Have you ever looked at the gender discrepancies on those who score a 5 on the AP Physics 1 exam? It’s nearly a 3-1 ratio! AP scrapped all of the data in 2021, so probably not. I started analyzing this data around 2019/2020 and was pretty shocked. It got way worse when you looked by race

“Surely not MY students” I thought. “I’m a female teacher AND I’m super aware of the issues around female performance in the physics classroom”

I checked my data. The same patterns persist.

So I dug a little deeper. I knew that I had female students who were on or above the playing field of some of my male students. What was going on that it was so hard for my female students to earn 5’s?

BY THE WAY… this is NOT a physics problem nor is it a math problem. Check out the gaps on AP Physics C and AP Calc…. WAY smaller

What I realized was it was their performance on the multiple choice.

Then 2020 offered an incredible opportunity. I could test my hypothesis by pulling the national data when AP had no multiple choice on the exam.

Guess what happened? The gaps were reduced.

In my college experience the classes I recall learning the most were the ones where exams were not “gotchas” but opportunities to deepen our understanding of the material. I had one teacher give legit take-home exams. It was nice, but not exactly a learning opportunity.

The next professor did something different. He gave us twice as many problems as would be on the exam a week ahead. We got together as a group and worked all of the problems over the week. The exam was “open annotated textbook” and the questions were ever so slightly different from the originals. The course was Physics 470 – subatomic physics. It’s the class I learned the most in.

The third professor who did something similar orally read us the exam the week before. He would leave out important details or specifics. “You have a circuit that looks like this… you will need to find the potential across two of the nodes” I also learned a lot in that course.

Taking all of these things into consideration, I’ve really modified the way I approach unit exams in my class. After seeing success with this model it has become a model I use starting on unit one and continue to implement until the semester mark.

I give students the entire test the day before the test.

Simple! I take off the part of the question that says “determine the _______”.

What do I mean by that? Here’s an example problem:

Now let me make this clear: students are expected to stow away all electronic devices before we begin so there’s no photos or google searches. Additionally, students are only allowed to use whiteboards. No paper. Nothing leaves the room.

Here’s another example

At first students are probably more stressed. The questions could be ANYTHING! The only thing students CAN do is EVERYTHING I want them to do! They have to draw force diagrams! Make graphs! Write out expressions for sum of torque and sum of forces. They have to consider all of the possibilities. And this is exactly what they need.

And the results?

First and foremost, implementing this strategy did NOT cause a huge increase in scores. In fact, some students still did kind of awful. What it DID do, what move up the mid-group from an anxiety score to a score that matched their classroom performance. This was particularly noticeable for.. you guessed it… my female students. The pretest in this case was a sample of questions from the unit one progress check. Students answered these in “test mode”. The post test was the actual kinematics exam. Below are the results:

Of course then I had to find out if it stuck. So when we got to the momentum test in January, I ran the data again. This time, there was no intervention: no sneak peek. And guess what happened?

What’s interesting is the number of male students who actually saw a decrease in score. I have a number of theories on this one, part of which being that they generally performed well on the first exam and so did not have that push to improve over time.

Due to the results of these data I have continued to implement this practice. After all, the goal is to get students working the problem, not searching for an answer!

“Ms. R I feel smart today!”

That was an exclamation I received from a student that made my entire week. What gave this student so much confidence? Retrieve note-taking.

Here’s how retrieve note-taking works.

1. You lecture to the students as normal. Students have their full attention on you. No one is permitted to write.
2. You stop talking and let the kids start writing.

That’s pretty much it! But wait… we can make it more powerful

3. Let students discuss their notes together so they can fill in any of the gaps
4. Put the slides back up on the screen so students can fill any gaps that remain.

I did today’s retrieve-note taking with my lecture on curved mirror rules. The first time I did this I was really concerned about the extra time it took. However, I’ve learned that the right kind of extra time always pays off in the end, and this is a perfect example.

I break the lecture down into 3 parts, and I have a packet for students to follow along. The packet also reduces the cognitive load and allows students to feel at ease that they don’t have to remember EVERYTHING

Here’s page 1. I do these notes up on the smart board for the first round:

Note: my smartboard notes are NOT a carbon copy of the packet. See below

Next we do the rules for the concave mirror, and last we do the rules for a convex mirror.

Here’s where the magic happens. When students are left to retrieve the information and record it in their packets, they are immediately processing the information. They are asking each other clarifying questions, it’s AMAZING. And because they are working with the material right away, there’s not a lot of time to forget.

So where’s the big pay off? In the homework. Previously I would find myself going from group to group re-explaining how to do the ray diagramming. Using the retrieval method I no longer have to do this and I can work with just the few students who really need extra support! My students actually complete more work more quickly and with more confidence than had I lectured traditionally.

