One of the powerful ideas we’ve had in inquiry class this semester is called “Amy’s Pee Theory”. It’s an idea we’ve returned to again and again in explaining phenomena. Amy’s pee theory states that if you pee a normal size amount in a very large pool, no one will notice. The pee (to be sure) is still there, but it’s been spread out over such a large thing, that it’s not concentrated enough to have a noticeable effect. Peeing in a smaller container of water, such as a toilet, results in a more obvious effect (yellow color), because the pee is concentrated in a small container. This idea is our class’s instantiation of beginning to think about a thermal reservoir.
Last week, our class discussed the energy tracking of a battery-powered fan. We spent most of our time trying to decide whether the room’s thermal energy increases, decreases, or stays the same. We touched upon lots of everyday experience–running the thermostat in your house switched to “A/C”, “Heat”, or just “Fan”; actual temperature vs. “feels” like due to wind chill, fanning to “cool yourself” off, you don’t seem to cool down the room; how the moment you stop fanning, the cool feel goes away; how ridiculous it seems that you could really cool off a room by having lots of people fanning, vents in your car, etc.
Eventually, people were convinced that fanning didn’t actually reduce the temperature, but we didn’t have an explanation for why you felt cooler. The idea that was eventually was proposed was, “Fanning helps the thermal energy you’ve produced around you go away, by blowing the warm air away from you.” Several said that there mind was blown at hearing that idea.
Eventually,everyone agreed a room should technically get hotter, but you wouldn’t be able to tell via “Amy’s pee theory.” The room is so big that the little bit of thermal energy put off by the motor wouldn’t make a big difference. This nicely motivated why we should try the experiment with a fan in a very small “room”. So we ran a fan inside a small cooler for 10 minutes while we went outside to make moon observations, and the temperature inside the cooler had risen by 12 degrees. Pretty cool. Upon opening the cooler, pretty soon the cooler was back to being normal temperature, because the “pee” that we had kept trapped in a toilet had now spread out into the pool. The room was not measurably hotter as a result.
After the experiment, someone blurted out remembering a long time when their house had been flooded. To dry out the house, they had to bring in dozens of industrial fans, and they recalled how freakin’ hot it made the house. Bringing in dozens of huge fans was like getting several bus full of kids to pee in the pool.
My inquiry class is going quite well this semester. The skills that this class has picked up quickly and use regularly include
– Re-voicing and paraphrasing what others are saying
- Asking questions about others’ ideas to get more information
- Asking questions to make sure we understand each others’ ideas
- Summarizing, comparing, contrasting different ideas that have been said
- Telling someone if/when their ideas make sense (even if one don’t necessarily agree), and why it makes sense.
- Talking to each other for extended periods of time (without looking at me).
- Using tone of voice / eye contact to indicate interest, care, and humility (rather than dismissal, indifference, and righteousness)
- Posing honest questions and making honest statements
- Using tone and body language that communicates that everyone is free to change their mind
Part of this reminds me that “being” a good listener and “being” engaged consist of things you actually do. But I’m also reminded of just how easy it is for everyone to do these things when everyone feels the right way–feeling safe and having a sense of belonging. Of course I know that there’s feedback between feelings and behavior: the students feel the way they do because of they way we are all behaving, but we are also behaving these ways because of the way we feel. It’s mutually reinforcing. And, of course, when these feedback loops are going the right way, it seems easy, like how could it be any other way. But I know that other times, when the feedback loops are going the wrong way, it can seem impossible. Cherish the good times.
