AP Physics 1

Day 83: Momentum-Time Graphs & Longitudinal Waves

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AP Physics: Momentum-Time Graphs

I’m taking a page from Michael Lerner and having my students use momentum vs. time graphs. Today, they worked on translating a p vs. t graph into a v vs. t graph, then do some interpretation. I also asked them about the meaning of the slope on the p vs. t graph, and I was pleased with how many students went immediately to the units to look for hints; in past years, my students needed much more prompting to look there. This year, I’ve been working a lot on getting students to look for meaning in graphs, and its fun to see them taking ownership of those skills.

pt-graph

Physical Science: Longitudinal Waves

Students whiteboarded some problems about longitudinal waves. I steered a lot of questions toward the parallels between longitudinal waves and transverse waves since it is usually a big leap for 9th graders to apply principles we discovered with transverse wave to other types. We also talked about why it might be useful to model something like sound that we know is a longitudinal wave as a transverse wave.

waves

Day 82: Board Meeting & Experimental Error

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AP Physics: Board Meeting

Students whiteboarded their results from the cart explosion lab to start building the momentum transfer model. I can tell its been a while since we’ve done a true model-building lab, so students needed some reminders about how to linearize or “translate” y=mx+b, but those skills came back pretty quickly. I did wish I’d had students linearize a bigger variety of graphs so far this year; a lot of students went straight to squaring a variable, so I may want to think about how to get more variety early in the year next year.

When we discussed the lab, a few groups had linerized based on a quadratic relationship and had a fairly large intercept. To decide whether the large intercept made sense, one student suggested exploding the plunger cart off empty space to get a mass ratio of zero and show the velocity ratio must also be zero.

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Physical Science: Experimental Error

We spent some time discussing yesterday’s speed of sound lab, focusing on error in measurements. I tried having students stand in different parts of the room based on how they thought frequency affects the speed of sound. When students were picking their spots, there was a lot of great conversation, including some contrasting frequency and speed, which was a great side effect. As we talked about error and what it means for values to be “close”, I had a lot of students ask to move because they changed their mind about what the answer should be.

Day 81: Exploding Carts & Speed of Sound

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AP Physics: Exploding Carts

Students worked on the exploding carts lab to build momentum. I rushed through the intro in my 4th hour since they didn’t have a chance to start collecting data, and students struggled with some pieces as a result, especially with what it looks like to graph ratios instead of numbers. I could also tell it’s been a while since we did a true model-building lab; a lot of groups got very focused on specific numbers, rather than the overall pattern. I need to do a better job of making sure we do those kinds of labs regularly.

explosion-1

Physical Science: Speed of Sound

Students used a closed pipe to find the speed of sound. As a result of some of the changes I made this year, students had a much better conceptual understanding of the lab than in the past. The calculation to get the speed didn’t quite seem to fit, though.

While students worked, I conferenced with students about their progress on a project. I met with every student, whether or not they had a draft. I really liked getting a chance to talk to each group; I think it gave a few students a push to stop procrastinating.


Day 80: Exploding Carts & Sound

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AP Physics: Exploding Carts

Today’s quiz took longer than I expected. One of my classes had some time to start collecting data on two carts in a mechanical explosion. They are plotting the ratio of the cart masses to the ratio of their speeds after a spring-loaded plunger launches them apart. I thought about using some probeware to measure the velocity, but went low-tech and had them use the ratio of the distances when the carts reached the end simultaneously. I like that this approach encourages students to start looking for patterns as they collect their data.

explosion

Physical Science: Sound

Students used tuning forks and wine glasses to explore some ideas about sound. Students made a lot of great observations and had good discussions with their lab groups and were able to bring some of that back to the whole-class discussion. One of the instructional coaches came by to give some input on helping my students adjust to my approach, and he had a couple of ideas I want to try. Since I keep relationships very qualitative in 9th grade, I ask a lot of questions with limited options, such as whether a variable increases, decreases, or stays the same when another variable changes. The coach suggested I have students physically move to a specific part of the room based on their answer to make it harder to opt out and to facilitate some additional conversations between students. I also like this because it is more obvious to students that we’re doing something different than going over answers like they’re used to. I tend to skip whiteboards in 9th grade, but my conversation with the coach has me thinking they would have some of the same benefits. I need to give some thought to how I can make time for whiteboards in a very tight curriculum.

