I teach Physics First, meaning my physics students are freshmen. They’ve learned basic trig in their 8th grade algebra class, so they’re prepared for the math of a typical trig-based high school physics course. It’s always helpful to know your audience.
We’ve played with the standing wave demo, made standing waves on a snakey, so now it’s time to practice some theoretical problems. If there’s a struggle I see in more kids than anything else it’s that the kids don’t understand that a fixed string standing wave’s wavelength is the length of two “loops” of string.
5th period today wanted to find the frequency for the 2nd harmonic in a snakey. This was not part of my plan but how can you say no?
I would recommend eye protection next year, though. Just sayin’.
You know it’s a good day when physics students put your demo out on social media.
Struggling after yesterday to explain standing waves well, I borrowed the wave driver setup from a colleague. Duh! Why was I going for full-on theoretical when I had a way to make 3rd, 4th, heck, even 14th harmonics on a string?!
I gathered 4th period around the setup and asked what they noticed. They were amazed! “I notice 14 bow ties on the string.” and “I notice a high-pitched noise.” and “I notice these spots on the string that aren’t moving.” We pointed a strobe light at the string and I messed with the frequency of the light to the point of getting a slo-mo string progression within the wave. Then one kid asked what the wave would look like if she snapped a picture of it. I said, “I dunno, give it a try”. Soon, the girl was passing her phone around, amazed at the still image of a standing wave.
Kids wondered what would happen if they doubled or halved the frequency. So we did it.
Kids wondered what would happen if they increased the amplitude, went to a ridiculously high frequency (yeah, their ears regretted that one), or held on to a node. We were able to try all these things.
Vines may have been filmed, Snapchats may have been made. It was all a blur. 30 minutes later, after a little lesson and vocabulary, we had the strongest understanding I’ve ever seen among my students about how standing waves are formed. Kids were calculating frequencies and wavelengths for n-harmonics. I’ve never gotten to this point so fast with a class.
Is it possible that a good demo was really all I needed?
(Based on this picture, you might think I teach only girls. Not true. I teach only freshmen — they still think boys have cooties, so the groups stay well-separated until December.)
I’ve been struggling to get Moodle performing well for the dozen or so teachers on campus who use it. See that line of numbers at 7:40am where the ldavg numbers spike as compared to everything around them? That’s Moodle losing its damn mind.
Working on this server* has been a great intellectual challenge. I’m making just enough progress every time to be not discouraged. But the progress is lots slower than I’d like.
My Moodle server is hitting the CPU hard and making kids wait (like for minutes, man) to get their quizzes and homework. Since that’s just not cool, I’ve asked for and gotten help on the Moodle forums. Right now, I know the problem is that the server we’re on isn’t powerful enough to run Moodle. I need to make a change — maybe more CPUs or RAM — but need more data before I can know for certain what’s wrong. I’ve learned that Moodle, its underlying database, and the webserver software can all be optimized. But you have to know what you’re optimizing for. So every day, I log in and try to break Moodle so I can see the results.
A sysadmin friend of mine wrote me with some advice, closing with a quote I think could apply in physics labs as well as server troubleshooting, “The key, though, is to isolate the problem, figure out what it’s doing, and then try to generate a small reproducible case that you can work against.”
Other stuff today:
- Outlined the pneumatics training module for the robotics team I help coach. I’m working with a student to plan the weekly class. My favorite: the student suggested a troubleshooting class where we purposely set up problems for the kids taking the class to fix.
- Had a lot of flailing time in physics 4th period. Ugh, I hate that. It was my fault for being under-planned. But once I got my act together, we had a nice half hour of problem solving about waves reflecting off a fixed boundary. Kids were stressed by me not telling them if their answers were right. Slowly but surely, we’re going to build up their thinking abilities.
*oh, I didn’t mention? I was appointed the Moodle admin at my school. It’s a collateral duty I took because 1) I love Moodle, 2) I use Moodle in my class daily, 3) I NEED Moodle to work, and 4) I’m a little of a control freak.