One of the topics we teach in second semester physics is blackbody radiation. The typical kind of scenario students would be asked about is, given the temperature of a star and information about the size and orbit of a planet, determine how much energy arrives on the planet each second. One of the main difficulties students have is deciding how to use the relationship that intensity = power/ area. There are lots of different energies, areas, and intensities to consider, so students who are used to plug-n-chug can easily fall apart here. Since we introduced the topic two weeks ago, I’ve been starting each day with various discussion (clicker) questions asking student to think about intensity, energy, and power qualitatively. We’ve had lots of good days of discussion stemming from this and progress is certainly being made, but students’ handle on the ideas seem to be quite elusive and fleeting with lots of side-steps and backslides, even for the students who don’t usually struggle. On Thursday, I asked the following question to start our day, which pulled us into a really good discussion that lasted 15-20 minutes or so:
Assume you know how much energy is emitted from a star each second, Es. You want to find the intensity of the light arriving at a planet. Which calculation should you use? The question included a diagram that showed three distancse: Rs, the radius of the star, Rp, the radius o the planet, and Rsp, the distance between planet and the sun. The four options where.
A. Es/ 4πRp²
B. Es/ πRp²
C. Es/ 4πRsp²
D. Es/ 4πRs²
Students thought to themselves, voted, and then talk in groups. When students re-voted, we were split between B and C, with a few unsure whether it was A or B. We’ve been getting used to these kinds of discussions, so I asked a few students to explain why those chose B. The basic line of reasoning was that we were interested in the intensity at the planet, so the relevant area had to be the area of the planet, because the planet that was catching the energy with its cross-sectional area.
Instead of letting people voice an argument for C, I said that those who picked C had to explain what they was wrong with B without explaining why they thought C was correct. I motivated this by talking about why so many hot button issues arguments are unproductive, such as abortion rights, whereas everyone just keeps repeating their arguments without listening to the other side.
One really nice argument, which ended up being convincing to most in the class, was this:
- Es/ πRp² says in words that you are taking all the energy from the sun and spreading it over the area of the planet. This can’t be right because not all the energy from the sun gets to the planet. In fact, most of energy misses the planet because it goes off in other directions.
I made sure at least one other student could repeat the argument, and then another argument was made: This argument was about how we could actually “correct” the equation so it did give the intensity at the planet. The argument was that if the “area” you want to divide by is the area of the planet, than the numerator has to be energy arriving at the planet Ep, not Es. Intensity *is* an energy divided by an area, but to get the intensity of the planet using the area of the planet, you have consider the actual energy arriving at the planet, so it would be Ep/πRp².
By the time we got around to asking for arguments for C, most students were convinced it couldn’t be B, but formulating good arguments for C was hard, and it took a bunch of back and forth among the students before a really compelling argument to emerge. The discussion was really juicy and students were really listening, but I had a feeling that while the “class” a whole was getting it, many students still needed an opportunity to pull it together, consolidate. So I had students vote with thumbs up, thumbs side, and thumbs down, whether their understanding was , “I understand the reason why it must be C, and could explain it,” “I think I understand why it must be C, but I’m less confident I could explain it someone else,”, “I’m still not sure I understand why it must be C”. The room was split about half between thumbs up and thumbs to the side. I said if your thumb was to the side you had two options: you could look to a person with their thumbs up and tell them that you want to practice explaining it to them OR you could ask them to explain it to you one more time. I’ve never used that move before (giving the students who are unsure the option to either practice explaining or receive an explanation), but for whatever reason, it was the right move at the right time. The entire class in pairs and groups erupted into conversation and spent a long time explaining to each other–serious, passionate, intellectual talk with gesturing and smiles. I just stood at the front of the room and watched and waited for the talk to subside. It took a long time. I had a few more clicker questions, which we breezed through. Many groups told me that while they were discussing alone, they had actually spontaneously asked of themselves and discussed the questions I had posed.
I wanted to jot down this brain dump, because I thought the two counter-arguments were really fantastic, and I wanted to think about why this particular talk move worked so well. Part of it is that they were just primed and ready to talk about it more, but I think there was something about putting the power in the hands of the person who doesn’t understand. They were in control-they could demand to hear an explanation or demand that someone listen to them.
