Meet Me In The Back of the Room; Bring Nothing

Friday was a homecoming assembly, so we had a shorter class. Plus my mind was on spreadsheets, again. We used to use this not-ideal way to sign up for parent-teacher conferences which meant that teachers often didn't know who was coming until a day or two before, that adults often signed up for conferences with teachers their students didn't have, and where everyone was fed ads all the time. So I found some code that made sense so that parents can't type over another parent's schedule, and now found a way that a teacher can own a Google Sheet that lets them see in real time who signed up for what times. It also will allow us to invite parents (I imagine like a pre-sale with concert tickets) before all the quick-fingered parents take all the times.

My year has been filled with spreadsheets because I'm trying to solve problems. I'm trying to make other people's lives easier. After a terrible year last year, I'm finding that making other teachers' lives easier gives me the most joy.

Yesterday, after a quick review of homework, we looked at a string vibrator and the different standing waves we could get on the string. The ability for students to touch it, and realize that it comes from constructive interference of wave on wave on wave on wave, was fun. Just playing with the string, touching the string, letting the kids try different frequencies, make the standing waves so much more real. I like that they get to experiment about when standing waves happen. Part of me wanted more set ups so more students would feel comfortable making their own hypotheses, and part of me was so happy to be there to guide the exploration and not let students get fooled by almost standing waves.

Today, we whiteboarded one quick question on the standing wave:

Then we used boomwhackers to play with two open ends and one open end/one closed end standing waves. I was so tired because I had a school event until 8:30 PM last night, and then we had to report for a staff meeting at 7:30 AM this morning, so I feel my whole schedule feels off these past two days.

We did one of my favorite introductory problems today in AP Physics 2. It's a series of two problems that lulls them into complacency:

Oh, you're asking how the wavelength will change if the frequency changes? Oh, then the velocity must be constant.

Oh, you're asking how the speed changes when the frequency changes? Oh, then the wavelength must be constant.

One of those reasonings can't work, but they're not used to thinking deeply about how three quantities change. They're not used to justifying why what stays constant stays constant.

This is the big jump for AP Physics 2—sometimes, I think it's the whole point of the ideal gas model & phase diagrams for a gas. 

Oh. they also fooled me with a 440 Hz tone for the bell, and I let them out two minutes early. I gave them too much knowledge.

After a little practice of wave superposition, I showed how waves reflect off fixed and free ends. We then went outside to watch two slinkies of different mass densities so we can see how waves reflect off the boundary between two media. I really like this particular simulation of reflections in different media to show in detail how the reflection happens. (That simulation also does a great job of reinforcing how every wave both is reflected and is transmitted at the boundary.) I then gave them time to work on a whole mess of problems to practice what we've learned.

My AP Physics C class all wanted to go to a college visit tomorrow during my class, which is when my test on kinematics was scheduled. I was OK to move it, but we talked about how we gotta schedule things early. It turns out some of them didn't know until the day before, so I got the college people to give better notification to students.  

I embraced concept, then definition today in a slightly new way today. We had already learned beats, but we had no way to explain it. After a bit on the Doppler Effect, we went into the hallway and watched a crest and a crest overlap as well as a crest and a trough. We practiced that with a few basic problems, and then looked at two waves with almost the same frequency. They seem to have constructive interference at one time and then it seems to go to destructive interference a little later. That explains the LOUD to soft to LOUD to soft to LOUD to soft we heard when we played two waves of slightly different frequencies. We can explain it now!

I really liked that a phenomenon they saw, they understood, that they even had a name for, did not yet have an explanation. But we can get to explanation with just a little bit of model building. And I don't have to walk them the whole way. I can just show the problem, and ask them what would happen, and let them tell me what that seems like they've seen in the real world.

(I showed the problem using this Desmos simulation that I made. I've included a picture below.)

That look of understanding, that look of realization, makes teaching so worth it. When I can make a terrain that they can then use, with their own creativity, to come to understanding, well, that's the best.