[music] Kristin Mayer [voiceover]: Early in this unit, students made observations of several phenomenon involving Van de Graaff machine. One of those phenomena was observing what happens when pie pans are stacked on top of the Van de Graaff machine and machine is then turned on. Students observed that the pie pans then flew off the Van de Graaff machine. In this video clip students are making revised models of that phenomenon, using evidence they’ve been, collecting throughout the entire unit. You’ll see the students are initially working on their model while the teachers are circulating. As I circulated I worked hard to point students to evidence as opposed to answering their questions directly. After students have worked on their models, we then have a whole class discussion of their revised models. Ms Mayer: So, do you think in the beginning, before it was turned on, was it charged? Student 1: Hhhhm, no. Ms. Mayer: Why, so why did the pie pans fly off? Student 1: Because of the charge Ms. Mayer: okay, so what additional components could you add? Student 1: Positives and negatives Ms Mayer: So, if the pie pans are negative, and the Van de Graaff is positive, what happens if we have negative and positives opposite? Student 2: change the charges, Student 3: Woah, woops,, Ms. Mayer: Okay, so you’re saying that the Van de Graaff is positive and that made the pie pans and positive? Student 3: Mm-hm Student 2: sure Ms Mayer: So you have the pos- the Van de Graaff is positive and the pie pans are negative and the Van de Graaffs are positive and the pie pans are negative, so what’s different between when we from when it was off to when we turned it on? what did turning it on do? Student 4: Oh, make this negative? Oh, what, what’s it Ms. Mayer: So, were do you think the charges come from? Student 4: The, Van de Graaff? Ms. Mayer: Okay, so before we turn the Van de Graaff on do you think it’s charged? Student 4: Oh, no. Ms. Mayer: So when it’s off, what would we have Student 4: No charges. Ms. Mayer: okay Student 4: Right? Cause it’s not on yet? Ms. Mayer: Okay, well, what do you think Matt? Before, when it’s off would there be no charges, because it’s not on yet, or do you think, Student 5: No charges. Ms. Mayer: No charge, so you agree? Okay so then, and then if we have negative and positive what happens when we have opposite charges? Student 4: They attract, so then these would be repelling if their fly off, so, Ms. Mayer: So what charge you think those are? Student 4: positive. Ms. Mayer: Okay. Ms. Mayer: There are a few things I want to point out about the interactions as I walked around helping students with their models. One is whenever I’m working with students, I try really hard to respond neutrally to all of their ideas. I do this because I want students to gain competence based on the evidence they’ve gathered as opposed to my reaction to their ideas. This means students don’t always have correct responses. For example, one other group had an inaccuracy in our model. They said that the Van de Graaff machine was positively charged before it was plugged in. When I walked away, the students still had that inaccurate idea. I made the choice to leave that inaccurate idea in the students’ models because I wanted students to have the opportunity to correct their own ideas rather than the teacher always been the evaluator of their work. So, by leaving that inaccuracy on the model later during the whole class discussion, you’ll notice that provided the opportunity for a question to be raised about whether the Van de Graaff machine should be neutral to start or positive to start. I don’t like to have the group present their models. Instead I found that students have better discussions when the models are anonymous. Having the work presented anonymously is part of building a safe environment for making mistakes and changing ideas. Also I found that students often give more constructive, critical feedback when they do not know who drew the models. I have students set up their model, so we can compare across them I always start by asking students for similarities and differences the students notice when comparing models. Then I ask the students to evaluate their models by asking how well the models explains our observations. Ms. Mayer: Alright, so if we turn around and look at our uh, models that we’ve created this time. So again when we’re looking at our models, we wanna think I of the components that you guys included, the relationships that are shown between those components, and then how well that explains what we observe. Alright, so, models always have to connect to the phenomenon. So let’s go back what did we observe? But wha- so with the Van de Graaff machine like second week of school what was the observations with the Van de Graaff, what were the observations with the Van de Graaff machine, specifically? So, I piled up the pie plate pans on top the Van de Graaff and what happened? Kenzie, what’d we see? Student 6: On the Van de Graaff? Ms. Mayer: yeah Student 6: They fell off Ms. Mayer: They just like slid off the sides? Student 6: They pushed off Ms. Mayer: They flew off? Student: Yeah Ms. Mayer: Okay Anyone want to add anything to that Yeah, Jake? Student 7: I think that the shape of the pie pans could’ve had an affect on their path they traveled, because if they were just, just like flat, sitting on top I think they would’ve kind of went like this and slid off, but because they were Ms. Mayer: Curved? Student 7: curved they went more up. Ms. Mayer: Up? Okay, all right so, at first they were like sitting on top in balancing their because
