# Day 12: Representations and System Analysis

Thursday, Sept 14

Day 2 of getting after this cold with my arsenal. I am feeling significantly better, so the assault continues. Also found a solution to the problem of occasionally accidentally drinking down a whole peppercorn. Turns out if you only open the spout on the cup part way, tea still comes out, but peppercorns do not! SCIENCE!

Physics: I love this class. It challenges me the most as a teacher, and the kids are the most demanding and with the widest range of abilities, but I feel so alive in front of them. I have to work hard to take them with me. Today we went over the quiz and talked about how there are different ways to approach a problem, either through doing physics calculations or just thinking about it. This really blew their minds that you could figure out the answer by thinking about what average means. It was a question about average velocity. The object started from rest and 1s later was at 10m/s, what is the average velocity? A LOT of the students said 10m/s, so I asked them if they took two tests and scored a 50 on one and a 100 on the other if their average was 100. There was a lot of stunned realization happening. After going over the quiz, we reviewed the homework, which was about free fall times and distance and then got back to what I really cared about: multiple representations.

I got the question, “When would you use a position-time graph?” and I said something about motion detectors (which we don’t have) that was a total fumble. I need to get a better answer to that question. When WOULD you use a position-time graph? I spoke to a colleague about this at lunch and he helped me see that it’s not about using a position-time graph, specifically, it’s about understanding how things are related and how to use graphs to represent information. I knew that, I know that, but I got so flustered when asked that I didn’t have the words to articulate it that well, so we’ll talk about it more tomorrow as a class. Tonight I’ll need to think up some other ideas that use similar representations that they may be more interested in, like income over time or money spent over time or data used on a phone contract.

Honors Physics: We went over some N3L problems, like one box pushing another, and the awesome part was when one student discovered the system method all on his own. That led into a great conversation where I showed them “the easy way”, but cautioned them that not all systems can be solved with it, so they still need to know the long way ’round. I think I’m pushing them to use system schema and draw FBD too early when questions could be answered without the full analysis. I may be over-selling the importance of the techniques when they haven’t seen problems that are hard enough yet to need them. I haven’t found the right balance between just-in-time skill introduction to give it context and giving them enough front-loaded information to feel comfortable with the skills by the time they really need to use them. We started to talk about the cart and hanging mass problem, and they named the cart Carl and the hanging mass Bob, which I found HILARIOUS. They had no idea they were naming it what it is. They also didn’t find it near as funny as I did when I told them it really was called a bob. Harrumph.

AP Physics: Ok. I learned a WHOLE LOT the first class that made the second class way very much better. I set up two labs so there could be multiple stations, but one of them was way short and the other was way complicated, so the balance was way super off. For the second class, I only had them do the complicated one, but in bigger groups, because it did take a lot of time and thinking about things and trying stuff. I also forgot to give the quiz to the second glass, so they had about 20 extra minutes the first class didn’t have. OOPS. I’ll fix that tomorrow.

The lab question: How does friction affect a system compared to the “ideal” acceleration?

The setup: A dynamic cart with a string over a pulley to another mass. They can add mass to the cart or to the end of the string. No, ROPE! I just read one of Kelly’s blogposts about how she only calls them ropes, because spring and string are too close and hard to hear the difference. Hard to hear, nothin’. I can never say the one I want to on the first try. So, from now on, springs and rope. Massless, thin rope, but still ROPE. Ha!

The goal: Anyway, the goal was for them to figure out what is the ideal acceleration with no friction and then fool with stuff to see what gave the biggest difference from the ideal situation we’ll talk about tomorrow. I hoped that this would make them care about analyzing the ideal situation tomorrow and comparing it to a bunch of different real scenarios. I have no idea how it will turn out, so we’ll see whether we can safely consider the dynamics carts to be frictionless and under what conditions. I’ve never actually looked at that before, especially with dynamic carts that I’m pretty sure are older than I am. I’ve said ‘assume no friction’ and left it at that, so I’m pretty excited to see the results tomorrow.

Duty Night: This duty night was a lot more quiet than last week. It did a really quick sweep at the beginning, a longer round with room inspections in the middle, and another quick sweep at the end to remind everyone not to start fooling around at 9:15 just because study time was ALMOST over. It goes until 9:30, so if you’re going to waste your own time, well, I will strongly suggest you reconsider, but at the very least don’t make it so that other people cannot study effectively. I asked one kid which class had the homework where he was supposed to do yo-yo tricks in the hall. He quickly changed tasks.

We have one kid whose room is always a disaster, so he’s failed inspection after inspection. I asked him what the obstacle was that kept him from cleaning his room. He said he kept forgetting. Ok, what can you do to help you remember? He suggested putting a sign on his door. Great! How about an alarm on your phone, too? He agreed. Then I made him clean his room. It was a lot easier for me to keep an 8×10 dorm room clean than it is for me now to keep a damn apartment clean, so I’m feeling less hypocritical than I did before. Context matters, and seriously dude it’s a tiny room. At the very least have a clear pathway to the door so you can walk in and out without tripping. I’m also feeling a little more grounded after three weeks of doing this and settling into the position as I understand my responsibilities and the intentions behind them.

The next step is to actually hand out consequences for infractions rather than warnings before I get the reputation for letting everything slide. I’m so bad at punishment, though! I don’t believe it works as a concept, so it’s hard to add to these kids’ already too full and super stressful schedules with assigned chores or grounding them to their room or to campus. I’ll figure out how to manage it somehow. It’ll just take some more time and thinking.