tag:lernerphysics.posthaven.com,2013:/posts Lerner Physics 2021-04-30T13:21:35Z Michael Lerner tag:lernerphysics.posthaven.com,2013:Post/1171996 2017-07-09T22:24:29Z 2017-07-09T22:24:29Z Standards-Based Grading in AP Physics C

I learned about standards-based grading from the best. This blog post is my take on how to do SBG in AP Physics C. My APC students took AP Physics 1 and AP Physics 2 as a double-period, year-long course as juniors. They're taking APC as seniors—first semester Mechanics, second semester Electricity & Magnetism. This class is about taking the models we learned with algebra and making them more powerful.

I use a scale of Mastery, Proficient, Approaching, and Beginning. Mastery is NOT perfection; the problems in AP Physics C are often too difficult for 97% of APC students to solve in such a short amount of time without talking to other students. I ask difficult questions that I don't expect students to get 100% right. Mastery means that the student understood the problem, used the correct model, and was on the right track. Most of the time, when I have the time, I have students check their own work and assess themselves against the standards. They are usually a little bit harsher than I would be, but I've learned to believe them when they say they deserve a "beginning."

My standards come from reading the AP Physics C Course Description. My standards are focused on the AP Exam even if my teaching isn't always focused. Here are my standards:

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1132450 2017-02-19T00:29:17Z 2017-02-19T00:29:17Z Brute-Forcing a Sphere as a Gaussian Surface

I'm not going to bury the lede. The blog post below describes my experience programming; a later post will explain how I'm going to use the program next year. The program shows the flux as brighter or dimmer shades of red (flux out of the surface) and blue (flux into the surface). Play with it. Zoom in and out. Rotate the sphere. Edit and break the program. (I tried to write a lot in the comments, so hopefully you can change a number or two and see what happens.) Give me suggestions. (My students like running it in fullscreen. Find that in the menu at the upper left of the screen.) Here you go:

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1090416 2016-09-15T16:28:43Z 2020-11-03T18:48:14Z Day 18: The SOS Diagram

So, after a day of learning that the slope of the momentum-time graph is the force, and another day when we figured out the area of the force-time graph gives you the change in the momentum, we were ready to put this model to use.

I know that lots of people use momentum bar charts, but I'm not 100% sold on them. I could be convinced, and I know that energy bar charts are A-MA-ZING. I wanted to play around with momentum bar charts that made the focus more on the motion of the objects and less on the blocks.

So, following in the footsteps of the LOL diagram, I use the SOS diagram. The name will make more sense a little later.

Remember, my students have done balanced forces yet. They only know that a force is a push or a pull and is the slope of the momentum-time graph. I start by introducing interaction diagrams.

First, we make our first interaction diagram together as a class. We use the setup in lab as our situation. (I took a picture of the setup and posted it at the beginning of this post.) We start by listing all the objects we care about and putting them in bubbles. Then we connect the objects that interact with lines. Usually, to interact with an object in a physics sense, that is, to put a force on it, you have to be touching it. There seems to be only one exception we have right now, and that would be the Earth. It seems to push everything around, even when we're not touching the Earth. I mean, that's why babies are FASCINATED by dropping objects from high chairs. "Look!" they seem to scream. "This object is being pushed around and NOTHING IS TOUCHING IT." We aren't usually as impressed nowadays that we're older, but we should be. Anyway, here's what the interaction diagram looks like:

At this point, what interaction or interactions are changing the motion of the object do we care about? Really only the spring on the cart. That's the one that changes the car's momentum. Wait! This diagram shows what changes a car's momentum! Cool! So I can draw the picture before that interaction and after that interaction and put a (simplified version of the) interaction diagram in the middle:

The first diagram represents pᵢ, the second diagram represents ∆p, and the third diagram represents the final momentum (there's no Unicode for subscript f. That makes me mad.)

So, we have our equation here, in picture form: Initial momentum + change in momentum = final momentum. Or, since change in momentum is the area of the force-time graph, and the simplest way to calculate that area would be a rectangle where the base was the time and the height was the average force for the situation, we can write it as...

