause the video at 22 seconds and ask students if they remember the horizontal kinematic equations. I give students about two minutes to think about these equations and try to write them in their notebooks. Then, students get an additional two minutes to recall the equations while working with those students seated around them. My goal is to activate students' prior knowledge and informally assess their ability to recall equations from a few months prior. Once time for them to work together is over, I resume play of the video and students can check their work with the actual equations presented in the video.

I use a discussion guide to remind me where to stop and what important material or questions I want to share with the students. When I pause the video I'm somewhat flexible in our discussions, meaning if a student has questions or needs further explanation I take the time to do that. I always write down the equations on the front board so that students are sure they have copied them properly.

Closure & Homework

20 minutes

Before I allow students some time to work on their homework, I ask students to do a quick closure activity in which they will debrief about today's new material. I start by asking students to sit quietly and think of one word that describes today's class. I circulate the room to make sure students are just sitting and thinking - not writing, not organizing materials, not packing up to leave. This quiet reflection period should last for about a minute. Then, I direct students to turn to someone near them and share their answers. The exchange between partners or trios should take anywhere from 3 - 5 minutes. 

While students are debriefing together, I walk around and ask students to share their words with me. I stop and chat with different groups to gauge their level of understanding and to see if I can answer any questions. I take this information and use it to reflect on how I need to adjust my teaching practices (Did I go too slow? Too fast? Is this too much information for 1 day? etc). To make sure I have contact with each group, I also pass out tonight's homework as I'm circulating.

I choose this homework assignment because it asks students to practice applying the angular kinematic equations to a variety of different situations. As I hand students a copy of their homework, they are expected to start solving the problems with their debrief partner or trio from the one-word-closure activity. I encourage students to work together, and it's ok if one student does the even problems while her partner does the odds (as long as they switch and share solutions before the assignment is due). This type of collaboration eliminates some of the stress on the students while still ensuring they are able to solve a wide variety of problems. The class officially ends when the bell rings.