I also got an idea from grading notebooks this afternoon. I use interactive notebooks, but have gotten very lazy about doing the left side/right side stuff. One of my students has started having a page for each lab, then using the facing page for a summary of the big ideas. That was a good reminder that the left side/right side can actually fit pretty well with what I’m trying to do in the class and I should be having students do those lab summaries.

sound

Day 79: Whiteboarding & Snakey Springs

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I spaced out and didn’t take any pictures today.

AP Physics: Whiteboarding

Students worked on whiteboarding elements of the two problems they worked on yesterday. One of the problems involved a block that slides up a ramp and became a projectile; students were either nailing the projectile portion, or completely lost. With an AP test looming, I need to remember to keep spiraling those old concepts back.

Physical Science: Snakey Springs

Students made standing waves and looked for a pattern in how many wavelengths “fit” on the spring. I found a lot of groups missed some of the standing waves, so we made a list as a class of the number of wavelengths they could make a standing wave with and students quickly recognized the pattern.

We also talked a little bit about assessments. After the magnetism quiz yesterday, a lot of students told me they thought it hadn’t gone well, but the most vocal students had perfect scores and the class average was 85%. After talking to students, I think this is related to my challenges engaging students this tri. The earth science assessments they took 1st tri put a lot of emphasis on factual recall, so the reasoning questions I shoot for are big shift for students. I need to think about how I can make it less intimidating to face a new scenario and need to take some time to think on the test.

Day 78: Flying Pig & Quiz

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AP Physics: Flying Pig

Today, I got out the flying pig for a lab practical. I had students measure the length of the string and the height of the cone, then use what they know about forces and circular motion to predict the time for the pig to make 10 revolutions.

pig

Physical Science: Quiz

Students took a quiz on magnetism. Afterward, we took a few minutes to review vocabulary for talking about waves that students learned during first trimester. It was pretty teacher directed, but I didn’t want to spend much time on terms students should have mastered earlier this year.

Day 77: Friction on Ramps & Energy Sources

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AP Physics: Friction on Ramps

Students whiteboarded a few of the questions from yesterday’s activity examining motion graphs for a cart on a ramp. Usually, most of my students rotate their vector addition diagrams so that the legs of any right triangles are parallel to the edges of their paper. Today, I didn’t see any rotated diagrams; I don’t think its a coincidence that today was also the first time I saw students consistently make very strong connections to the physical situation they describe. Now I’ve got a chicken and egg question; did students leave the orientation of their diagrams because they saw the physical meaning, or did they see the physical meaning because they left the orientation?

I also had students write a CER on whether friction is negligible in the data I gave them. I ended up really liking how small the accelerations are; the acceleration when the cart is moving upward is only about 0.05 m/s/s larger than the acceleration when the cart is moving downward, but it works out to a 25% difference, so students had some great conversation about uncertainty and how big a difference is big enough to matter.

 

 

Physical Science: Energy Sources

Students signed up for a topic and started researching different energy sources for a short presentation. Minnesota has a standard about comparing and contrasting different energy sources, so I have them research the pros and cons of their energy source. I need to think about what I want to have students do when the are watching presentations at the end of the project.

Next year, I might introduce this project at the start of the electricity unit. I like connecting the energy sources to what students know about electromagnetism, but I think I can maintain that connection if I make the project due after the unit has ended. I always have at least some students without internet access at home, so I try to provide some in-class worktime for the project. Since I do several simulation labs during the electricity unit, I could build in some worktime by encouraging students who finish the lab early to work on their research.

