Days 105-109: Energy & Pendulums

Physics: Energy

Students did a lab to introduce energy where they pulled carts up ramps at different angles, always raising the cart to the same height above the table, then measured the average force they needed and the distance they had to pull the cart for each angle. Then, they sketch force vs. distance graphs and see they always have the same area. The data was rough enough this year that students could see that a steeper angle required a larger force and a smaller distance, but the areas varied a lot. We’ve had a few labs lately where the data came out pretty rocky. I think part of what’s going on is it’s been tough this year in general for students to see connections between what happens in the lab and the physics concepts we are learning. If the labs are something disconnected from the rest of your learning, why would you invest time and attention into collecting high-quality data? We’re also at the end of a trimester when more students than usual are scrambling to raise their grades after an unusually challenging term and the February doldrums have been hitting everyone harder than usual, so students have less attention and mental energy to go around than usual. Aside from the final, we won’t have any more labs until tri 3, which is a good time for a fresh start. In the meantime, the other physics teacher and I need to do some thinking about how we will continue to draw connections between labs and physics concepts and make sure students have what they need to get good-quality data.

AP Physics 1: Pendulums

This week, we started working on simple harmonic motion. For the first activity, students used a video from Pivot Interactives that shows a pendulum, a cart attached to springs, and a spinning disk all in synchronized simple harmonic motion. Students made position vs. time graphs for each object, which always works well for some discussion not only of how the motion of all three is similar, but to establish some important ideas like the non-constant force and the repeating patterns in the motion of each object. After that, we dove into a deeper focus on pendulums by doing a lab to find the factors that affect the period of a pendulum. This model is going to be split over spring break, which got me thinking about how I currently have the unit structured. Right now, I have one standard for pendulums and one standard for springs. But, especially since I start by emphasizing how similar those two kinds of motion are, I wonder if it would make sense to instead have a standard about using multiple representations like motion graphs and energy bar charts to describe simple harmonic motion that includes both springs and pendulums, then a separate standard on the mathematical relationships and factors that affect the period which also applies to both pendulums and springs. That seems like it would better represent the different kinds of thinking I ask students to do over the course of the unit.

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