Talking PER to Physicists: An Experiment of My Own

I’ll be giving a talk to a Physics Department in a few weeks. So far, I’ve only had opportunity to do this once before, and it was around dissertation time. So obviously, I talked about my dissertation work. Now, I’m reaching a point where I think a lot more about how to engage different audiences with PER as a field, rather than just how to showcase my own work.

Anyway, here is a draft of the title and abstract for the talk I’ve been working on. Once the talk is done, I’ll come back and post.

Physics Education Research for the Physicist: Scattering Experiments, Model Building, and Complex Systems

Physicists and physics education researchers naturally study different phenomena. The physicist aims to understand the structure and mechanisms underlying physical phenomena, while the physics education researcher aims to understand the structure and mechanisms underlying particular kinds of cultural phenomena–that of how people come to learn and participate in the discipline of physics itself. Although the focus of their research is different, the two disciplines often employ similar methods, including experimentation, model-building, and theory development. In this talk, I frame several strands of research in physics education in terms of complimentary approaches in physics in order to answer questions like, “How is the FCI like a detector in a scattering experiment?” and  “Are there laws of student thinking that can actually predict what will happen in your classroom?”, and “How is inter-disciplinarity changing the research landscape in physics and physics education?”

Initial Moon Ideas

First day of the moon, I had students interview their partner about what reasons they can give for why the moon is sometimes only partially visible (or even not visible at all)? They were supposed to *not discuss their ideas* but act as a journalist, reporter–asking follow up questions, and taking notes to really get inside that person’s understanding. They then had to report out that person’s ideas to the rest of their group.

Students could then discuss and collaborate, and then white-boarded initial models. We then presented as a class. Here are my interpretations of ideas that came up.

Earth blocks Sunlight from Getting to Moon, casting a shadow on moon:

Version #1 (Moon configuration only):   New moon is when moon is behind earth receiving no light. Full moon is when moon is 180 degrees there, now getting the sun’s full light. Phases are when moon is in intermediate locations between behind earth and in front of the earth.

Version #2 (Moon configuration plus vantage point):  New moon is when moon is behind earth receiving no light from the sun, but a visible moon is anytime the moon is not in the earth’s shadow–what exact phase you see the moon in depends on your vantage point from the earth. For example, this group drew a “full moon” when moon just came out of the shadow. Then, whether you see  it as a full moon or another partially lit phase, depends on your location on earth.

Version #3 (Visible portion of lit portion):  New moon is when moon is behind earth receiving no light, therefore not visible. Solar eclipse is when moon is directly between earth and the sun, because moon is blocking sunlight from getting to earth. First quarter and 3rd quarter, are the result of the moon being at 90 degrees. Half of the moon toward the sun is lit, but only half of that half is visible from earth, making a quarter moon appearance. Crescents are caused when moon is just passing into the back of the earth (partially in the shadow), and this partial blocking effects that you might still only be able to see a part of the part that is visible (i.e., making less than a quarter).

Notes from presenting group: Full moon seems impossible to create, and so they are concerned that this mostly wrong. They also worry that their diagram suggests that a solar eclipse would happen all the time, and they know its more rare than that. They are also wondering about what is a lunar eclipse, and how that fits in.

Earth Doesn’t Block the Light to the Moon:

New moon is when moon is between earth and sun, because the lit part of the moon is facing the sun, not the earth, making it not visible to us. Full moon is when moon is on backside of the earth, where the lit side is facing the earth. This means that light must still get the moon somehow even when its behind the earth; so either light gets around the earth (due to its spherical nature, not wall-like nature) or the moon-earth-sun must not fall in a perfect line. This group actually began making a whiteboard the same as the group presenting version #1, but as they drew and discussed it they realized many of the same issues that group #3 discussed.

Other Commentary

As a class, we have very vague ideas about what causes configurations of earth-moon-sun to change–as some combination of earth’s rotation, earth revolution around sun, and moon revolution around earth. People seemed uncommitted and confused about what does what, and even confused about seasonal changes vs. lunar changes. We also have very vague ideas about the path of moon through sky, which is of course related to the confusion above.