Day 76: Unbalanced Forces & Motors

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AP Physics: Unbalanced Forces

I borrowed an activity from my AP Summer Institute where students get a position vs. time graph and a velocity vs. time graph for a cart on a ramp. At the institute, we were tasked with finding the angle of the ramp and force of friction, but I decided to take a more conceptual approach and tasked students with writing an argument on whether friction is negligible. This was a little ambitious for their first experience with 2D unbalanced forces; I think it would have gone smoother if we’d spent some time practicing free-body diagrams and vector-addition diagrams for unbalanced 2D forces first.

cart-on-ramp

Physical Science: Motors

Students built electric motors, then did some simple experiments to drive home the connection between electric currents and magnetic fields. They seemed to get the connection between today’s lab, the electromagnet lab from Friday, and basic electricity generation.

I also took some time during class to talk with my students about what I want from them during a post-lab discussion and what I’m trying to accomplish during those discussions. I saw a lot more students participating in today’s discussion, both by raising their hands and by adding to their notebook entries. I’m planning to keep reminding them of what the post-lab time should look like, as well as share a little more about why I do things differently than the other 9th grade teachers. I need to remind myself that even if I’ve been in this routine for a full trimester, this is still new to most of my students.

 

Day 75: Whiteboarding & Electromagnets

/ Marta R. Stoeckel / 1 Comment

AP Physics: Whiteboarding

Most of my students were on a field trip today, so classes were pretty small. We whiteboarded some problems from earlier in the week on balanced forces in 2D. While the problems had a lot of calculations, I just had students whiteboard their diagrams and set-up, including some intentional mistakes. Later, I’ll post correct answers to the class website so students can check their calculations.

 

Physical Science: Electromagnets

Students built electromagnets, then made some observations about the magnetic field and strength of the magnet.To visualize the field, most groups opted for the compass over the filings, which reinforces my thinking earlier this week that I should start students with the compasses to see the bar magnet’s field.

This week, I’ve been thinking a lot about the fact that I’m really struggling to engage students the way I’d like, especially in post-lab discussions. The last couple of years, I’ve been able to get almost immediate buy-in from my 9th graders, but I think that’s because I only taught them during 1st trimester, when I got to set their expectations for high school science. Most of my students right now had a different teacher 1st tri, so I’m upending their expectations just when they were starting to get comfortable with high school and need to be much more intentional about helping students adjust. On Monday, I want to start with some conversation with the class about my observations and why I do things differently than their other science teachers. I’m also going to start thinking about how I can smooth the transition 3rd trimester, when about 2/3 of the class will be new to me again.

electromagnet

Day 74: Balanced Force Practical & Field Lines

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AP Physics: Balanced Forces Practical

I tasked students with figuring out the unknown masses in a set up with several strings at different angles. Groups found they had to be very clear about what they defined at their system, which as a nice element of the task. Different groups defined their systems differently and took different approaches to solving their vector addition diagrams, which lead to some fantastic conversations when groups who finished early compared results. I got really happy when I overhead a student slowing down his group down by telling them the process is more important than the answer, and even used the fact that I couldn’t remember the masses I used as evidence.

During prep today, I got a kick out of grading quizzes. I’ve been asking students this year to self-assess and do a short reflection on each quiz, and several students took that into specific problems on this quiz. These students wrote down some really interesting, specific metacognition right alongside their solutions without any extra prompting. It was really interesting to read. I might start having students do some journaling later this tri to explicitly encourage that kind of thinking.

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Physical Science: Field Lines

To help make sense of magnetic field lines, I had students connect gravitational energy to a topographic map of a hill, then went back to the magnetic field lines we saw yesterday to talk about magnetic energy. I haven’t done any forces with this class yet, but they are fairly solid on energy, so magnetic energy seemed to help ground the material in a way I don’t think forces would have. I also like that the topographic map helped link back to some of the map interpretation students did first tri in Earth Science.

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