So why does this work?

Whenever we receive new information our brain tries to fit it in to what we already know. The more connections the brain can make, the stronger the new connection will be, and the better we will be able to retrieve that information later. Making connections also allows you to chunk information, similar to why phone numbers are written like 123-456-7890.

This retrieval exercise provides students four different encounters with the material: orally, visually, written and verbal.

1. First they get the material orally and visually as it’s presented on the slides.
2. Then they reproduce this material by drawing and writing
3. They are also discussing the information

By the time they are using and practicing, since they have engaged at such a high rate they are more than ready to go!

Did you like this? Read more about how I use retrieval practices in my classroom here!

We are finally here! Thank you to everyone who has embarked on this journey of reflection with me. If you missed the first few posts check out the introduction to the entire series here. This is part 3 of a 3 part series on momentum. You can read how I introduce the unit with impulse and check out some of the follow up activities I do before we move into collision.

Today we are going to talk about momentum conservation. I find that most novice-style teaching approaches look something like this:

• Momentum is conserved. That means initial = final
• Write an mv term for each object in the collision before and after the collision
• Solve for the unknown variable.
• An even more novice approach is to use MVP charts to help students organize the information.

I’ll start with this: I hate charts almost as much as I hate formula triangles. Why? Because if students exclusively use charts to exclusively calculate values with no other expectations the “learning” is “I multiply these boxes” and “I divide these boxes”. This is not demonstrating much of anything except that the student could probably play sudoku (I’m also not a fan). I do however incorporate the charts for those “easy wins” with my regular level students as an option…but only after we’ve done some of the heavy lifting first.

Say what you will about AP as a program, it has made my teaching more thoughtful and as a result, way better than before I taught AP.

Recall that in the early days of impulse, students were asked to sort of consider conservation without outright stating it. We now go through this process formally. I begin with the following prompts:

From here we collectively work our way to the final statement that -Dmv1 = Dmv2…. and THAT is conservation. It is a transfer of momentum from one object to another such that the total of the system remains constant.

At this point it’s all about application for my AP students. They get thrown into the lab for a few days so they can collect data for the various collision types and determine whether or not momentum was conserved. (Lab handout)

After the lab students are given one collision type they are responsible for in a board meeting. Rather than having a class conversation I let students circulate and provide written feedback. (The prompts for the boards are at the bottom of the image below, feedback prompts at the top)

Board meetings are always opportunities for students to check their work, collaborate, and ensure they can submit the best possible product. While I took the idea from here, I do make modifications depending on the activity because some students… no matter what… will never speak in a whole group setting, but they will offer written feedback. Some students (myself included!) freeze “on the spot” but when given time to reflect, have amazing things to offer! I think too often we create classrooms that are driven by extroversion but never take the time to consider what learning looks like for introverts, and write it off as “shyness” or “refusal to participate”. I also like to have students circulate when we have a significant amount of information on the boards, so it doesn’t lend itself to a traditional board meeting.

We do some conceptual practice (which has a bigger Force? a ball that bounces or one that lands?) and we discuss how we could know if there were an external impulse acting on the cars during a collision. I love using this graph from AP and asking students to determine if there is an external impulse

Oh! But let’s not forget all of the richness we learned earlier in the unit! I need to make sure to weave in the first half of our learning with this second half! I assign students what I call “special problems“. This problem set is a few problems that are neither perfectly elastic nor perfectly inelastic, but something in between or there’s an extra nuance added. For each problem I ask students to sketch the force vs time graphs, solve the question, and then answer an additional conceptual item about the problem.

When we review these problems here’s what I do: I randomly select 6 students to put up the graph or mathematical solution to each problem. Then I select 6 more students and their task is to either explain the answer on the board if they agree, or write a different solution on the board if they disagree. When there is a disagreement we open the floor to a class discussion about the two different answers to decide which is correct.

What about 2D Collisions?

2D isn’t really a major emphasis in APP1. We discuss it briefly in terms of the vector nature of momentum so momentum must be conserved in each direction

Regular Level Physics

EDIT 2/7/2024 – I have TOTALLY shifted this piece in regular level physics! Check out what I did this year here!

In my regular physics class have to scale back just a bit and shift my focus. I give students opportunities for “wins” so they can feel like they “understand” and then I start layering some of the more complex problem solving tasks.

We begin with a marble activity. Students use the grove between their desks and run collisions with marbles (kind of like a Newton’s Cradle). They are asked to record observations about the velocity, and therefore the momentum of the objects. After this activity we have the same conservation discussion as my regular students.