Initial momentum + average force * change in time = Final momentum.

So why is it an SOS diagram? The O is for the system schema in the middle (which I call an interaction diagram, because 'system' is used differently by the AP, and I don't want to confuse my students), and the two S's are for sketch. It also is a cry for help when you're using the momentum model.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1090199 2016-09-14T23:27:32Z 2016-09-14T23:27:33Z Speed Group Hangs

I love Whiteboard Speed Dating. I love the cross-pollination of ideas that it requires. I really like how students have to deal with the whiteboard in front of them, the ideas of their partner, and their own ideas when they switch boards.

We were starting unbalanced forces, and it was time for those elevator problems. You know the ones—the elevator is going down at a constant velocity or the elevator is accelerating upwards at 2.5 m/s².

First, I told the students to get rearrange the tables and get into groups of three or four. I have them two minutes to move the furniture and get into their original groups. (I have a small class—only 14 students. I know, I know.) I think groups of three to five would work the best here. I wanted the groups to be big enough to have students who think in different ways and at different speeds.

Once they were in ready, I told them we were going to do something similar to speed dating. Instead of two people on this date, you're going to have three or four. It's not really a date, then, is it? It's more like a group hang.

You're going to start this next question as a group. Try to figure out how you'd approach it. Draw diagrams and do some math. Don't use whiteboards; just talk through your ideas and write them on your packet. But don't get too comfortable. Just like we we did speed dating, you're going switch. You'll get a whole new group.

So, while they were starting the problem of a person accelerating upwards on an elevator, I started giving each student a card with a number on it. I made sure that, in each group, every person got a different number. I listened in as each group came up with strategy, and noticed how each strategy was a little different.

Very quickly, before any group had really finished coming up with their strategy, I had everyone stand up. All the 1's go to this table now, all the 2's here, and so on. (You can see the all the 2's on one table in the picture above.)

When they got together, they had four different approaches to the problem. Each person in the group was an expert in a different way to solve the problem. Some were more elegant; some were clunky. At least one had a fatal flaw. But it didn't matter. They were expert in an idea that was the group's idea, and their job was to express that idea. The four groups then worked until they came up with an answer. All four groups quickly came to consensus.

I did this four or five times during an hour. It went great. I spent a little time asking for a class consensus about what the positive and negative signs mean in Newton's second law. But all the groups got to the same point at about the same time, and once the groups realized that everyone got the same answer, they felt really confident in their thinking.

This method fixes one of the drawbacks of speed dating. What if the students don't get along? Who decides if the two students have wildly different ideas about what to do next? Is just one person writing on the board? Now, everyone is writing on their own paper. And students can listen to opposing ideas and act like the judge. (I saw that happen more than once.) As one of my students said during this activity: "Speed dating is awkward. Speed group hangs are fun."

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1089389 2016-09-12T20:43:44Z 2016-09-12T20:43:44Z Day 16: Starting the Momentum Model

If you've been following me and read this tweet, you know that I'm going to be defining momentum in a different way this year. We're defining force as the slope of the momentum-time graph. This means we have to define momentum too, which is the hand-wavy part of this unit. Why even come up with this concept? Luckily, we define momentum as "how hard it is to stop something" and "mass times velocity" before anyone was too awake.

Then we went to lab and had a cart bounce off a force probe. We changed the mass of the cart and the spring on the force probe. We graphed momentum-time and force-time graphs. Here's what students noticed in lab:

• The momentum of the cart stayed constant except when it is touching the force probe.
• The force was negative because it pushed in the opposite direction of the initial motion of the cart.
• The momentum of the cart started positive and went negative.
• The force was the largest when the momentum of the cart was zero.
• When we used the springs, the momentum after hitting the spring was the opposite of the momentum before hitting the spring. The two momenta had the same magnitudes.
• When we used the clay, the momentum after hitting the spring was less than the momentum before hitting the spring.
• We could never get the final momentum to be larger than the initial momentum except that one time when the plunger exploded and hit the force probe, but we don't think that counts.
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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1088386 2016-09-11T00:40:40Z 2016-09-12T15:02:11Z Using Haiku for SBG

Giving good feedback takes time. And to read such a long post, you're going to need to gifs, memes, and screenshots. So let's improve this post.

