Maglite. Shadow Puppet. Theatre

During my inquiry with maglites the other day, I came across a pattern of light that looked kind of like this by blocking out some of the light. The pattern of light was not quite so crisp and clean of course, and there were a few more details I’ve left out. Maglite shadow puppets can be bit strange, and this is certainly not the strangest.

I’ll try to get some photos up this week. But for now, the question is, “How would you make this? How do you know”

Pin Hole Theatre

I’m working through more of the SGSI roadmap. Today, I built a pinhole theater using a cardboard box, some duct tape, a white piece of paper, and aluminum foil. The box is big enough to put your head in, the duct tape is to block out all the light at the corners and seams of the box, and the aluminum foil is covering a hole I cut out, which makes it easy to create the pin hole and then change the pinhole size or shape. Across from the pinhole is taped a white piece of paper. When I stick my head in, I just use a sweatshirt to block out the light around my neck, and look at the white paper.

To me, pinhole theatres are more engaging and interactive than pinhole cameras, because it’s like a movie.As you move, what’s showing on the screen changes.

Here are questions that I think can arise in building one and taking it outside:

  • How does it work?
  • Why is the image “inverted”?
  • Why do we need a pinhole?
  • Why does the picture get blurry with bigger holes? What makes things blurry in general?
  • Why do other shapes (e.g., small triangle) work?


Other things can come up as well. For example, when shining light on the white paper in the theatre, you need a pinhole to show an “image” (technically not an image), BUT with a mirror, a mirror always shows an image without a pinhole. How is a mirror different from a white piece of paper? Doesn’t white reflect all light?

To make sense of these questions, new investigations arise. Including shining light through holes, down tubes, onto paper, shining multiple lights through holes, shining lights through multiple holes, eventually toward figuring out how light gets from sun to objects in the world, to the screen, to your eye, and what happens to the light at each stage.

So, we have mag-lites, then pin hole theatres driving our investigations, and then I think it’s onto eyes.



In my physical science course for future elementary school teachers, I am going to begin on the topic of light, which is where we will stay for about 4-5 weeks, following a lot of the notes and facilitators guides from SGSI.

I am amazed by how much inquiry you can do with a mag-lite. Probably on the second day of class, we are going to do a maglite dissection, which will our starting point for generating questions about how light works. Here is what a mag-lite looks like when you take it apart.

I’ll ask students to examine their maglites, fiddling with any adjustment to see what (if anything) they do. I’ll ask them to take it apart, looking at each the parts carefully, and making a diagram. I’ll ask them to label their diagrams, coming up with a name for each part and a conjecture about what each part is for.

Either during or after the dissection, I’ll ask them to take some notes on things they notice and questions that arise as they do a “maglite potato head”, using different configurations of the parts to see what effect they have on the pattern of light. For example, they might try out some of the following arrangements:

They can also hold the reflector over the shaft by hand and move it around. They can see what effect the cover has, or whatever else they want to try.

Through diagramming, whiteboarding, taking notes, and class discussion, I hope to make contact with some of the following questions:

  • What is the adjustor doing?
  • Why does the flashlight show a dark spot (in certain configurations)? When does it occur and not occur? Why?
  • Why are some areas of the light pattern bright than others?
  • Why does the pattern of light seem to show “rings”? Why do rings move when we adjust the reflector? Why do they move the way they do?
  • What does the reflector really do? How does it work?
  • What is the shape of the reflector? Why is reflector shaped the way this is?
  • What’s the best positioning of the reflector? Why?
Hopefully we’ll begin building models and establishing rules for light with some common goals in mind of explaining issues pertaining to the dark spot. Along the way, we’ll have to accomplish a lot, which will eventually necessitate us breaking into different research teams. As we develop various models and rules, there will be new predictions and observations to make progress, refine our ideas, and start to build support for certain models over others. Some of these include:
Reflector Effects
There are basically three regions of interest with the reflector that students will need to come to distinguish: When the bulb is near the focus of the parabolic reflector; when it’s below the focus, and when it’s above the focus.
Distance to Screen Effects
This is pretty complex, but it’s also interesting. For example, in certain configurations the dark spot in the middle is always present independent of the distance to the screen. In other configurations, the dark spot in the middle is there when far from a screen, but it disappears when you get close. Yet, in other configurations, there is no dark spot no matter where you are.
Effects of blacking out parts of the Cover
In certain configurations, blacking out the left half of the cover (e.g, with a permanent marker) will result in the left half of the light pattern being dark. In other configurations, no light is blacked out. Yet, it other configurations, blocking out the left half makes the right half go dark on the screen. Students can also block either the center of the lens or the edges of the lens, or a line through the center, and other interesting things happen.
Reflected Light vs. Direct Light (and patterns of lighter and darker regions)
Pretty soon, it becomes apparent that some light goes directly from bulb to screen, while other rays bounce off the reflector. Theoretically and experimentally, you work try to distinguish them, and this helps make progress with certain questions and ideas.
Shadow Puppets
It turns out that shadows act VERY different near and far from the light bulb, and they also act very different regions in concert with different configurations of the reflector. For example, in some configurations it’s almost impossible to block out the center with out basically blocking the whole flashlight out. Other configurations lead to an exaggeration of shadows near the center, making the shadows look bloated at the center; or contrary makes shadows shrink at the center. Other effects with shadows arise such that when you poke your finger in front of the flashlight, you produce not only one shadow but two.
Light on Plane and Curved Mirrors:
Of course, we’ll need to develop some rules about what happens when light becomes incident on mirror. For this, some groups will have to investigate this. Some might start by develop rules for plane mirrors.  Laser pointers and protractors can come in handy.
Of course, we won’t stay with maglites and darkspots forever. We’re going to want to move forward to pin hole theatres, explaining how those work, and building toward and understanding of blurriness, which may or may not lead us to studying lenses and the eye. Then, of course, we’ll move on to studying color. We’ll build spectroscopes, eventually take photos of spectrum, and use video tracker to analyze them, and start to build rules and models of color. I’m going to have them read some cases about color blindness and after effects. A big puzzle I eventually hope to make contact with is the issue of yellow, yellow, and yellow, and why magenta isn’t in the rainbow.
But right now, I’m pretty obsessed with maglites. Who thought that with a light bulb and a mirror you could investigate so much?