Monthly physics teacher meetings:
Since September, our Department has been hosting a monthly event for local-area physics teachers. We usually have some time at the beginning for demo-sharing on a specific topic area, then we provide dinner and some time to chat, and we usually end the evening by engaging the teachers in some sort of physics/physics teaching activity. So far we’ve had 5 meetings, and we’ve had lots of good feedback from teachers. About 6-20 teachers have been attending. Hoping to continue to nurture this and thread this into some grant proposals.
Learning Assistant Program Pilot:
Last semester, two faculty in our department attended the LA workshop at UC Boulder. This semester we are piloting some curriculum changes and use of learning assistants. Right now, we are only implementing in two section of our intro physics course and most of our LAs are already physics majors in our physics teaching concentration; but the plan is to implement more widely and to recruit students to be LAs for next academic year We’ve applied for some money that will hopefully help out with that. I’m not teaching in these section, but I have responsibilities for running the prep session with the instructor and the LAs for instruction each week. I have a undergraduate student who is also helping to collect data regarding this pilot implementation.
Two New Preps:
This semester, I’m teaching three courses, but two of those courses are ones I hadn’t taught before at MTSU. The first one is the second semester of the algebra-based physics course, which covers optics, modern physics, and electricity and magnetism. It’s been nice to have a different course to teach, but it’s meant more prep than usual.
I’m also teaching a new course for the first time. We had previously had a one semester seminar course called “Physics Licensure”, which was intended originally to be a self-study-kind of course for future physics teachers to make sure they were prepared for the Physics Praxis. We’ve made that a year long seminar now, in which we focus more on developing conceptual understanding / qualitative reasoning with 1st-year physics topics (and less on praxis prep per se). Students also have responsibilities for working on AP physics problems. This semester is the first time the second-semester of Physics Licensure is being offered. Right now the two courses are still kind of playing the role of “band-aid”, making up for deficiencies in our first-year courses. We are working to improve our intro courses (see above), so the nature of these courses may shift.
On top of this, I’m working on a grant that doesn’t overlap with any of the efforts described above and trying to finish a paper that’s been in the works for years that also doesn’t concern these efforts. The next time I write a grant, It’ll need to be more synergistic with my service and teaching efforts.
One thing that’s been on my mind is the extent to which our physics teaching majors are or are not developing identities as physicists/physics majors. Coupled with this issue of identity development is the concern that our physics teaching majors are not strongly integrated socially and academically with the rest of the physics majors.
There are a couple of factors driving this:
Physics teaching majors are not merely physics majors. They are also MTeach students. MTeach has a strong presence in their undergraduate trajectory. More specifically, students in a particular cohort are likely to take eight courses together to fulfill their minor in secondary education. MTeach has a very nice informal gathering space, where MTeach students hang out, get work done, etc. It’s a place where students are forging their sense of belonging in a community and developing identities as math and science teachers.
Most, but certainly not all of other physics majors, go through the calculus-based introductory physics sequence. In their sophomore year, most physics majors take a year of modern physics and a year of theoretical physics (i.e., math methods). So in the first two years of the program, a cohort of physics majors will have taken 6 physics courses together. Being in those courses and hanging out /working in the physics majors lounge working is partly where physics majors forge their sense of belonging to the community and develop identifies as physics majors / physicists.
Most of our physics teaching majors, however, are going through the algebra-based physics course, not the calculus-based course with the physics major cohort. For some, this is because they decide they want to pursue physics teaching only after taking our algebra-based physics course. For those who know early on they want to pursue physics teaching, it’s likely they don’t take the calculus-based course because they haven’t taken calculus yet, and are advised to take the algebra-based course. And while the graduate school track physics major concentrations require that students take the sophomore year theoretical physics course, physics teaching majors don’t have to take theoretical physics if they take both linear algebra and differential equations from the math department. So far, very few physics teaching majors take theoretical physics.
