Today's test has been postponed for over a week as our school participated in state-wide testing last week. While it interrupts our study of objects in motion, that's not unusual in my course - we often move on to new ideas while providing time for students to prep for large, summative assessments like tests or presentations. In addition, the test segment of today's lesson is surrounded by some low-key class activities that help students stay connected to the current unit of study ("Objects in Motion").
Though the primary focus of today's lesson is a test, I'm confident that many, if not all, students will complete the test with plenty of time to spare. As an additional activity, with relevance to the new unit, I ask my students to try to "capture," with motion detectors, a constant velocity event. In this unit, we study both the "constant velocity" and "constant acceleration" cases of motion as we slowly progress towards the accomplishment of NGSS Performance Expectation HS-PS2-1.
Before they can meet this challenge, they need to see what the motion detector can do. I provide a demonstration of the motion detector from the front of the room with a set-up that looks like this:
I take a few minutes to explain how the motion sensor works and demonstrate how the sensing head is adjustable. Then I show students a few sample motions, without showing a constant velocity case. This graph was produced by simply pointing the detector at the board and rocking back and forth:
After these demonstrations, I tell students that, as they finish their tests, they can form small groups to quietly to try to meet the "constant velocity challenge."
Students now take a test on electromagnetics and waves. This has been re-scheduled a couple of times, so students have had a fair amount of time to prepare for this. The test reflects the same kinds of questions as a previously distributed mock quiz, solutions to which have been posted electronically over the past two weeks. This is my commitment to test transparency - no question on this test should look unfamiliar. The test contains questions on waves and wave mathematics, the relationships between frequency, wavelength, and energy of electromagnetic waves, radioactive decay modes, and both wave and particle models of light.
My classroom is set up in a U-shape with additional students sitting at a lab bench behind the U. I separate students who are too close making use of a second lab bench in the very back of the room.
Students take about 45 minutes to complete the test. Formulas and constants are provided and they are welcome to use a periodic table that is provided to them as well.
As students finish, they submit their tests to me and find a group to work with on the "constant velocity challenge."
Students self-assemble into small teams and wander out into the hallway to do their work. This is a welcome and spontaneous gesture on their parts, acknowledging that others are still focused on the test. Their challenge is to "capture" a constant velocity event, which prompts several conversations about what kind of evidence they should see on their devices. Another, more general goal, however, is to build capacity and comfort with the motion detectors. We will use these devices throughout the rest of this year and I would like students to be familiar with them.
Though the stated goal is to create constant velocity events, students inevitably wind up exploring other types of motion. Here, some students explore motion both forward and backwards.
Here's a sample of some wave-like motion. Note the sine wave position function (top graph) and the corresponding cosine-like wave of the velocity function (bottom graph). For my students taking calculus, this is particularly noteworthy!
After all students complete the test, students return from the hallway to work inside the classroom. These boys decide to create a rig that allows a piece of paper to slide down with a constant velocity. The personal investment is admirable even if it is at the expense of working with the motion detectors.
We continue in this mode until there are about ten minutes left, at which point I ask some student teams to come to the board to demonstrate what they've found.
In the final few minutes, students come to the board and re-enact successful scenarios of their own using my computer. I share two examples below. In the first, the student simply points the detector at the board and walks away at a steady pace for about five seconds, at which point he stops. The linear position graph is good evidence of a constant velocity and the flat-line after five seconds reminds us that velocity is about a change in position over time.
Another student team shows a similar strategy. In this case, I demonstrate to students how to use the software to get a best fit line which includes a report on the slope of the line. So, despite the wobble in the data, this event features a velocity of about .17 meters per second. This feature has great relevance and value to our continued study of objects in motion.