Maybe you used to love ActiveGrade for Standards-Based Grading. (Or, like John Baunach, you're just starting SBG this year.) And now you're using Haiku Learning Solo Edition. It's OK, but you're not sure how to use it. I'm going to use this post to explain what I'm doing to make SBG work for me on Haiku. I don't feel like an expert at all, but I've bumbled my way to a workable solution for me. It may not work for you. I'd love to hear how you use Haiku as well, and I'll update this post (and give you credit) with your ideas. For example, I give credit to Kelly O'Shea who asked for more pictures and memes. Hopefully, in a year, I'll just delete this whole post and refer you to something better.

Until then, let's get started.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1085245 2016-08-30T20:15:09Z 2016-08-30T20:15:09Z Day 9: It's OK to be Wrong, but It's Better to be Confused

We had great discussions today about different situations where objects are accelerating. They were deep and interesting and in each class, students brought up some great ideas.

I took no pictures, though. I feel like a #teach180 rookie.

So, instead, I'm going to focus on how hard it is to be wrong. Students don't want to put up wrong answers. I had a student today who told me he was worried that other students would judge him for not understanding the material. I talk about how important it is to discuss different ideas. I train students to ask questions rather than just point out flaws.

But I feel like I'm still caught up in the right/wrong paradigm. I don't think I'm pushing the conversation from answer-finding (which is all about right and wrong) to meaning-making (which is all about clarity/connections and confusion/disconnections). I need to work on communicating that to students. Instead of, "what do you like or not like about these boards?" (which is my go-to question about whiteboards and is way too vague), I'm going to try other approaches. My ideas so far:

• What connections between the ideas on the board to you see? (Like, how do the position-time and the velocity-time graphs relate?)
• What connections do you see between this problem and the problem where...?
• What makes the most sense to you on this board?
• What did you learn by doing this question? (Or what did you learn from the discussion of this question?)

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1084864 2016-08-29T23:05:23Z 2016-08-29T23:05:23Z Day 8: What Students Think About When Using Motion Detectors for Carts Down Ramps

Here are the issues my students thought about when they used the motion detectors to look at carts speeding up and slowing down on ramps:

• Is the position-time graph for an object going down a ramp starting at rest an exponential or a parabola?
• How can the slope of the velocity-time graph be negative when all the velocities we measured were positive?
• So, when the velocity is negative, the acceleration is always negative, right?
• So, when the object is moving in the negative direction, the acceleration is always negative, right?
• So, if the object is slowing down, the acceleration is always negative, right?
• So, if the velocity is decreasing, the acceleration is always negative, right?
• So, if velocity is a slope and acceleration is a slope, they have the same shape, right?
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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1084185 2016-08-26T14:59:11Z 2016-08-26T14:59:11Z Day 7: What does the P mean in CVPM?

We took our first quiz today about CVPM. But our short lesson today was about the particle in constant velocity particle model.

Mr. Kaar, Mr. Engels, and Ms. Pollack, and I created a unit to explore what "particle" means in CVPM, and how it relates to conservations of quantities in systems. This lesson is the first part of this.

We start with a video of two air pucks connected by balsa wood sliding along the ground. We make sure we know what those air pucks are, and how they seem to move at CVPM. We then learn how to track one air puck. (See awesome gif above. Thanks, gifmaker.me!) Cool, a motion map! That motion map doesn't look like CVPM at all! We look at the position-time graph, and that doesn't look right either. It's way more complicated than a straight line. What should we track? Students usually quickly realize the middle is what we should track. We then do the same thing for three air pucks attached into an equilateral triangle. What should you track now? That's more difficult, because the middle isn't really part of anything. But it still works!

We then give them the two pucks again but this time, when they track the center, it doesn't look right. Why? Because we secretly filmed it on the ramp outside. So that's why the dots on that motion map aren't equally spaced. It seems to be speeding up, which is what we'd expect on a ramp. Guess we'll have to test things on ramps with the motion detectors on Monday...