What does this mean for our physics teaching majors? In the first two years that our physics teaching majors are in the program, they take only two physics courses with other physics majors–the year of modern physics in their sophomore year. They don’t become integrated deeply at all into the a cohort of physics majors, because they weren’t in the same courses freshman year and then they don’t struggle through the very challenging calculus-based physics and theoretical physics course with the rest of the physics majors. Most of the physics majors go onto take a demanding course load in their junior and senior years, including a mix of required and elective courses, including some courses that verge on graduate level work like courses in quantum field theory, general relativity, etc. Physics teaching students take a few more required physics courses at the upper-level (e.g., thermodynamics), but they have less required physics content courses (in part) because they are required to take a sequence of physics teaching courses offered in the department. This is just to say that, even in their junior and senior years, physics teaching majors are unlikely to have social or academic interactions with the rest of the physics majors. And while they could elect to take more upper-level physics electives, they are not likely to, in part due to peer groups but also because many physics teaching majors are dual certifying in mathematics, so they are busy taking other content course in the math department and their education courses which required a lot of field experience time.
I’ve been thinking about this a lot recently, and then it really hit me hard last night when only one physics teaching major came to the annual physics department pot-luck / party / gathering. Not surprisingly, the one physics teaching major that came is quite socially integrated into the physics major cohort, chose to do research in physics not physics education, and elected to take theoretical physics even though it’s not required.
I’m not quite sure what this all means yet, and there’s other issues at play that I haven’t described, but I’m thinking hard about this. The issue of navigating multiple communities is complex, and I’m hoping by choosing to write about some of this that I will develop some insight into what this all means.
One interesting physics conversation this semester has been about how we categorize forces. One future physics teacher in particular kept being concerned about whether to call something a tension force or a normal force. For example, consider the following situations:
- A chain, consisting of many links, hangs vertically. The very top link has a rope wrapped around it, which keeps the whole chain fixed to the ceiling.
- A rope is wrapped around a box and pulled by a person.
What kind of contact forces act on the top link? What kind of contact forces act on the box?
I think many students learn to associate types of forces with kinds of objects. For example, objects like ropes and strings exert tension forces. Objects like walls, ramps, and tables exert Normal forces. Springs, of course, exert spring forces. This kind of object-focused categorization means having to have a category for forces from a hand, like “Applied Force”
If this is how you think about forces (in terms of object categories), both the link and the box have tension forces exerted on them by the ropes, because ropes exert tension forces.
Another way to talk about forces, however, is to focus on mechanism. This is how I, and many other physics teacher I know, talk about force. Normal forces are contact forces arising from surfaces or points of contact that press into each other. In other words, Normal forces are compression forces. Tension forces are contact forces that result in points of contact that involve stretching. Friction forces involve sheer. Compression, tension, and sheer are about what’s happening at a point of contact not about what kind of object is exerting the force. A hand that pushes, of course, is just a normal force, because your skin cells are being squished not stretched.
It took me a while to really get insight into the students’ concern, but as we talked more and more I realized his concern resulted from the juxtaposition of these two ways of categorizing force. In the two scenarios above, the part of the rope that is contact with the object is being compressed. If one is attending to the mechanism, then you’ll conclude that it’s a Normal force. If you are focusing on the kind of object it is, you’ll conclude it’s a tension force. This contradiction troubled the student.
The question remained, however, how should we resolve the conflict? At first, I was being a very bad debater. I just kept repeating my own arguments about normal forces being compression, dismissing altogether the issue of what kind of object it was. Now, I do think that categorizing based on mechanism is more useful than categorizing based on objects, but merely repeating my view was not going to help us understand the real issue. It wasn’t helping either me or the students get a deeper understanding. The real issue came about by thinking about grabbing someone by their shirt and pulling them toward you. In this case, if we choose the person’s naked body as the object of analysis, then the shirt is compressing against the person’s back pushing them forward, meaning there is a normal force. However, if we choose the object of analysis to include their shirt, then we could conclude that the shirt/person system was experiencing a tension force. If you get really picky about the exact boundaries and how the hand grabs the shirt, you might even conclude that the force exerted by hand on the shirt/person are some combination of normal forces and friction forces. The key point is that we could certainly draw the boundary somewhere around the person (e.g., including most of but not all of the shirt) where the force at the boundary is a tension force.