Life Lessons Continued

@ adchempages wrote to me on twitter that the life lessons he aims for students to learn are the following: Discipline, Punctuality, Politeness, Deadlines, Respect, and Accountability.  In this post, I elaborate on what those words mean to me.

Discipline: I interpret this as mostly involving self-discipline. To me, having discipline involves persistence with the work of moving toward one’s own goals, especially in face at adversity. It is not discipline to obey others or to fulfill the goals that others have for you.

Punctuality: I interpret this to mean to strive to act with conviction when needed, and to have one’s words be coherent as possible with one’s actions. It is not to be on time, but rather to be exact in one’s actions.

Politeness: I interpret politeness to be humble in the face of the unknown and unknowable. Politeness is the counterpart to punctuality.

Deadlines: I see this as the need to act in a timely way such that no one else is harmed by one’s inaction, especially those to which you hold community relation. The premise for this is that the choice not to act is an act.

Respect: To be receptive to possibility that you can learn from anyone and everyone and to act in ways to make learning interactions more probable and more fruitful.

Accountability: To be aware of one’s multiple and often conflicting responsibilities to self and others and to act in ways that are mindful of such conflicts. It is to treat community as part of self and self as part of community.

Why I’m against sig figs

I’ll confess that I’m strongly anti-sigfigs. My problem with sigfigs are the following:

I have never met a scientist or engineer who uses sigfig rules in their daily practice or in scientific communication. My understanding is that sigfigs are a staple of “school science”, in much the same way, “the scientific method” is. Based on my experience, sigfigs are typically used in a way as to mispresent scientific practice and thinking.

They are just rules to follow, which can be followed mindlessly. Perhaps, they are or were intended to cultivate habits for thinking about uncertainty and precision, but I have found that they almost always invoke authoritative non-sense from students.

– Thinking about spread in data and uncertainty in the determination of quantities does not require the complexity of std dev, nor the formalism of +/- notation, nor the mindless routines of sigfigs. For example, ranges can be talked about and represented graphically. I want to cultivate the thinking behind and along with the increasingly sophisticated routines we use, but only as they become relevant to the increasingly challenging practices we carry out.

– Most college professors (that I have met) who relentlessly deduct points for sigfigs also do not have meaningful criteria for evaluating the quality of student scientific work, practice, and thinking. The way I see it, many of these professors need some way of creating a spread in their grades and deductions like “sigfigs” and “units” are an easy out, which they can also defend on the basis that they reflect important scientific thinking. I’m not saying the thinking behind uncertainty or units isn’t important–I’m saying that  sigfigs is for a poor proxy of scientific thinking and habits of mind, and that relentless grading of sigfigs often comes as the expense of meaningful assessment and feedback.

Sigfigs are wholly un-generalizable, because they do not cultivate the right thinking or appreciation for their purpose. Students are left helpless when thinking about anything beyond the rules– for example what would such students do when they have uncertainty in an angle and they have to take the sine or cosine or tangent of that angle, or take the reciprocal of some quantity such as frequency and period.

As an added note, this post was inspired by this weel’s Global Physics Department for readers who aren’t aware. This Wednesday (8/10/11) we’ll be discussing various ways to teach error propagation.!/

This is the “corkboard” we’ve been using to brainstorm ahead of the meeting:

If not for others…

Here I remember those who nudged me along.

As I have written before, my road into teaching began in an Ameri-corps affiliated program called “Teach Baltimore”. In that program, I taught Kindergarten for two summers in West Baltimore at an elementary school called Steuart Hill. Mrs. Patterson was one of the Kindergarten teachers at Steuart Hill and she served as my mentor teacher. For me, commanding a classroom of six-year-olds was less difficult than it was for many others in the program, but Mrs Patterson never let me rest on that alone. She always challenged me to focus on student learning and on how my responses to their mistakes influenced that learning. At the end of the program, many of us were approached by the school system to become teachers (often in special ed) with out any certification or formal training in education! Mrs. Patterson encouraged us to not take those offers, and nudged us to enroll in graduate programs that would better prepare us to be teachers and teacher leaders.

