Constant Velocity Lab Practical
Lesson 10 of 10
Objective: Students will be able to predict the intersection of two objects by using data collected from each object.
Student Test Reflection
The goal of this lesson is to do a lab as a team to assess students' knowledge of the content covered in Unit 1. The closer students get to the correct answer the better their grade is. The lab is set up that there are two cars with different speeds; one starting at 0 meters and the other starting at 0.5 meters. Their goal is to find at what position the cars will meet. This lab practical pulls out multiple science and engineering practices from NGSS and is a good way for students to work with the team that they have be learning from and working throughout this unit. Students will use skills in science and engineering practices of planning and carrying out an investigation (SP3) as they figure out how to run an experiment with two cars (only having one at a time) to find out where their paths will cross as well as the practice collecting and analyzing data (SP4). After they have collected data from both cars, they will use computational thinking to graph their data or to use equations to solve for the location that the cars cross each other (SP5) and communicating all of these aspects in writing (SP8).
To begin class, I tell students that I am about to hand back the tests they took in the previous class. But before doing so, I ask the students to take out a note card from the table bin and write their name on the front side; on the backside I ask them to write the letter grade they think they got and a sentence of why they think that. Once done, I hand back the tests and ask them to look through every page since I made notes to them on why they got some sections wrong. When students are done looking through their tests, I ask them to write a second sentence on their note card stating if their actual score agreed with their prediction. If their prediction did not agree I ask them to explain why. I then collect the cards and the tests from the students. Some of my students cards are shown below.
I do this activity with the students because it is their first major unit test and their results often comes as a surprise to many. This writing prompt helps students reflect about how much they need to prepare for physics tests, either by doing more preparation during the unit, by coming in for help when they don't understand material, or by deciding what material to focus on when studying. I think that this is important for students to recognize early on in the semester areas where they can improve their study habits.
Lab Practical Prompt
When students have finished reviewing their tests, I pass out a copy of the lab practical prompt (Unit 1 Constant Velocity Lab Practical) to each table group. Then I ask for one person from each group to read the prompt to the group aloud. When every group has finished reading or listening to the prompt, I ask them to tell me what they are going to do today. Students will give me a response like we are going to try to find the point where two cars meet. After they give me a summary of what they are going to do, I show them two of the cars and demonstrate that the faster car will start at 0 meters and the slower car will start at 1 meter. I show them the motion of the two cars and how they intersect. At this point I also tell them that 10 points is for how close their prediction is to the actual distance and 15 points is for the work they show on the back of the page. The goal of this activity is for students to use the graphical, diagrammatic, computational and verbal models used throughout the constant velocity unit to determine where two carts at different speeds, but starting at different locations, will meet.
To make sure both of the constant velocity cars have different speeds, I replace one of the batteries with an aluminum slug (a dummy battery). Each group is only allowed to have one car, either a slow car or a fast car, at a time; they can use each car for a maximum of 15 minutes. When a group with a fast car is ready to switch, they swap cars with a group with a slow car. Students work in the hallway where there is more room. After the explanation of what to do, I provide time for questions. Once all questions have been answered each group receives a car and gets started. Students then take 4 meter sticks and a stopwatch out to the hall and begin; I set the timer for 15 minutes.
Once students are in the hallway and the timer is started, I check in with groups and remind them that 15 points of their grade is for the work they show on the back. They should include data tables and graphs. I walk around the hallway making sure that each group has all its members nearby and that teams are not talking to each other. When students are done with their car, I ask them to wait until the other group is done.
While students are in the hallway, they are recording positions for their cars at each second interval by placing post-its on the ground and then reading where it is from the meter sticks they have set up. Students will collect a couple trials of data for each cart so their data can be more accurate. Some students will be inputting data into Plotly, while others are writing down data on the back of their papers to show work.
Once both groups are done with their measurements I have them exchange cars. This should happen within 15 minutes. The timer is started once again for 15 minutes. As students are done with measurements and data collection, I take the cars and return them to the front of the classroom. I tell students they have until there are 15 minutes left in class to work on finding their prediction. At that point, all groups must either start testing or be in line to test their cars.
Students Test Predictions
When students are ready with a prediction, I have them set up their two cars at their respective locations and have two students get ready to start them. I say "3,2,1 GO" and on "Go" they start the cars. Because it happens so quickly, I place a post-it note on the floor where the cars intersect and then record the numerical value of the intersection point on their paper. I calculate the percent difference for them and match it to with how many points they get for how close they were. As long as there are no students waiting in line, I calculate the percent difference right away; I grade the back of the page later. When students are done, I tell them they can watch other groups' trials until the bell rings.