Day 103: Energy Practical & Explanations

AP Physics: Energy Practical

I tried a new lab practical for energy in an effort to integrate rotation and spiral back to some old ideas. Back in December, students measured the launch velocity of a marble, then predicted where it would hit the floor. Today, I had them use conservation of energy, including rotational kinetic energy, to find the launch velocity of their marble, then predict where it would hit the floor. I saw a lot of students pull out their old work, including their lab from December, to help remind themselves how to do the projectile portion of the problem, which is exactly what I hoped they would do. I overheard several students talking about how much they liked looking at an old problem through a new lens, as well as seeing how old ideas fit with the new ones.

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Physical Science: Explanations

Students practiced making predictions and writing explanations using Newton’s Laws. I showed students some videos and clips, including one from Smarter Every Day and an animation of the Mars Pathfinder landing, then had them write an explanation individually, followed by a revised explanation with their whole group. I was struggling more than usual to keep my students focused, but part of the problem might have been the English test next hour and the pep fest this afternoon. I’ve got some demos I’m planning to have students write explanations of as warm-ups, and I probably would have been better off using the demos today, then using the videos as warm-ups.

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Day 102: Gallery Walk & 2nd Law

AP Physics: Gallery Walk

I ended up having students do a gallery walk for yesterday’s problems.

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Physical Science: Newton’s 2nd Law

Students worked on a version of the modified Atwood’s machine lab for Newton’s 2nd Law. While I have students make a graph, we don’t go much deeper than whether each relationship is direct or indirect. I spent more time on the pre-lab discussion today than I have for most labs with this group, and I feel like that paid off with more confidence while they were actually working in the lab.

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Day 101: Conservation & 1st Law

AP Physics: Conservation Problems

I left my AP classes to chaperone a field trip, so they worked on some conservation of energy problems. I’m not sure how I want to go over the problems yet; based on what I saw in class yesterday, they are pretty solid on making bar charts, but are a little shaky on connecting them to specific quantities. I might do the mistakes game, focusing on setting up the equations.

Physical Science: 1st Law

Students did a lab based on various tricks using Newton’s 1st Law where they focused on writing good explanations of WHY the trick worked. For conceptual development, I don’t like this as much as the bowling ball and mallet lab I do in physics, but I like that they get a chance to practice explaining things using Newton’s Laws, which is important in helping them connect the science to the upcoming engineering project. Next year, I might try to add a day to this unit so we can do some version of both.

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Day 100: Rotational Energy & Weight

AP Physics: Rotational Energy

Students whiteboarded yesterday’s problems and we spent some time discussing how changing the system changes the LOL diagram. I picked a problem where a block on a spring becomes an upward projectile and a second where a block is launched by a spring up a track; I really liked using this pair since it drives home that path is irrelevant in conservation of energy.

Afterward, I had students use conservation of energy to predict the velocity of a marble at the bottom of a ramp, then we measured with photogates. Their prediction was off by about 60%, which I used as motivation to introduce rotational kinetic energy to account for the “missing” energy at the bottom. When students saw the actual velocity, they were quick to attribute the difference to friction, even after seeing the percent difference, so now I’m wondering if there are other good ways to rule out friction. Maybe time the marble down the track, then compare the acceleration to the component of gravity along the track?

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Physical Science: Weight vs. Mass

Students weighed hanging masses on spring scales to find a relationship between weight and mass. We moved this to the start of the unit since its the one thing we do with forces that doesn’t fit with our engineering project, but I feel like weight ended up separated from other important ideas from forces. As we dig more deeply into forces this week, I’ll make sure I circle back to the concepts of weight and mass, so I may decide this sequence was okay after all.

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Day 99: LOL Diagrams & Motion Detector

AP Physics: LOL Diagrams

Students went from bar charts to full LOL diagrams today. I am really coming to appreciate one of the worksheets from the Modeling Instruction curriculum that has students make LOL diagrams using several different systems for the same scenario, which really nicely illustrates why identifying your system matters. Students took to this easily enough that I think bar charts and LOL diagrams are a spot where I can pick up the pace a little next year.

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Physical Science: Motion Detector Lab

Students walked in front of the motion detector to reproduce the graphs they worked on Friday. Since we ran out of time on free fall day, I also showed a clip of Brian Cox when he visited a giant vacuum chamber to drop a bowling ball and feathers.