Tomorrow we dive into our moon observations we’ve been collecting over the last 6 weeks, and working to put all our individual observations into a class-wide set of observations. Then I’m hoping we’ll do some work talking on issues of scale, and then revisiting our theories.

Experiments in Trying to Review and Move on at Same Time

One of the things I’m doing this year is trying to provide more opportunities for deliberate practice (with feedback), while trying to support students in building and articulating explicit strategies for solving problems (not me just telling them strategies), and selecting class problems to work on that can be solved with current ideas but also put us in contact with puzzles that later ideas will help to resolve or bring insight into.

Here is an example from earlier this week:

This week my students are going to be evaluated (by another instructor) on their understanding of projectile motion and Newton’s laws (including circular motion).* Afterwards, we are going to be diving into energy. So, how do I give them more deliberate practice and feedback with projectile motion and forces while also putting us in contact with energy puzzles? Here is what I tried:

First, I asked students to predict which of two ramps would result in a block of ice having more speed at the bottom. Both ramps were from same height, but one was shallow one is quite steep. No numbers were given. They think and vote peer instruction style. We were pretty much evenly split between all possibilities, so they discuss in small groups and then I collect arguments at the front board. The arguments were basically the following:

  • The steeper ramp has a greater acceleration, so it will be faster.
  • The shallow ramp will provide more time for the ball to speed up, so it will be faster.
  • The opposite effects of acceleration and time will balance out so that they take the same speed.

We’ve gotten pretty good at doing this, so I can mostly stand to the side and just write down arguments and do some re-voicing. After hearing the arguments, I have them revote. There were some shifts, but still not near any consensus.

I now tell them that I want to help settle this by applying some of the skills we’ve learned over the past couple of weeks. I add some information to the scenario. Block of ice has a mass of 25 kg. The ramps are angled 30 degrees and 60 degrees. The height is 5m. I split the class in half, half the groups work the 30 degree problem while the others work the 60 degree problem.

Before sending them off to work the problem, however, I tell them to talk strategy with their group–what will you need to figure out to answer the question, what skills and ideas might be useful, what might you do first, second, etc? They talk for a minute or two, and then we collect strategy ideas at the board. They say most of the things they need to–drawing free body diagrams, using Newton’s laws to find acceleration, finding the length of the ramp using trig, using kinematics ideas / equations to determine the final velocity, etc. Now they are off, and the board is there to help remind them of things they can try if they get stuck.

Doing this together makes me free to monitor for progress rather than helping students get started. I’m checking free-body diagrams for bizarre combinations of Normal and Weight fores, if and how they are finding components, whether they are using a rotated coordinate system and using that consistently with forces and kinematics, etc. I point out things that they are doing which are very “physics-y”, like drawing careful diagrams with labels, starting from big ideas rather than launching into equations, etc. If groups finish early, I ask them to solve for other things that came up in our arguments. For example, I might ask students to solve for the time on the ramp to see if its true that the larger acceleration was paired with less time to accelerate, etc. As multiple groups finish, I have them check with each other on their answer and check with people across the room.

Once we are done, I do a quick summary of what we found, highlighting that its odd that both ramps end up giving the block the same speed. I restate the arguments we heard, and I emphasize that the argument for the right answer made it seem plausible that it could balance out, but why it exactly balances out seems like a puzzle to me. It didn’t just balance somewhat, it balanced out exactly.

I tell them that I want to consider another problem where we compare final speeds, but this time not with ramps. In this problem a baseball player throws a ball with same speed. In one case the ball is angled upward, and in the other case the ball is angled downward. The question is about the speed’s of the two ball’s just before impact, and how will they compare. Students vote. This time there is a split between two answers. Most students vote they will be the same, but don’t have good arguments. They are banking on it being similar to the last problem. Intuitively, it makes sense that the one thrown down will have more speed, and I support this argument a bit. If you are throwing it down, in the same direction of gravity, and its got a real direct path to the ground, isn’t it going to be a lot faster when it hits. There are some other really awesome arguments for why it should be the same, about why it must balance out, including consideration of what the one that goes up is like once its on the way back down. The best argument came from a student who had never spoke up in large discussion, so I spent some time re-voicing that argument and giving it space for consideration.