of the shape of them and then when we turned it on they flew up and then fell as opposed to just sliding off. Is that what you were saying? Okay. Alright, so if we look across our models, and don’t miss these two over here, any common components, anything you guys notice? Student 8: I see a lot of Van de Graaffs Ms. Mayer: All right, a lot of Van de Graaffs,, and pie pans. Any other components in common? Multiple comments: positive. A lot have cords. Positive Ms. Mayer: Alright, positive charges Student: Arrows. Ms. Mayer: Arrows, to show the relationship Student: Words. Ms. Mayer: Words. Do we know that the Van de Graaff is positive? Alright so, Blake, what evidence do we have that the Van de Graaff was positive? Student 8: Cause you said it was Ms. Mayer: Yeah, Ryan? Student 9: Uh, I , believe it was the same reason but also the same reason since the pie pans flew off that they, um, would repel so that um,
the opposite charges push each other away and different, um, charges would’ve been repelled
away. Ms. Mayer: so the, the pie pan are the same charge as the Van de Graaff or opposite charge? Student 8: Opposite Ms. Mayer: So, opposite charges do what? Multiple responses: They re-. They attract. Ms. Mayer: Opposite charges attract? Student 9: Oh, sorry, I meant the other way, the other way around. Ms. Mayer: Other way? I do that a lot too Ms. Mayer: So pie pans are the same charge, or opposite charge as the Van de Graaff? Student 9: Same charge Ms. Mayer: Same charge? Okay. Something to add to that? Student 3: I thought we proved it because the negative balloon was attracted to it. Ms. Mayer: Yeah, so I actually, cause you said I told you, I actually didn’t know that the Van de Graaff was positive but we tested it with the negative balloon right and we stuck the balloon on top and then turned it on and we saw the balloon like stuck to the Van de Graaff when we turned it on, and we know the balloon was negative So there’s some evidence that we use to inform these models. And then we turned it on we know that the Van de Graaff is positive, how about the pie pans? Student: Positive Ms. Mayer: Positive? Why? Student 8: Because the Van de Graaff was positive. Ms. Mayer: Okay. Student: And we saw them repel. Ms. Mayer: Alright so we know that the Van de Graaff is positive and we saw they repelled. Jayla, did you have something to add to that?
Student 10: Oh, I, was gonna say, cause like charges repel from each other. Ms. Mayer: Okay, and so, from our, our evidence we’ve gathered we know that like charges repel. Um, where do you think the pie pans are getting their charge then? Multiple responses: The Van de Graaff. Air? Ms. Mayer: From the Van de Graaff? Multiple responses: Yeah, yeah. Ms. Mayer: Okay Ms. Mayer: So the, the pipe and before we have neutral then we plug it in and the Van de Graaff becomes positive and that makes the pie pans positive? Multiple responses: Maybe. Yeah. Ms. Mayer: Maybe? Okay and then we see them repel so we have some arrows showing them repelling. So what do you guys think do these model do a good job of explaining our observations? Multiple responses: Yeah. Some of them don’t Ms. Mayer: Some of them don’t? Student 8: Because some of them say it was positive before it was plugged in. Ms. Mayer: Okay. So we had, if it was before would plugin that doesn’t explain our observation that in the beginning nothing was happening, okay. So we could maybe edit some of the before to make it more clear why we didn’t see anything. Student 1: That one makes the pie pans negative and the Van de Graaff is positive Ms. Mayer: Okay. So if we had negative pie pans and positive Van de Graaff what would we see? Multiple responses: Attract. They would attract. Attracting. Ms. Mayer: They would be attracting not repealing So some of these do a good job of explaining observations but someone we could maybe make some edits in line with our, the evidence we’ve collected? Yeah? Okay. Kristin Mayer: This is a discussion about a topic this class has been studying for a while the goal of this discussion was to develop a consensus about what was happening in the phenomenon. However I still want students to be basing their answers on the evidence they have collected not my reactions. So I still try to respond neutrally and ask for additional input or alternative ideas from students. Since we were building a consensus when a student made in inaccurate statement I asked some follow-up questions to see if he misspoke for was confused. When he realized his mistake I pushed him to restate his answer to make sure we’re on the same page. If it had been a discussion at the initial ideas, I would not have pushed him to correct his answer but instead pointed out the different thoughts students have about the interaction. In this discussion I did ask quite a few questions that had straightforward and simple answers. Normally I would try to ask more how and why level questions but the students were being unusually quiet so I made the decision to switch over to simpler questions that had more straight forward answers as a way to get the discussion started then once teams were talking we coul transition into deeper level questions. In the next clip you’ll see how the questions that were left unanswered after the students concluded their final models were used as a transition into our next topic, which was beginning to look at atomic structure [music]