 

Day 98: Mistakes Game & Motion Detector Lab

AP Physics: Mistakes Game

Students played the mistakes game with energy bar charts. My 2nd hour had a sub, so I’m not sure how things went. My meeting got done early, so I made it in time for my 4th hour class. This group is usually quieter during discussions, and they were much more nervous about doing the mistakes game without me since they were not confident they would get the right answers, but I was able to sit back while my students ran the show.

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Physical Science: Motion Detector Lab

Students worked on describing motion based on position vs. time graphs. On Monday, we’ll get out the motion detector to check their descriptions. They had a sub, so I’ll find out then how things went.

Day 97: Energy & Free Fall

AP Physics: Energy

We had a board meeting on the two energy labs from this week. The kinetic energy groups tended to get very nice results; I had them check their model with multiple cart masses and ramp angles, and they saw the results were consistent. I had the elastic energy groups use multiple springs, but they didn’t see as clear a difference between the slopes as I would have liked. I’m wondering if the results would be less muddy if I had them plot gravitational potential energy on one axis rather than just plotting height. I shortchanged some of the pre-lab discussion, and I think that lead to students forgetting to do things like measure the cart’s starting height or measure both the starting and ending height from the same end of the cart.
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Physical Science: Free Fall

I got out washers, manila folders, and a few other things and tasked students with determining what affects the time an object takes to fall. In the pre-lab discussion, a student suggested the fluid an object falls through could affect the time, so next year I might make sure I have graduated cylinders and some different liquids available. I offered to grab materials if a group wanted to try that, but I think asking me to get stuff felt like an extra hurdle.

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Day 96: Angular Momentum & Average Velocity

Today, I was chaperoning a field trip so I missed most of my classes.

AP Physics: Angular Momentum Quiz

Students took a quiz on angular momentum, then worked on finishing yesterday’s lab. One of the problems is based on a story that before jumping a motorcycle over the Snake River Canyon, Evel Knievel said his biggest fear was accidentally hitting the brakes in mid-air. I was back in time for 4th hour, so I showed students a demo of the problem using an RC motorcycle.

Physical Science: Average Velocity

Students worked on some problems interpreting position vs. time graphs. One of the questions asks them to invent average velocity by coming up with multiple ways to define the average velocity, then use each approach to make a prediction and decide which definition is the most useful.

Day 95: More Energy & Sledding Problem

AP Physics: More Energy

I split the class in half with some groups doing a lab for elastic energy and others doing a lab for kinetic energy. The groups looking at elastic energy looked for a relationship between how much a spring launcher is compressed and the maximum height above the table the launched cart reaches. The groups doing kinetic energy looked for a relationship between the starting height of a cart above the table and the speed at the bottom of the track.

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Physical Science: Sledding Problem

I gave students two position vs. time graphs that I said describe two people sledding, and had them do some interpretation. Students started by describing the motion of each sledder, then identifying where they collided. Finally, each group prepared a CER for who’s fault the collision is, which we then used for a short philosophical chairs where students made their case to the rest of the class. This lead nicely into a brief discussion of assumptions and they role they play in generating an explanation or a claim in science.

The sledding story made the coordinate system tricky for students. I wish I’d spent time discussing the descriptions of the motion so we could make sense of them moving in opposite directions.

sledding-graphs

Day 94: Intro to Energy & Motion Graphs

AP Physics: Intro to Energy

Students picked a height to raise their cart above the table, then made a rough force vs. displacement graph and repeated for additional angles. We compared the areas of the graphs, then defined that area as the change in gravitational potential energy. The biggest hangup is that students are so used to graphing their data that I have trouble getting across that I want a description of an individual run, instead. I might try some additional discussion prior to the lab next time.

As a side note, it was interesting to watch what looked like some gender dynamics in one of my classes. All but one of my all-male groups picked a fairly high point to raise their carts to, then used very steep angles, getting their tracks nearly vertical. The one all-female group in the class picked the lowest point they could, then did very shallow angles. I also had one mixed-gender group, and they picked both a height and angles right in the middle.

 

Physical Science: Motion Graphs

We finished whiteboarding results from the video analysis, following each up with a similar case on the motion detector. I should have broken up the discussion a bit more, which reinforces what I was already thinking about with going low-tech for constant velocity, then introducing video for constant acceleration. I also had students move away from their lab tables for the group discussion, and talked a bit about why I was doing it, and students were much more focused on the whole-class discussion this time.