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1084029 2016-08-25T19:53:16Z 2016-08-25T19:53:16Z Day 6: Speed Dating in CVPM

We did physics speed dating (see this blog post by Kelly O'Shea if you want to know more) to tackle the most complicated constant velocity representations we'll do. I have to be careful at this time of the year; I can spend a lot of time making sure their model of constant velocity is perfect, but I don't think it really matters for a few reasons:
• We will get a chance (literally in the next unit) to deepen our understanding of these representations.
• It takes a lot of effort to get the last bit of refining. Do I care what they do on motion maps with the last dot? Well, no, not really. If a student decides to draw the position-time graph one more second to what the arrow says will happen next, I'm OK with that. I'm sure other physics teachers have strong opinions about this, but I don't, and more importantly...
• I don't know what we'd get out of having the best constant velocity model. Constant velocity isn't the cornerstone of physics. The next model is. I don't care if there's a small mismatch between my model of constant velocity and theirs.

Still, even with this leeway, we still have some important discussions:

• Where does a position-time graph? Does it ﻿always﻿ start on the vertical axis? Does it ﻿always﻿ start with the first dot?
• What happens between one region of constant velocity and another region? How can the velocity change and no time pass?
• What do the numbers on the motion map diagram represent?

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/976337 2016-08-24T14:03:31Z 2021-04-30T13:21:35Z Power Words for AP Physics 1

So, it's Wednesday, and due to our schedule, I don't teach AP Physics 1 today. So, instead of a teach180 entry, I've decided I'll use this time to write about something I can't fit into a typical #teach180 post.

Here's a post I started in November, and never posted. I think it's worth posting, and I have some questions at the end:

At a professional development meeting last week, Dr. Lori Wilfong spoke about how to teach vocabulary effectively. As an AP Physics teacher, I didn't know if it would be helpful, but I played along. I went through a few exams, looking for the words that I thought would be most powerful for an AP Physics student. Dr. Wilfong separated vocabulary into three tiers, and I used those tiers to guide my thinking. I didn't include any tier one words, which only have one meaning and that they'll probably know before entering the class. And I only included the most important tier three words, those words that are the specialized vocabulary of the subject matter. I looked for mostly tier two words, words that take on different meanings depending on how they're being used. I think the list is very powerful, and I think that students who consciously tried to know and use these words correctly would be at a great advantage.

Here's my list:

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1083420 2016-08-23T15:05:53Z 2016-08-23T15:11:20Z Day 5: All Classes are Different (when they talk about CVPM)

I teach two sections of AP Physics 1. They're both in the morning. They both have the exact same number of kids. They both had the exact same amount of time to do a lab with motion detectors. As two classes, though, the vibe couldn't be different.

One period talked about all the different situations with the motion detector pretty quickly. All the students basically agreed, and the questions seemed mostly limited to questions about the conventions of the representations. (Do the axes have arrows on them? When do the arrows go on the dots in the motion map?) When I was done, I was uneasy that they had not yet made their intuitions explicit. So we made a class consensus focused around two questions: how we show the direction of motion and how we show if the object is moving fast or slow in these different representations.

The other period, when going over the different situations, got into it. Some students seemed to want to represent what they actually saw in lab, while others were more willing to idealize it (use their "physics goggles"). Students could reason between the representations and give arguments for their answers. Not all of them, though, saw the situation the same way. It got a little hot. All the answers they whiteboarded were reasoned and not intuited. Even if their reasoning was not the same reasoning I would use, it was consistent and intelligent. By the time we did the class consensus, which I felt I should do, partially because I did it in the previous class and partially because I wanted to make sure we all ended up in the same place, every student was articulate about how to answer the two questions. The arguments were productive, but a bit too critical.

When we moved on to the next activity with the second class, I knew it was time to pull out Kelly O'Shea's Fun-Time Super-Cool Mistake Game™. (That's not what she calls it, but that what I call it in my head.) The mistake game is great; I learn more every time I read Kelly's post. I'm introducing it here because students were passionate about their answers, which is good, but were phrasing everything in terms of "right" and "wrong." I contributed to that; they started to echo my language about what I like and don't like by exclusively talked about what they don't like, meaning what they thought the whiteboard got wrong. This is a trap I fall in all the time, and Kelly O'Shea's Fun-Time Super-Cool Mistake Game helps me get out of that trap. I need to shift the conversation to questions like "According to the motion map, where does your object start? How does your motion map show that?"

