Today in AP Physics 2, we discussed the Second Law of Thermodynamics from the perspective of entropy as a measure of the probability that a certain state will occur. Groups finished their analysis of their data from yesterday’s activity. I then shared the analysis of the data aggregated across all of the groups. It dramatically illustrated how quickly the entropy of the system increases and how it does not decrease with a sufficiently large sample size.
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Today, as AP Physics 2 starts our last week of thermodynamics, we tried a new activity that I learned at this summer’s AP Physics 2 Summer Institute. I’ve mentioned statistical mechanics a few times throughout our exploration of thermodynamics and wanted to provide students some insight into this area of physics and a different perspective on the concept of entropy. So, we modeled the diffusion of a two-gas system with dice. Each group started with 2 sets of dice of different colors. The initial state was all of one color on one side and all of the other color on the other side. They rolled the dice. A die is moved to the other side if it is a “1”. After each roll, they count the number of nice of each color on each side and record the data in a spreadsheet. The spreadsheet calculates the number of microstates for the particular macrostate and the entropy. After class, I aggregated all of the data from all of the groups. We’ll discuss the aggregated results tomorrow. Thinking of entropy as a way to quantify the probability of a state occurring is a powerful perspective.
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After characterizing their system yesterday (specifically, determining the volume of the system), today, students measured the temperature, pressure, and volume as they performed a thermodynamic cycle. This idea of characterizing a system in preparation for a lab is emerging as a theme in this new course. The results were excellent. The equipment performed well and the students executed their cycles with precision.
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A lab I started doing last year was the Heat Engine lab from Advanced Physics with Vernier – Beyond Mechanics. We did the lab again this year, but entirely on the LabQuest 2 instead of with LoggerPro. I’m consistently surprised with how much can be done entirely on the LabQuest 2 (specifically, integrating the area enclosed by the thermodynamic cycle in this case). The first part took longer than expected as students familiarized themselves with the equipment. We also had to troubleshoot some old equipment and make some replacements of hoses and stoppers that didn’t leak.
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As I’ve mentioned before, we’ve been using InfuseLearning for Peer Instruction. I’m using InfuseLearning over some of the alternatives because of their support for “Sort in Order” questions (i.e., ranking tasks) and “Draw Response” questions. The ability for students to respond with a sketch is huge. For example, today I presented students with a description and sample pressure vs. volume graph of a thermodynamic cycle. The sample graph was incorrect and they had to respond with the corrected graph. Here are some sample responses:
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Today’s whiteboarding presentations for AP Physics 2 focused primarily on heat engines. Sometimes a group just nails a whiteboard. This group so clearly presented the key concepts of a thermodynamic cycle; specifically, the graphical representation of the net work done by the cycle. I had to get up and take a photo.
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Today in AP Physics 2, I introduced heat engines. While perhaps not an huge part of the new curriculum, heat engines nicely connected everything that we’ve been studying so far in the thermodynamics unit and set the stage for our investigation of entropy next week. I also think it is fantastic for students to leave with a basic understanding of how an internal combustion engine works since very few students understand this in my class. This slow-motion video of a couple of cycles of an internal combustion engine is fantastic!
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Today I was at a professional learning day for our district’s Digital Learning Initiative. I wanted to continue to have students practice constructing strong explanations based on evidence. So, since I was inspired by an activity modeled for us last week by Brett Moulding, I left the following assignment for students to complete while I was gone:
Target: make observations, ask questions, design investigations, and construct explanations for phenomena.
Observation (5 minutes)
Watch the following video.
Capture your observations in your notes. Apply existing models to help you gather data.
Investigation (15 minutes)
Ask questions. Design additional investigations and perform them to answer these questions. Make additional observations. Apply existing models to predict and develop evidence. Analyze data.
Explanation (10 minutes)
Construct an explanation of the phenomenon. Discuss proposed explanations with your group. Develop arguments from evidence. Apply existing models to develop evidence. Construct explanations at both a macroscopic scale and an atomic scale. Use appropriate terminology.
Communication (5 minutes)
Individually, write your own explanation (addressing both a macroscopic scale and an atomic scale) and submit it for this assignment.
Discussion (5 minutes)
Share your explanation with your group. Provide feedback to each other on the strengths and weaknesses of the explanations. We will discuss as a whole class tomorrow.
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Inspired by last Friday’s professional development where we focused on students making observations, asking questions, and constructing explanations for phenomena; I wanted to provide my AP Physics 2 students with some practice in this area. We started with a computational model of two gases in the same container. One gas initially has a higher temperature than the other and is positioned on one side of the container. As the model runs, students can observe the interactions among the atoms of the two gases and the resulting histogram of rms velocity. Students made observations in groups, defined additional questions to investigate, and changed the parameters of the model accordingly. After plenty of time to investigate and discuss as a group, students individually wrote their own explanation of the phenomenon in the span of five minutes. Each group than read their explanations to each other, provided feedback, made revisions, and selected one explanation to share with the entire class. Each group than shared their selected explanation with the entire class and the entire class, including me, provided feedback. If students didn’t comment on their own, I took the opportunity to highlight explanations that cited our existing models as evidence, explained the phenomenon from both a macroscopic and atomic perspectives, and correctly used the vocabulary we have been practicing in our study of thermodynamics.
After this discussion, student then looked at a modified computational model where the two gases are separated by a barrier that prevents each gas from crossing to the other side of the container but allows collisions between atoms across the barrier. We didn’t have time to go through the entire observations, additional investigations, and explanations cycle again, but students did connect this model to heat transfer via conduction.
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Today AP Physics 2 students discussed their observations and explanations from the heat transfer lab. Different groups did different parts; so, it was important to spend some time sharing. I missed the lab, but I was able to wander around and see the data and graphs that were exported from Vernier’s Graphical Analysis app that ran on the Chromebook and viewed data from the LabQuest 2 interfaces. This was their first time interfacing the LabQuest 2 with their Chromebooks and it went well even without me there! Here is a a graph from a group observing the effects of heat transfer by radiation on two cans (one painted black, one silver) of water.
##thermo ##equipment ##tech ##labquest2 ##chromebook