The thing we realized is this: The ambiguity about whether something is compression or tension goes away when you attend to both mechanism carefully and attend to system boundary carefully. Small changes in the exact location of the system boundary (naked body or naked body + clothes) matter for whether the points of contact at the boundary are in tension or compression. That’s because even a single object can have places that are in tension and that are in compression. If you slice the boundary over a region that is compressed, your going to have normal forces. If you slice the boundary over a region that is being stretched, your going to have tension forces. The shirt example helps, I think, because of it’s a subtle shift in boundary.
With the rope around the box, if you are serious about only including the box in your system, then there is no tension force. However, if you drew the boundary around the box a bit farther out, such that the rope around the box was in the system, then the force acting on the system is a tension force. The truth is, as an object, a lot of the rope is in tension. One thing you realize in thinking about this is that tension forces can’t arise with out adhesion or bonding. If you haven’t adhered a rope to an object, it can’t exert a tension force.
What’s interesting is that this is the complete opposite of what I’ve often heard said to students. Students are often told that ropes can only pull, not push.
This year in inquiry, we started with light as usual, but now we are moving on to energy. We’ll be conducting our own energy inquiries as we also analyze and discuss Sharon’s 3rd-grader’s inquiry into energy at the Responsive Teaching in Science Website, reading the book she co-authored called, “Becoming Scientists“, and talking over skype with Sharon about teaching science.
Below are excerpts from students’ first assignment that are still coming in. We have actually not discussed energy at all in class. Students were asked to write about an object or activity in their house that they think involves energy. Here is just a peek into what students are writing:
I think that fans are powered by electricity/energy and this allows them to move in a circular motion to create air flow. This makes sense because in order for something to move it would need energy. To me, it has always made sense that anything moving has some sort of energy asserted on it. Usually when things move other objects, then the object gives energy and the object receiving the energy is using it. I think that energy is needed in order to make fans work because without energy it just wouldn’t move at all. The fan wouldn’t have anything to power the engine.
I know that light uses electricity which I think is powered by energy. I know the term “electrical energy”, so this leads me to believe that electricity is either a type of energy itself, or is powered by energy. Energy has to be present for the light to turn on. I believe that energy sends electrons to the light and the electrons make electric energy which causes the light to turn on.
I do know that there are different types and different ways energy is transferred and/or released. I know that the energy starts somewhere and is transferred through wires through an outlet in my home. Then, the energy is transferred again through a lamp, air freshener, or TV. My question now is where does energy begin during this process? I understand that energy can move from source to source but where does it begin in this scenario? For example, a child pushes a ball. When the child pushed the ball, energy was given off and transferred onto the ball. What is the “child” if you will through using an electric outlet?
Energy results in an action. A lamp being turned on is evidence of a change or an action. Energy had to be used to create that change. Energy was transferred from the outlet to the source in this case, a lamp. Energy is needed to make this action happen because a lamp is not going to turn on itself. A TV needs another source to “wake up.” The way I look at it is this way: everything is at rest, there must be an action that “wakes up” an object to get reaction desired. In this example, energy is being used through electrical outlets. Energy transferred through wires to the electrical outlets, this process causes many different objects to “wake up.”
When I think of energy, I think of any type of movement: Even if an object only moves or works because of another source of energy—the stationary object is still using energy.
In the case of playing the piano, I am using energy in all sorts of different ways. In a sense, I am “giving” or “transferring” my energy to the piano to make sound. I think of energy almost like a chain reaction or domino effect—the energy used or transferred happens so quickly that it’s almost unbelievable!