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1083216 2016-08-22T20:24:13Z 2016-08-22T20:24:14Z Day 4: What Students Talk About When They Use the Motion Detector

After just quickly introducing the four ways to represent constant velocity motion of a particle (see my last post), I sent the students out to try to walk various position-time graphs, and then use the computer to find the velocity-time graph, and then represent that motion as a motion map and as words.

Some questions my students were thinking about today:

• Is going towards the detector the positive direction or is going away from the detector the positive direction? (Student tries it.) Wait, really? Why is going away positive?
• Do I ignore that first bit where I'm not moving yet, or do I draw it on my velocity-time graph?
• Can I just call where I start x = 0? (As in, if I start where I normally start a little ways away from the detector and don't move, can't I call that point zero?)
• How does the velocity change in an instant? Doesn't it take time?
• How can I tell which way to draw the arrows on my motion map?
• How does the slope of the position-time graph relate to the velocity of the object? (One student came up with a great rule for this. I don't want to put his or her name in here because I didn't ask for permission, but every time I came back to that group, I always went back to that rule, naming it after the student who came up with it.)
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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1082510 2016-08-19T15:21:28Z 2018-01-15T17:30:08Z Day 3: Summer Work and Explaining the CVPM Model

What does summer work look like for AP Physics 1? I don't want them to start doing any physics, because they don't know how the class works yet. But summer work is a good way, I think, to have students check in with their math skills and see if they know some of the mathematical moves they'll use in the class. I've posted two pages from the seven pages of the summer work above. The other pages are about simple trigonometry and literal equations.

We whiteboarded this problems today. I was happy to see that classes were ready to ask each other questions, without putting all the questions through me.

After that, it was time to sketch out, quickly, CVPM (the Constant Velocity Particle Model). Many units in this class are about the four representations we use to describe them:

• Diagrams: I introduce the motion map by doing an example. Sometimes I'll talk about a car with a leaky fluid. Other times, I refer back to what students did in lab to measure the speed of the buggy. I don't spend too much time on it. I focus on doing one quick motion map, asking if students can tell where are walked faster/slower/stopped, when I was walking forward/backwards, and move on.
• Algebra: Another quick one. At this point, I don't want to show all the equations we could use. Some students, as soon as they see an equation, use that representation above all others. I understand why; they take years of classes in the math wing where the equation is the best representation. So I try to deemphasize it as much as possible. I ask students what equation they used in math class to solve questions about speed. Here, I usually hear s = d/t; at other schools, I've heard D = RT. I write down either. I ignore it for now. (Later, when we've developed a good equation for velocity, I'll add it to the notes here, but not yet. I'm just keeping this representation open as a possibility.)
• Words: What words will we use for to describe this motion. Starting point, velocity, fast/slow usually come up quickly. I often have to give an example until forward/backward comes out. I don't like forward/backward because in this model, points don't have a front. I will sometimes do an example where I walk both forwards and backwards from the left side to the right side of the room. My belly button does the same motion, even though one is forward and one is backward. So I tell them, since I'm mathematical, I prefer positive direction/negative direction.
• Graphs: We found from doing the buggy lab that graphs are a great way to show your results. So a straight line on the position-time graph means constant velocity. We then answer these two questions: What does the vertical intercept mean in this graph? What does the slope mean in this graph? They are very useful, and that fact allows me to reiterate how important graphs are to physicists.

