Practicing Projectile Motion
Lesson 6 of 7
Objective: Students will be able to solve and explain problems in projectile motion.
Throughout this unit students have learned the fundamentals of projectile motion, so today the goal is to practice application of that knowledge. The lesson starts with a warm-up (that comes full circle in our closure) before students collaboratively solve problems (SP5). The students share their solutions (SP6 & SP8), and then I bring closure to the warm-up that started our lesson.
When students walk into the classroom I have a warm-up projected for them on the front board. As soon as our bell rings, I read the problem aloud and then give students time to try and solve it. My reading the problem reinforces that class has started and gets any straggling students focused. I do allow collaboration during the work time, since I think it's important that students get to talk through their thought processes. It is also an expectation that students show these thought processes (even if they use a calculator) with written work in their science notebooks to use as a reference later in the lesson.
I walk around during their work time to informally assess student's work and conversations, but I will not tell a student if their answer is right or wrong. We are going to go through the solution as our closure and I want students to get used to not having immediate feedback. It's my goal that this delayed feedback will force students to double check their answers, or possibly amend their answers throughout the class.
This problem was chosen specifically because it is a horizontal launch, and we've been focusing on projectiles launched at an angle over the last few days. Students need to remember, as we review projectiles today, the assumptions that can be made in a horizontal launch.
Today's class will use my collaborative solution & teaching strategy as way for students to review projectiles. Students are each given a different problem from a set of projectile practice problems. These problems are taken from our Serway & Faughn textbook, and are problems that I feel are most representative of the test questions. To save time, students stay at their lab tables and I give each group one of the problems with its answer. Students always get excited when they see that the answer is given, but my goal in this activity is to see how students arrive at that answer. The majority of possible points on the free response portion of an AP exam comes from justification of the answer, so that justification process is the emphasis of our activity today.
The problem that each group receives is random: I literally walk down the center aisle and give the group whichever problem is on the top stack of my pile. My expectation is that students take about 10 minutes and actively work together to write down the solution on the paper I passed out to them. Without giving the students too many details, I tell them to be prepared to not only show their solutions, but to also be able to explain their solutions. Also, I encourage students to use pen as they work. Using pen keeps them from erasing, so even if they make a mistake or change their thinking, I can see evidence of their entire process.
As students are working at their lab tables, I walk around and ensure that everyone is engaged in the discussion and thinking critically about their assigned problem. I am willing to give students hints as I observe, but my feeling is that by this point in the 2-D Kinematics Unit students should be able to independently work through these problems.
Students Share Solutions
After the collaborative work time is over, I share with students that they will be presenting their solutions to the rest of the class. Each group will come forward, put their problem with the solution under the document camera, and explain that solution to the rest of the class. The goal of this activity is to show students the variety of problems that will be on the 2-D motion test.
Because my students are sometimes shy, I ask if any groups volunteer to go first. There is always at least one group that wants to get the presentation out of the way, so I choose them and applaud them for being so willing. These first group of students walk to the front of the room and place the problem with their solutions under the document camera. One person from the group must read the problem aloud so the entire class becomes familiar with that problem. A second student should explain any diagrams that were drawn and the list of given information. Finally, a third student from the group will verbalize the solution that has been written on the paper. Once the solution is appropriately provided, I ask the class if they have any questions for the group. If someone from the class does need to ask a clarifying question, or if I need to ask a clarifying question throughout the solution sharing, I expect that any presenting group members who haven't participated yet will answer these questions.
Once that first group is finished, I let them pick which group they'd like to share next. This chosen group comes forward with their problem and solution, shares, and appropriately answers questions as the last group did. The process repeats itself until all problems have been shared. If students took good notes throughout this activity, they now have a great study resource of new questions with solutions.
Finishing our Warm-Up
It's now time for me to relieve the students' curiosity and share the answer to our warm-up. They should still have their work out on their desks, with the goal being that they compare their individual solutions to my solution. I show students that we are given a horizontal velocity and height, and our goal is to solve for time and horizontal displacement. Students must remember that this is a horizontal launch, so I ask the class what assumptions we can make from the problem. Because we just went through practice problems that included horizontal launches, I wait to move on until someone contributes that the initial velocity in the vertical direction is zero.
As soon as the class remembers that assumption, I share the rest of the solution. We don't have much time so I get right to the "meat" of the solution. The point of my direct explanation is to leave time for students to ask questions. Because there is a unit test during the next class meeting, I don't collect the students' work. My hope is that they can use this practice problem as an additional study resource.