Once again, I turn the conceptual question into two problems to solve, adding angles and heights and an initial speed. We talk and collect strategy at the board. They solve the problems. I monitor progress, give extension questions, ask them to check with each other. Finally, I summarize and make connections at the end. I still try to keep the puzzle open: Why is it that when the two blocks fell through same distance, and ball’s fell through same distance that their final speeds were the same? Our current skills help us to calculate that this is the result that should happen, but it doesn’t help to explain why.

An interesting outcome of asking students questions to compare, and then asking them to compare pairs of questions, is that they start doing more and more comparing. Several groups started re-thinking the shooter-dropper experiments. Looking for connections across phenomena is something I want to promote and this kind of activity seems to promote more of it.

Anyway. So later this week, we’ll revisit these same two problems from an energy perspective, but I’ll also introduce puzzles for us to resolve that further our understanding of energy and kinematics. Namely, this time we’ll do a problem where two balls rolls down the same ramp, one with an initial speed and one from rest. In this case, they will neither end with same speed nor gain the same amount of speed. Rather they will gain the same amount of kinetic energy…


* This used to bother me, having someone else test my students. But I now love it. My relationship with students is not of evaluator or judge. I am a learning coach. Sure, some of the evaluation is not meaningful. Sure, my students are learning things that aren’t evaluated. But my students do well on the evaluations for the most part, and students are constantly getting feedback from me on a broad range of their learning.

Reflection on a Day of Struggle

Teaching circular motion is just awful. That is, it is awful if you haven’t built a foundation of kinematics rooted in vectors quantities. How can you possibly interpret a centripetal acceleration of 4 m/s/s? What does that 4 mean?

Today is the first day all semester I’ve had to say to my students, “This makes no sense and right now we have no tools for making sense of it.”


Brain Dump…

Some Common Ideas I Hear and Some Evidence to Support Them

When you shine “white” light on non-reflective colored surfaces, the light that comes off carries or takes on the color of those surfaces. That colored light goes off in many directions (not just one).

When a flashlight was aimed at a colored piece of construction paper, pieces of white paper and even our hands that were nearby would be illuminated with colored light”

Colors from objects outside get inside box theatre to not only form an image, but a colored image that matches the color of the objects.

The color that objects appear to be in sunlight (or artificial light engineered to be similar to sunlight) is what we typically call “the color of an object”. The perceived color of an object can vary from its “natural” color if the light is colored light.

When we shined red light on the rainbow fabric, we saw a dark band and a red band. In white light, what was the dark band was now green, blue, and purple. What was the red band was now red, yellow, and orange.

When we shined red light on the yellow jacket and the white wall, the perceived color was indistinguishable.

Sunlight seems to consist of many different colored light (ROYGBV), and artificial light made to be similar to light is made of many different colored light as well.

When sunlight passes through a prism, the colors can be seen separately

When sunlight shines on a CD, the color can be seen separately

When sunlight passes through water the right way, it can creates a rainbow that shows the colors separately

When an i-phone screen is examined under a microscope, white light is made up of tiny reds, greens, and blues.

Questions I’ve heard come up

Does light absorb color from surfaces, or is light absorbed by colored surfaces?

What is the ontology of color? Is color a property of objects, a property of light, or both? Or is color just a physiological / psychological response to light entering our eye and our brain interpreting it?

Is the color of an object determined by the colors that reflect off it, or determined by the colors that are absorbed into it?

Is black all of the colors or the absence of colors? Is white all of the colors or the absence of colors?

If surfaces absorb some colors and reflect others, how does the object “know” which ones to reflect and which ones to absorb? What’s the mechanism?

How is mixing paint and mixing light similar / different?

Is every image (including color images) made of up tiny glowing dots /pixels, even if they are too tiny for us to see?

What is grey? What is brown? (If the color of an object really is the rainbow colors that are not absorbed, how can these be made since gray and brown aren’t in the rainbow?)

In what ways are sunlight and artificial light similar / different?

Why is yellow on the computer screen made up of green and red dots?

How does our eye perceive color? What is color-blindness? What does world look like to color blind people?

How do animals have night vision? Can they see in pitch dark, or just see well even in really dim light? How does night vision technology work?

What are primary colors? Why doesn’t a computer use red, yellow, and blue?

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