In my senior year of college, I had decided I was going to go into teaching. That fall, however, I met Jo Ellen Roseman, who is the executive director of Project 2061 at AAAS.  She was my friend’s Aunt, and I actually met here at his graduation party. Jo Ellen talked to me about being a physics major and my interest in teaching. She convinced me that I should apply to graduate schools in physics and study physics education. I took her advice. Jo Ellen still on occasion sends me emails to check on how I am doing and submits my name here and there for things.

For graduate school, I ended up at Arizona State University. While I was there I did some curriculum development, got to hang around the modeling folks, and began carrying out investigation in physics education research. For a variety of reasons, things were not panning out there. Through my advisor, however, I had met Steve Kanim, a professor at New Mexico State University. As things were starting to deterioriate at ASU, I cold-called Steve and asked if I could come to NMSU for a few days and get some advice on some research I was working on. Steve said yes and Steve’s family let me stay at their house and fed me. Steve spent two or three days with me, discussing my work, pointing me to literature. In particular, Steve pointed me to some of the work written by David Hammer and Joe Redish.

That summer, I paid my way to the Summer National Meeting of the American Association of Physics Teachers. There I gave a talk on the work I had been discussing with Steve. For some reason, my computer wasn’t working, and I had to give my ten minute talk without any slides. Rachel Scherr, who was at my talk, approached me later that day about transferring to Maryland. I started at Maryland three weeks later, and that is where I finished my PhD in Physics Education under the guidance of Rachel Scherr and David Hammer.

I am very grateful to Mrs. Patterson, Jo Ellen, Steve, and Rachel for who they are and for their willingness to take me in and nudge me in productive directions. I can only hope to repay the favor by advocating for others in the way they advocated for me.

Assessment, Feedback, and Grading

This post marks my change from blogger to wordpress.

This year I have been introduced to range of assessment and/or grading systems that I will be or want to implement in various way:

Mandatory proficiencies:  With this, some subset of learning targets that are designated as “must-haves” before students are eligible to pass a course. For an example, see this post at Physics! Blog! The idea is that you as a teacher should be able to look someone in the face and say, “I can guarantee that every student who passed my class learned XYZ”, rather than say, “Well they knew 80% of the material” and be left not knowing which 80%. I like this because it makes you think hard about the “core” of your discipline and what you can expect from students.

A is for extra-ordinary: With this, excelling in normal classroom activities and their associated assessments can at best earn you a B. Successful completion of independent projects, investigations, or inquiries are the basis for B’s becoming A’s. For an example in math, see this post at Overthinking My Teaching. I think that Kelly’s synthesis method for A’s is a spin of this as well, see Physics! Blog! again. The idea is that B means students have learned well what you expected them to learn, and that an A has to be above and beyond.

Collaborative Development of Rubrics: With this, you are looking to engage students in the development of criteria for assessing quality in (their own) scientific practices. See for example, this lesson from Student Generated Scientific Inquiry. The idea is that if teachers just assess student work, then students will never understand how to assess knowledge, which is one of the primary-driving mechanism of science. It also makes grading more equitable and transparent. Andy does this with his collaborative oral assessments–getting students involved.

Student self-assessment as precursor to Teacher Professional Judgment: With this, you require that students self-assess before a teacher will assess, grade, or provide feedback on work. This usually guided by some rubric where students have to make the case for quality of their work or participation. The idea here is that I really want to be able to use my professional judgment as a teacher, but I don’t want that judgment to be hidden from students. Also, I want students to be in a position to advocate for themselves and show me quality work that I may have missed. My professional judgement doesn’t make me perfect, and I want students to prove me wrong.

All-or-None: With this, every assignment or standard is either accepted or rejected (although often times with possibility for revision). There are a lot of people doing SBG this way, but I am going with this system for just homework assignments. With this, I don’t have to agonize over whether some work partially meets some criteria or whether (and how much) partial credit to give. It either is or isn’t acceptable.

Show me you’ve learned it, when you learn it: This is also the basis of many SBG systems. Students can assess and re-assess on standards, and there are  few “high stakes” testing, if any at all.  The basis of this is that learning is non-linear and variable. Giving students high stakes tests all the time is like demanding your child learn to walk or say their first word on a particular day. Why would a teacher be so vain as to demand that everyone know something on a particular day and then not care at all whether a student learns that material well two days later. Giving students the autonomy to assess when they want comes with a degree of responsibility that I think many teachers are scared to give students.

Assessments with Voice: The idea here is that you want to hear your students explain things to get a better sense of what they know and how well they know it. Andy Rundquist is King on this, and this post has lots of links to his many posts.

Immediate Feedback: The idea here is that students get immediate feedback and immediate second takes–one way to do this on quizzes is by having student scratch off which answer they think is right. They can keep scratching, but lose points the more times they have to scratch! You can read about this system and where you can get scratch off papers over at  Joss Ives‘s blog. What I like about this is that assessment is tied to learning in the here-and now.

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