I don't always teach these four representations in this order, but I wrote them in this order because it's how I remember to do all four. I use the acronym DAWG. It's very 1990s, but it works for me.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1082200 2016-08-18T15:16:29Z 2016-08-18T18:45:05Z Day 2: Group Buggy Lab

Students whiteboarded their results for the buggy lab, and it was a lot of small handwriting, long tables, and half-hearted conclusions. No one, in words of Brian Carpenter, was willing to bet me a burrito on their results. We did come up with a list of things we wanted to see in whiteboards in the future: large, legible handwriting, multiple trials, and visuals would be nice. On the way home last night, I was thinking what would happen if we lined up all the whiteboards together. That's where the picture came from today, with many students timing the buggy for 9 meters every meter. I didn't like how teacher-directed it was, but my students and I did like how convincing the results were:

I think it worked to convince many students that graphs would satisfy all of our desires for easy-to-understand, convincing, efficient whiteboards.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1082034 2016-08-17T22:05:53Z 2016-08-19T20:40:10Z Day 1: My Take on the Buggy Lab

So, last year I blogged my combined AP Physics 1 and 2 class. This year, I'm going to do a #teach180 blog for a AP Physics 1 class. I have a student teacher this year, so I don't know how many days of the teach180 I'll get done this year, but I do want to blog a bit this year.

Today was the first day, and I wanted to get right to the lab. So we started the buggy lab. If you don't know about the buggy lab, Kelly O'Shea has an amazing description. We listed our observations; we figured out we would measure time. I do a lot of this lesson like she does. Thanks, Kelly (as well as Brian Carpenter and Chas Deremer.)

But then, when they wanted to use metersticks, I told them I couldn't find them. All I could find was a long measuring tape. So we could only measure the position of the car on the measuring tape rather than the distance from the start line. I like this move. We start with position this way. I also don't quite set my students up to get position-time graphs on the first lab. I like to see what they get without much guidance. (Also a Brian & Chas move.) When they all whiteboard their information, and see what a graph can do, the class often agrees that graphs are the best way to see all the information quickly. I like the discussion that comes out of this confusion.

I also learned something about the question "Is the buggy moving at a constant speed?" Some student hear that as "Does the buggy do the same thing every time?" rather than "During one time down the track, does it stay at the same speed during that one trial?" I'm not sure how to avoid that confusion.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1029312 2016-04-08T18:58:46Z 2017-02-21T22:42:19Z Day 141: Finishing the Curriculum

We finished the curriculum! We have more practice to do, and tests, and other such stuff, but the end is in the sight.

We ended with a whimper, not a bang, by talking about neutrinos and half-lives and picking up those last little bits of what's left in modern physics.

As I look back at the first few blog posts, I notice I used to write a lot more each day. I was at the beginning of the marathon we call a school year and not at the end. I also don't want to give away too much. Not too other teachers, or my students this year, of course, but to future readers of this blog, future students who might look here and know everything. It's a silly reason; I see lots of great physics bloggers talk about their every move in class in detail, with answers. But I shy away from telling too much.

Writing this blog has been worthwhile to me. I'm trying to think about what I'll do next year to keep reflecting on and improving my teaching.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1028716 2016-04-07T21:58:08Z 2016-04-07T21:58:09Z Day 140: Special Relativity

We whiteboarded our last photon model of light questions, and the best part of today was the questions. That seems to be my new theme; their questions are so well-crafted and incisive that they should be celebrated. What are the different ways we can define intensity? Why can't an electron just absorb some of the energy of a photon?

And then we moved to special relativity, and the questions kept coming: How is this related to time travel? How much energy would it take to accelerate me to close to the speed of light? What does it mean that "that astronaut" traveled 0.5 seconds into the future?

Now they want to study a lot more special relativity.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1027648 2016-04-06T19:37:04Z 2016-04-06T19:37:05Z Day 139: E = mc²

It's more of me talking, and my students asking lots of questions. They love it. I don't really know another way.

The goal was to talk about the different conservation laws for nuclear reactions: number of nucleons, charge, mass-energy.

But it opened up so many other questions, including anti-matter, black holes, and dark matter. I tried my best to answer. The conversations were rich and interesting and the questions were great, but I was the sage on the stage.

I can't wait until they start reading about all these topics and start teaching me. I'll have to wait to the book project after the AP Exam.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1025897 2016-04-05T19:30:01Z 2016-04-05T19:30:02Z Day 138: We can see the atomic transitions!