The other major difference between regular and AP is that I present and have students practice each of the collision types one day at a time. When I present these I will show them the chart method first, explaining that it is an option, but not my personal favorite.

I also explain WHY it’s not my favorite. The reason is that you have to remember the important physics idea in the MIDDLE of your work… that initial momentum is the same as final. If, however, they do it in the algebraic way, they start with the physics idea and then they can forget about it. I generally have a 50-50 split in my room who does which method. The other important part about how I teach this lesson is I want to make it super clear that we get all of the same numbers both ways. For this reason I will copy the chart over to the next slide and solve the same problem in the algebraic way

The collision lab is also different. I give students one lab at a time and students collect the data in pre-made tables. Since students need to determine initial AND final AND keep track of signage, there’s just a lot going on to also add the layer of “do this without a guide”. It’s not my finest moment, but, again, my students need some wins.

Problem Solving Skill Building

Another layer I add to momentum is that since the equation and relationships are simple, I introduce proportional reasoning with students (what happens if we double the mass, half the velocity, do both?). Many of my regular level students really struggle with thinking in this way (so does AP!) but I feel it’s important that they get some exposure to this. We talk about how you could choose to make up numbers and see what you get, but it’s also more efficient to shove the changes into the equation and see what comes out

I’ve also started incorporating more ranking task type items that are conceptual in our classroom practice to push their problem solving skills. I intro with the following

Students then solved tasks like the ones below in groups on whiteboards. Notice that the tasks chosen are ultimately fairly simple. I did the colliding carts first because it provided numbers and allowed students to calculate in order to come to a conclusion

However in this final problem we did, there are nearly no numbers at all! This was a good place to really discuss the relationships within momentum, and in this case focus on what is the same, greater and less in order to come up with an answer. Student groups ended up being highly successful. We did about 4 of these tasks in the 50 minute class period.

I suppose I should discuss what assessments look like in my classroom at some point, especially for the non-AP students. Another day, another post! (Spoiler: it’s changed quite a bit since I first started teaching!)

Unit Summary and Shifts

In a nutshell, this is what my momentum unit looks like:

1. Discover impulse
2. Work quantitatively with impulse
3. Multiple representations
4. Using impulse to define conservation

Teaching Momentum, an Introduction

A quick review of my teaching values before we begin. See the introduction for more.

1. Any student can learn physics, and curiosity about the physics world around us is an innate attribute of humanity.
2. Intuition can be a powerful tool to co-construct knowledge
3. Order matters. Language matters. 
4. Shut Up and Listen
5. EVERYTHING is an opportunity for an experiment
6. My primary responsibility is to ensure a safe space for students to learn 

When I was taught momentum it looked something like this:

1. define momentum as mass x velocity.
2. Talk about how to change momentum through impulse
3. Revisit action-reaction pairs. Throw an egg into a bedsheet.
4. Define conservation of momentum as initial = final. Solve collision problems accordingly.

In my experience there was also no mention or use of various graphs. When I started teaching I was able to get a hold of the entire curricular materials from a prestigious, high achieving, highly affluent school in the area. They taught the sequence very much the same way. Obviously this was the “best” way to teach momentum… right? 

Over the years through a combination of teaching the AP curriculum, exposure to the ISLE method of learning and the modeling curriculum, this sequence has shifted dramatically. I have aligned many of my routines with these two models. However, my structure for teaching momentum is not the same order as ISLE or modeling. In both of those curricula, students are first tasked with discovering conservation through a series of experiments to kick off the unit. My order is slightly different.

One of the critical choices I make about momentum is to teach it before energy and after forces. I do this because change in momentum is a natural consequence of an object experiencing a force. Momentum is really just forces repackaged! I don’t want students to discover conservation first, because I want them to think about the processes during the collision first, then we can apply those to different scenarios. 

I was super excited to find out recently this has actually been studied. You can read the article here, but here’s the Tl;Dr –when students are taught from big idea down, they learn the material better, making more connections, and this study was specifically done with a framework for momentum. (See the framework below)

Momentum is a huge, critical unit, so I’m going to break this down into three separate posts. This first one will take a look at impulse. The second post will be a short explanation of two activities I do, one for regular students and one for AP. The last post will discuss conservation. I want to note that I do not plan on including every detail, activity and problem set in these posts, only the ones I think have substantial value to you, the reader, and those that constitute major shifts in my teaching over time. 

One thing that remained true, even in the very first years of teaching was my attempts at emphasizing that momentum is not something new, it is simply forces repackaged. The other statement I would make often is that the impulse-change in momentum relationship is two ways of saying the same thing. Like “Hi” and “Hello.” Yet, these ideas were not sticking in students minds. Furthermore, I was fully aware that students were making no connections between impulse and conservation. How do we get students to understand these ideas with full integrity?