We’re exploring how waves behave at fixed or loosely-held boundaries. I had the kids hop on to their first PhET sim to see the results. All told, about 10 minutes of diversion and lots of silliness surrounding making crazy waves. Before sending them off on their computers, I asked the kids to predict how an upright incident wave would reflect off a fixed boundary. Then I sent them to the PhET to figure it out for themselves. Repeat for loose boundary.
Also, I liked our warm-up problem today, from Ranking Task Exercises in Physics:
As a class, we’re working on writing good justifications for our rankings. It’s always tough to get teenagers to explain why they solved a problem the way they did, so I’m giving regular ranking tasks with justification to attack the problem.
All 4 sections took a quiz today. It’s the first quiz of the year and that meant my freshmen were a little nervous. We take assessments on Moodle during class, which gives them instant feedback but also seems to be a source of stress the first time out. I also require the kids to correct their wrong answers before turning in their work paper. Here’s a beautiful example of the process.
The directions for corrections are as follows: show your work on a separate sheet of paper. When finished, correct your mistakes and turn in the work paper. What do I mean by “correct your mistakes”?
- highlight the problem number,
- in pen, circle the point where you went wrong,
- classify your error as arithmetic, physics, rounding, or other (please specify),
- show the correct next step and solve the problem correctly from there.
Want to do the same but don’t have 1-to-1 laptops? This is just a more expensive/tech-heavy version of Frank’s Quiz Day approach.
Holy cow, it worked! After showing this and asking “what do you notice?“, the kids were so eager to make it happen. My picture was snapped just after two waves met in the middle of a Slinky, added their amplitudes, and destroyed the target. Moments before, the waves had small enough amplitudes to pass through the gates nearest the wave-generating students.
We walked away from the lab table with a lot of feel for how the superposition principle works.
Also, Frank has a similar video which makes me want a high-speed camera something fierce.
Speaking of waves, we had a pep rally today. Of course I recorded the Wave. Can you tell me the type of wave pictured? Its velocity, period, amplitude, and frequency?
In 6th period, we opened with a Ranking Task warm-up problem.
I asked for volunteers and two kids came to the board to provide their justifications:
- Kid 1 said “I multiplied amplitude (A) and wavelength (λ) to get velocity, then I ranked them by decreasing size.”
- Kid 2 said “I know the frequencies are the same, that v=λf, and that v is constant in a given medium. So, I ranked the wavelengths by decreasing size.”
Later while working classwork problems, I made the kids work silently for 15 minutes. If they had a question, they were to star the problem and move on. Some kids responded better to this “getting in the zone” move (even after I explained why) — some whispered for help from neighbors, others talked openly, and some even looked visibly shaken by being asked to focus individually for that amount of time. Clearly, the other teachers at my school don’t assign a lot of individual classwork. Or maybe it’s just that they’re freshmen. Afterward, we broke out whiteboards to work through questions in small groups. I think it went well because many students left with a completed assignment I might’ve considered ambitiously long in previous years.
[Note to self: remember to pull out the camera while students are actually in the classroom. Blogging my class practice daily takes a lot of remembering!]
In physics, we dug into our first classwork assignment. Most of my classes had an uninterrupted 30-45 minutes to work on a problem set on wave properties*. For the first time for many of these kids, I’m asking them to bring together multiple ideas to solve a single problem. Today, the big tricky problem was given a wave’s period and velocity, find its wavelength.
I prefer to NOT outline a bunch of problem-solving rules but rather watch how their natural (or previously-taught) styles emerge. Going around the room today, I saw a lot of interesting strategies, even for these relatively simple problems. Gotta get a few pictures tomorrow to share with y’all!
After school, the junior class, a group of which I advise, had a meeting. Here they are in the auditorium in the science building. The dean of students is sharing rules about driving on campus, off-campus (non)-privileges, and the importance of being on time for class.
Ask me sometime about my after-after-school project: training to be an outdoor ed faculty leader. There have been extreme heights involved, which scare the bejeezus out of me.
*I teach the semesters reversed from a traditional configuration AND teach Physics First (a true physics class taught to high school freshmen). Putting waves first saves mechanics till later in the year, mostly because I want to give their problem-solving skills a chance to mature in time for mechanics.