We played around with various different gaseous atomic spectra. They are so interesting! Neon looks so red, and the sample marked "air" has so many different lines. We took some artful photos through our cameras, as shown above.

We didn't get quantitative with our observations; I wasn't sure if it was even going to work, but I think next year we can get quantitative. The lines are bright and easy to see, even through cheap diffraction gratings.

We are definitely finishing the year, and, just like last year, when we get to the end of the year, the questions about quantum mechanics are good. Quantum mechanics is weird. I try to explain, and I also try to postpone. I'm not a quantum mechanic!

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1025071 2016-04-04T19:56:50Z 2016-04-04T19:56:50Z Day 137: Atomic Spectra

So, I'm finding the end of the year coming, and I'm actually in a good place. We're going to finish early. We'll have lots of time to review.

I don't think I've ever had that thought before.

We talked about atomic emission spectra. Of course, I didn't have the tubes ready today (I'll have them tomorrow) so we didn't get to do a lab with it. Still, I could show pictures of the sun's spectrum and its dark lines.

We figured out how to model atomic transitions. The best question was about how this model is similar to and how it different from the model of the photoelectric effect. We talked a lot about the differences of the atoms and what happens to the electron.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1024034 2016-04-01T23:00:00Z 2016-04-02T22:39:00Z Day 136: de Broglie & Bohr & How much should I be modeling this?

Today was very teacher-centric. I don't know how I feel about this. For one, this is difficult stuff to conceptualize, and for me to be there, introducing parts of it here and there and letting them try some problems about it, works better. They have some pretty strong models on the electric force and on waves that we can build on. I also feel shakier about this unit, which I abbreviate PMAM (the particle model of all matter), than any other unit this year.

I know I could make it more modeling-friendly. I could give them results to experiments and have them come up with explanations. But what those experiments look like, and what makes the data seem real rather than just words on a sheet of paper, isn't clear to me yet.

It's okay that I'm not done with this unit. I can see the improvements I can make in previous years. It's not like this year isn't successful. The derivation of the Bohr atom went smoother this year than ever before. But there's still more to do to perfect my practice.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1022981 2016-03-31T20:04:47Z 2016-03-31T20:04:47Z Day 135: Finding Planck's Constant

We tried to find Planck's constant using LEDs. We got numbers in the ballpark, but they weren't great. I think I've learned how to make it work better next time.

It's very interesting to see groups work through variables and units for their equations. We still like using J and E interchangeably for energy. We still aren't exactly sure how to find the units of the slope. These are skills I must emphasize more next year.

Then we started talking about how much like particle photons really are? Like, do they have momentum? And, if they do, then do other particles, like the electron, have any wave properties?

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1022808 2016-03-30T23:00:00Z 2016-03-31T13:32:53Z Day 134: Atomic LOLs

We drew some atomic LOL diagrams after the long test on the wave model of light. Most of us like those diagrams, but there are a few who don't. I like the system with the photon going in and the electron coming out, even though we ARE keeping the energy of the electron in our system. I'll try to modify the LOL next year to make that more obvious.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1021727 2016-03-29T19:48:25Z 2016-03-29T19:48:25Z Day 133: The Photon

What can we explain with light as a ray, as a wave, and as a particle? Let's whiteboard!

So which one is light, really?

Now I get to blow their minds. None of these models works perfectly. We have to make a kludgy wave-particle hybrid called a photon.

It ends in tears.

But then I made it all better when I said we can energy bar charts (LOL diagrams!) to explain the photoelectric effect. I'll show some whiteboards for that tomorrow.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1021228 2016-03-28T23:30:08Z 2016-03-28T23:30:08Z Day 132: The Photoelectric Effect

I need to build a lab for this. But, when I don't have a lab, it always seems that PHeT is there. And I'd use the PHeT simulation for this every year just because it makes it so much easier to visualize.

I always start the photoelectric effect by talking about Einstein's Nobel Prize, and the papers he wrote in 1905. I misspoke today, thinking that Einstein's work on the specific heat of metals was published that year. It wasn't, but his work on Brownian motion was that year instead. That makes that year even more amazing in my opinion.