The realization for me came after a vocabulary shift: rather than defining a force as a push or pul we now explicitly define a force as an interaction between objects. This definition became the driving force for my reframing of momentum. 

Classroom Activities

Please don’t steal for profit on TPT. That harms the teachers who share, those who are in need, and our profession as a whole.

Observational Experiment: We begin with an old demonstration from earlier in the year: our lovely bowling ball friend. We are already familiar with the fact that an unbalanced force will cause the ball to accelerate from the forces unit. I ask a student to give the bowling ball the hardest whack they can with a hammer. Unsurprisingly, the ball barely moves. But the force was so strong! What can we do instead? Well, if we tap the ball repeatedly, then it will begin to accelerate. This is how we first define the impulse-change in momentum relationship. We need a force exerted for a certain amount of time in order to change an object’s velocity. We do not define this yet as a formal equation, but we recognize that force and time must be multiplied. To define momentum itself I do a live google news search for the word momentum. The headlines are always sports, politics and stocks. We talk about what the word means in those contexts. We typically arrive at something like “having a lot of momentum means hard to stop” and then we formally define it as mass times velocity. I’ve never been one to do elaborate day plus activities to define simple terms when we can use their lay knowledge as a foundation for their scientific definitions. At least for something like this. We have much more important work I’d rather spend that precious time on. This is important as we move to the next phase. My students hear from me frequently: whenever you get a graph your first question should be does the slope tell me anything (division) does the area tell me anything (multiplication). 

Quantitative Experiment: I have run this lab two ways, but the idea is the same: have students quantitatively compare impulse and momentum change. The original way I performed this lab was to affix a force probe to the track, then run a car into it with the pistton out. The piston allows the time frame of impact to extend so students can see the curve. A motion sensor is set up on the opposite end so students can obtain velocity values. When we open class I have sketches of the graphs they will see and I asked them how they could determine impulse and momentum change from the graphs. Students are asked to sketch the graphs, determine the change in momentum and determine the impulse by using the software to take the area under the curve. In a newer iteration of this activity I use the iOLab to the same effect. Students run the iOLab into a wall or textbook and analyze the same data. I ask students to determine the relationship between impulse and momentum change. Then I ask them to write that relationship down and rearrange the equation until they get something they recognize. 

Recap and Multiple Representations – We will recap yesterdays activity through a discussion and whiteboard presentations. By the time we finish students recognize that the impulse-momentum relationship is just F = ma rearranged. This is where I emphasize again we are not really doing anything new. The next thing I ask them to do is to imagine the force probe/wall (depending on the iteration of the lab) was replaced with a second car of equal mass…what would the force graphs look like for each car? We are, in effect, previewing the law of conservation. If we go back to the definition of force: a force is an interaction between objects, then it follows that the force on object 1 must be equal and opposite to the force on object 2. The time must be the same. Therefore, the impulse is equal and opposite. While we could easily jump into conservation laws from here, we continue working with representations focusing on impulse and momentum change. 

In a whiteboarding exercise I provide students with several scenarios. In each scenario I have provided one representation. Students are asked to create the other 4 representations. The purpose of this is to ensure they are accessing everything they have learned already. This is, in some ways, I type of interleaved practice since they are pulling from the whole year.

One Final Problem Solving Example  

Over the next few days we continue our practice with an emphasis on multiple representations, graphing and the fact that an impulse causes a momentum change and that they are one and the same. One of my favorite questions is the following one. 

Identical forces push two different pucks the same distance. Puck A has four times the mass of puck B. Which experiences the greater change in momentum?

Can you describe what student responses look like? They come in three levels. 

Level 1: Puck A will have the greater change in momentum because it is bigger. More mass means more momentum. These students have missed the point completely. They are focusing on formulas and completely disregarded the velocity piece. While “puck A” is the correct answer, I cannot give credit for this response. 

Level 2: These students make some attempt to determine the velocity but end up writing a lot of circular statements and attempting a lot of calculations. Some of them get there, but this process is long and arduous! 

Level 3: These students correctly recognize that since impulse and momentum change are the same thing, they can easily look at the impulse to determine the answer. The force is the same, but the mass is different, resulting in puk A taking longer to get to the finish line, therefore puck A is greatest. 

I LOVE this problem so much. It’s a fantastic example of why expert-level thinking is so important for students learning physics. Students see the word “momentum” and they want to do p=mv. While you could do this, it takes a long time to get to the answer. If, instead, you take a step back and recall that impulse and change in momentum are the same, you see that you only have to figure out what is going on with time, since the force is the same. This piece is a lot more intuitive than determining the final velocities of each puck. I have used this as a warm up and as a quiz item. 

