From Paul Camp: I like your text a lot, and it is one of the options I am trying to promote with my colleagues here. I think the problem book is a brilliant use of a Vygotskyian perspective.
But having spent some time with it, there are a couple of things that, while not exactly wrong, I think there are potential issues with. In one case, it is a potential bad interaction with known phenomenological reasoning patterns, and in the other it is a bad interaction with faculty of a certain background.
One is the argument used for acceleration on an incline. I see this in Knight too and it bugs me there as well (though your version is quite a bit better than his). I think you will agree that the argument is not physically correct, but is essentially a plausibility argument. To do it right, you need to sum the forces.
It is the sort of thing that appeals to a physicist as an elegant argument. But the reason it appeals to us is because we bring with us prior knowledge that makes sense of the argument. What we see in it, in the background, is forces.
It is, then, worth taking a moment to ask what prior knowledge students bring with them to make sense of that argument. What they bring is phenomenological reasoning (diSessa's p-prims, specifically the blocking and guiding p-prims). What they see is "the real acceleration is g, but the track is blocking." That is decidedly non-Newtonian reasoning and something I have seen in my students, using Knight's version of this argument, in the past year.
You appeal to experimental data rather than directly to a notion of blocking, as Knight does, but still that p-prim based reasoning has such a high activation priority that it is bound to be triggered.
There is data (I have some but others have more robust data) suggesting that the developmental processes leading to understanding of acceleration and of force are not independent, that they are in fact intertwined, bootstrapping off each other.
For that reason, my preference would be for introducing force and acceleration simultaneously, to build from the center out. In other words, organize the content developmentally rather than according to the organization that an expert sees. Make multiple passes. Then you don't have this specific problem because you will always be talking about net force. This is what Eugenia and Alan did in their algebra-based book, and what Ruth and Bruce did in Matter and Interactions. It strikes me as a right approach.
From Paul Camp: I like your text a lot, and it is one of the options I am trying to promote with my colleagues here. I think the problem book is a brilliant use of a Vygotskyian perspective.
But having spent some time with it, there are a couple of things that, while not exactly wrong, I think there are potential issues with. In one case, it is a potential bad interaction with known phenomenological reasoning patterns, and in the other it is a bad interaction with faculty of a certain background.
One is the argument used for acceleration on an incline. I see this in Knight too and it bugs me there as well (though your version is quite a bit better than his). I think you will agree that the argument is not physically correct, but is essentially a plausibility argument. To do it right, you need to sum the forces.
It is the sort of thing that appeals to a physicist as an elegant argument. But the reason it appeals to us is because we bring with us prior knowledge that makes sense of the argument. What we see in it, in the background, is forces.
It is, then, worth taking a moment to ask what prior knowledge students bring with them to make sense of that argument. What they bring is phenomenological reasoning (diSessa's p-prims, specifically the blocking and guiding p-prims). What they see is "the real acceleration is g, but the track is blocking." That is decidedly non-Newtonian reasoning and something I have seen in my students, using Knight's version of this argument, in the past year.
You appeal to experimental data rather than directly to a notion of blocking, as Knight does, but still that p-prim based reasoning has such a high activation priority that it is bound to be triggered.
There is data (I have some but others have more robust data) suggesting that the developmental processes leading to understanding of acceleration and of force are not independent, that they are in fact intertwined, bootstrapping off each other.
For that reason, my preference would be for introducing force and acceleration simultaneously, to build from the center out. In other words, organize the content developmentally rather than according to the organization that an expert sees. Make multiple passes. Then you don't have this specific problem because you will always be talking about net force. This is what Eugenia and Alan did in their algebra-based book, and what Ruth and Bruce did in Matter and Interactions. It strikes me as a right approach.