We then experimented with what changed about the current as we changed the intensity and the wavelength of the incident light. We also investigated what happens when we change the voltage applied across the gap. Our results seemed weird until we came up with the quantum hypothesis.

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Michael Lerner

Yes, we played more with diffraction gratings, and we saw great patterns by just using one white light source (see above for three enthusiastic students' pictures of the diffraction). We also played with an electric rotator and strobe light bought long before I ever taught at this school. It's fun to play with persistence of vision. And we did clean up the mess of the back of my room.

But, more importantly, we talked about academic honesty and standards-based grading. Academic honesty is becoming an issue at our school. Students are driven to do well, feel pressure to do well, and will often do almost anything to get a good grade. But, my students said, with my grading system, the focus was on understanding and not doing. I then asked them for help about how I should tweak the grading scale for AP Physics 1 next year, and, with their help, we came up with this outline:

There are four levels, and a student progresses through the levels sequentially.

Level 1: Earned if a student was in class and did the labs and participated in some way in going over the problems

Level 2: Earned by getting a "Quick Quiz" 100% correct. I'll write many versions over the summer. They're designed to be feedback, to see if a student understands the major ideas of the standard.

Level 3: Earned by doing well on a problem in the wild. I will no longer tell them a reassessment is "for this standard." The students must find a problem in the wild, on a longer assessment, and use that standard correctly, along with other ideas.

Level 4: Earned by showing mastery, either through particularly elegant solutions, using the idea over time, or solving difficult problems. This level is the least fleshed out at this point.

I also imagine you can't pass the class without earning at least level 1 on each standard and can't get above a D+ without earning at least level 2 on each standard. At least that's where I am now. Of course, any and all feedback is welcomed for this idea, which I remember seeing in some form on Matt Owen's blog.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1015566 2016-03-17T22:31:54Z 2016-03-17T22:31:54Z Day 130: Finally Getting to Burn Paper and Practice, Practice, Practice

We finally had a sunny day where the day wasn't packed with new material, so we went outside to use lenses and mirrors to focus parallel light rays to a focal point. And to burn things.

We then practiced doing single-slit, double-slit, and thin film questions. It was a low-key day.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1014870 2016-03-16T20:59:32Z 2016-03-16T20:59:33Z Day 129: A Small Air Gap Between Two Glass Plates

What causes the colors we see when we look at two plates of glass that are separated by a small air gap?

Before we could explain that, we had to talk about color. I wanted a short discussion about how we see color so we'd have some ability to say whether the colors of the two plates of glass looked more like rainbow colors or subtractive colors. We had so many questions about color. Color is so interesting, with tetrachromancy and bee vision being obvious tangents. We'd love to talk about it more, but I hurried everyone to looking at the plates of glass. So many students are gone Thursday and Friday for (another) robotics competition that I wanted to make sure all the new concepts were introduced today.

We saw the colors, and they were cool. They did not look like rainbow colors.

We then explained them by looking for a path length difference. But I didn't let them figure it out enough. Next year, I should make them do more of the thinking.

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Michael Lerner
tag:lernerphysics.posthaven.com,2013:Post/1014308 2016-03-15T22:17:38Z 2016-03-15T22:17:38Z Day 128: The Single Slit and the Pinhole

We started by working on lots of problems in class. I didn't give any homework at all last night. If we rush, we could finish the unit on Thursday, but why? Break is Friday, and if we take it slowly, we'll finish the unit on Friday and be ready to start the photon model of light refreshed after break. We'll need it; that model is weird.

We whiteboarded lots of diffraction grating and double slit questions, and it seemed that we were confused about when to use one equation and when another. It's a good idea to talk about the assumptions of each of the slit equations. The assumptions behind the slit equation are subtle, and I don't think I realized that until I was challenged so much this year. Thanks, class.

The last two questions we whiteboarded were about what we'd expect to see from one slit or from a small pinhole. We made predictions and then, of course, went to lab to see if we were right. We weren't. But when we talked about what was happening, it started to make sense.

Since so many students will be gone tomorrow, we'll learn the last part of the wave model tomorrow and then practice everything Thursday and Friday.

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Michael Lerner