# Day 80: Exploding Carts & Sound

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.

Physical Science: Sound

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.

# Day 135: Sound & Hardware Reactions

Physics: Sound

Students did a lab playing with various sound sources to start building some ideas about sound waves.

Chemistry: Hardware Reactions

Students went back to the nuts, bolts, and washers to test the ideas they built on limiting reactants in yesterday’s simulation.

# Day 133: Closed Pipes & Percent Yield

Physics: Closed Pipes

Students whiteboarded and discussed their results from yesterday’s lab on closed pipe resonators. They pretty easily recognized that, since the graphs of tube length vs. wavelength consistently have a slope near 0.25, 1/4 of the wave must have “fit” into the tube to produce a standing wave. This lab is traditionally used to find the speed of sound, but I always ended up just giving them length = wavelength/4, which bugged me. By having students use the lab to find that relationship, they only needed to use relationship between speed, wavelength, and frequency they found using snakey springs and the speed of sound, which they found using both a Direct Measurement Video and a Vernier microphone.

Chemistry: Percent Yield

Students continued working on their percent yield problems today. We spent some time discussing the physical meaning of the numbers they were using, especially the numbers in the balanced chemical equation and the molar masses since confusion about what those represent lead to a lot of the struggles students had on yesterday’s quiz.

# Day 132: Closed Pipes & Percent Yield

Physics: Closed Pipes

Students whiteboarded their results from yesterday’s lab and we discussed the results. Afterward, students started working on finding a relationship between wavelength and the length of an air column needed for a standing wave, using the speed of sound from the video to get the wavelength of a tuning fork.

Chemistry: Percent Yield

I introduced the concept of percent yield and students started working through some problems. They also took a quiz on stoichiometry, which didn’t go as well as I hoped. Looking at their work, I think a lot of students lost track of what all the different numbers mean, so I’m tweaking some lessons for later this week to try and get back to the physical meaning of the numbers they are using.

# Day 131: Speed of Sound & Speed Dating

Physics: Speed of Sound

After some time playing with the wave generator to confirm Thursday’s lab results, students used a Direct Measurement Video to produce a position vs. time graph and find the speed of sound. Tomorrow, they’ll put that speed to use in closed pipe resonators.

Chemistry: Speed Dating

Students needed just a little more practice to firm up their stoichiometry skills, so we did some whiteboard speed dating with problems similar to what will be on tomorrow’s quiz. I was really pleased at the number of groups who were really talking through problems , taking turns with the marker, and taking other steps to ensure that both students really understood what was going on.

# Day 48: Experimental Error & TIPERs Projectiles

Physical Science: Experimental Error

Students calculated the speed of sound based on the data they collected yesterday, then compared that to the expected result. Students found the speed using five different tuning forks, so we had some discussion about what it meant for those two different speeds to be close enough to be considered the same, which lead to some good conversation about experimental errors and why the values varied.

Physics: TIPERs Projectile Questions

I picked some questions out of TIPERs to help get my students thinking conceptually about projectiles. I was surprised at how many students struggled with a certain question where a ball is thrown upwards at two different speeds, and a student in the problem predicts that the faster projectile will reach the highest point first. Once I prompted students to sketch velocity vs. time graphs, the question ended up being pretty easy. It was a good reminder for my students to look at what tools they have, even when the problem isn’t about a calculation.

The faster object reaches its highest point in more time!

Today’s quiz on projectiles launched horizontally also reminded me why I love standards-based grading. Several students have been really working on solving problems with constant velocity and constant acceleration, and finally showed mastery when they applied those skills to projectiles today. I loved being able to give them credit for all the skills they showed, not just the big idea on today’s quiz.

# Day 47: Speed of Sound & Projectiles Practical

Physical Science: Speed of Sound

Students worked on the classic speed of sound lab using a closed resonance tube. Since this is one of the first labs my 9th graders do that has an accepted value, it provides a great opportunity for discussion on experimental error, which will happen once students finish the lab tomorrow.

Physics: Projectiles Practical

Students did a lab practical for projectile motion where they had to predict where on the ground a marble would land after being sent down a short ramp. In the past, I’ve used a cup, but most students hit the side rather than landing in it, so this year I used the school’s retired referral forms as carbon paper. I also pulled a jerk physics teacher move. After students got a successful prediction, I gave them a marble with a different mass and had them predict where the new marble would land without allowing them to make any new measurements. Most groups had to wrestle with it for a while and even try some calculations before realizing it should land in the same spot. I decided I need to keep this extra challenge in the practical when one student victoriously declared “Misconception changed!” after hitting their prediction with the new mass.

# Day 45: Exploring Sound & Projectile Calculations

Physical Science: Exploring Sound

Students did a lab to start exploring some of the properties of sound waves. They were very impressed by the tuning forks and a lot of groups went beyond the questions I’d posed and came up with more things to explore. One thing that drives a lot of people nuts about 9th graders is their lack of inhibitions, but I’ve come to love that uninhibitedness in this class because it means they don’t hesitate to share their excitement over an interesting observation, ask a crazy question, or do an extra experiment.

Physics: Projectile Calculations

Now that students know what the velocity vs. time graphs look like for a projectile, they dove into some problems. I’m continuing having them use graphical solutions a’la Kelly O’Shea where students solve from velocity vs. time graphs, rather than getting the kinematic equations. Compared to when I’ve given students the equations, students are much more aware of how projectile motion connects to the earlier constant velocity and constant acceleration models, and therefore less freaked out by motion in two dimensions.

# Day 44: Introducing Sound & Video Analysis

I was out for a field trip today, so no photos.

Physical Science: Introducing Sound

Students did some reading on sound waves today and started connecting it to what they’ve learned so far about waves in general.

Physics: Projectile Video Analysis

Students recorded videos of projectiles being thrown at different angles, then did some video analysis to see how that affects how high and how far the projectile travels.