We also take advantage of the AP question bank and we will begin probing the idea of what it means for an impulse to be external vs internal. This falls in line with previous experiences related to defining forces and systems and serves as a good launch point for conservation of momentum.

Scaling Up and Down

Regular physics generally gets all of the same structure materials as AP minus the AP practice FRQs. I will, however, spend a little less time on multiple representations and a little more time on calculations for the sake of “easy wins” so students can gain some confidence.

AP Physics C: My students in this course have all taken APP1. We instead have a “momentum mastery” project, a quick 2D lab and AP FRQ practice.

One positive aspect of working with other teachers nationwide is you are forced to think carefully and critically about precisely what you do and why. Arguably we are supposed to be doing this as part of our daily practices, but too often we get so lost in the day to day we lose sight of the art.

It is my hope in this next series of posts to reflect and share on how I (currently) teach various topics in physics, and how that has shifted from how I used to teach those ideas. Before we begin on this journey together, it is important to lay out my values and beliefs around teaching this course.

1. Any student can learn physics, and curiosity about the physics world around us is an innate attribute of humanity. Look at any group of people from across the globe and you will find scientific curiosity and thinking. You will find ingenuity and creativity. Humans are constantly looking to explain nature and then use what is available to us to create, build and explore. This innate curiosity isn’t limited to rich, white men, it is literally a piece of our very humanity.
2. Intuition can be a powerful tool to co-construct knowledge: I was educated in a physics room where we regularly engaged in what Eugina Etkina calls “expose and shame”. Students are given a scenario with no prior knowledge and asked to guess the outcome. The outcome is always the opposite of what students expect. The unexpected is supposed to “stick” in students minds. Not only does the result not stick in students minds, this creates a classroom culture where students avoid taking risks and making mistakes. What I’ve learned from the modeling curriculum and the ISLE method is that we can help set up specific experiments and demonstrations where we first let student intuition help construct an understanding about an idea. As that idea becomes more solidified we can begin to introduce scenarios where student intuition may not have previously led them to the correct answer, but they can get there using the knowledge they have built in the course.
3. Order matters. Language matters. This idea is one that I have finally begun to fine-tune and refine just over the last few years. All of mechanics really comes down to 2 ideas: forces or conservation. When we boil physics down to the “big ideas” we can see what is truly important. The challenge, however, is that students tend to work in a very granular manner. They like to do things a particular way each time (algorithmic thinking) and they like to go equation hunting, thinking that thee “plug and chug” part of the problem is “the work” rather than all of the work that comes before the work. As a teacher I have two roles here: emphasize and make clear the big picture, and make all of the work before the work visible to my students. These ideas have shifted how I first present material to my students as well as where the emphasis lies within the classroom.
4. Shut Up and Listen: Not them… YOU! Getting out of student conversations and letting them run the room is a big challenge. Actually listening really carefully to the conversations happening in the room is another challenge entirely. I cannot count the number of time’s I’ve wanted to bring everyone back in after a time limit, only to realize groups were just getting to the good stuff in their conversations. So much of their learning happens while engaging in conversation, so we need to the make space for it.
5. EVERYTHING is an opportunity for an experiment: I learned this after working with Eugina Etkina’s ISLE curriculum and workshop and it finally solidified what I always believed to be true but struggled to put in a concrete way. I’ve never been one for showmanship, and I started my career around a lot of physics showmen. When I was in college it was the big “learn through inquiry” push, which was a step in the right direction but lacked structure. When I student taught I was supposed to do a day of thermo demos, but instead I turned it into stations. This is one part of my teaching style that has only grown over the years. “Demonstrations” are and should always be treated as observational experiments. If we want to treat our students as aspiring scientists, we should model our classroom on the scientific research structure.
6. My primary responsibility is to ensure students learn. This can only be achieved if a certain culture exists in my classroom. My room must be a place that is culturally relevant and responsive. It must be a place where students can take risks, ask questions and be heard. It must be a place where failure is part of the process, but never the end result. Where students know I care about their well-being and mental health as much as “finishing” the content by the end of the year. My classroom must be a place where the grade students earn is a reflection of what they have accomplished and learned in a semester, not an average of mistakes and compliance. These norms are achieved in many different ways within and outside of the actual curriculum.

I imagine I will add to the list as I start formalizing my thoughts around how I teach each of the units and build my classroom culture. One of the beautiful parts of blogging is actually taking the time to reflect on practices and receive feedback!