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All material is my personal opinion, and not that of any other organization. Copyright 2001. Permission is granted for individual teacher use. All rights reserved. |
Sep. 11, 1997 Anthony! First of all, the year's going great! I'm finding myself in the middle of quite a successful inquiry-type experience... These last two days, my classes have observed what happens when you add a drop of food coloring to the top of a glass of hot water vs. what happens when you add it to the top of a glass of cold water. This is a GREAT activity! We've hypothesized reasons for some of the observations we made (in particular, the one which was uncontested was: the dye "spreads out" faster in the warmer water). A few students in each class came up with VERY imaginative hypotheses, after I urged them to be creative, saying that's what scientists do when they try to figure out how the HIV virus gets into white blood cells, for example. (Does it use molecular pliers? Does it burn its way through chemically? Does it trick the blood cell?) One student shared that the hot water was heated, sterilizing the water, killing the bacteria in it. With less bacteria, there will be fewer obstacles for the dye and so it will be able to spread out better. And there were others - some said the spreading out was caused by the DIFFERENCE in temperature between the dye and the hot water. Now here are my questions for you: I'm planning on having students test some of these hypotheses. Any suggestions for how to maintain student interest on a question which originally hadn't interested them THAT much? They did all become very attentive when people were explaining their ideas, so I think there probably is potential for continuing with this. How will I ultimately make a case for the molecular explanation (ie the water molecules that are bumping against the dye are moving faster in the warmer water)? How do we know that another student of mine wasn't correct when he suggested that the hot water is actually DISSOLVING the dye - ie (as he said), breaking the bonds between the dye molecules. How do we know there aren't bonds between dye molecules? Is the best procedure simply to see which hypotheses can be eliminated? How could the class be arranged to consider these hypotheses when there are only about 4 or so that I can imagine testing? What do I do with hypotheses that are untestable? How far do I take this (we could always come up with improved hypotheses)? Another hypothesis: chlorine in the water is trying to clean it up; chlorine therefore tries pulling the dye apart. Chlorine works better in warmer water. How do I deal with unhelpful hypotheses (eg, "it spreads out more quickly in the warm water because of the higher temperature")? I'm looking forward to your ideas. I'm excited about how things are going; I'm also curious about how your kits are working. - Marc Marc,Your inquiry sounds great. The only trouble I see is that you are working with something that is occurriing on a molecular level, and therefore is impossible to observe directly. I assume you want students to arrive at some sort of kinetic model. The first issue the students must confront is how to actually test their idea. If an idea can be investigated, then it is a good one to work on. The suggestion that it is because the water is warm is really observational, not explanatory. We still need to ask what it is that is different about warm and cold water. The two hypotheses you mentioned, related to bacteria and temperature difference, can both be tested directly. I would go through all the hypotheses with the class and discuss which are investigable and which are not. Then, I would challenge the students to come up with experiments to test those that are investigable. For example, you could buy distilled water to ensure a lack of bacteria. You could heat the dye to avoid a temperature difference. But the students should be able to think of these experiments. I would get the whole class interested in testing these hypotheses, and do them as a class. Unfortunately, these hypotheses are likely to be disproven. Has anyone suggested a correct hypothesis? Have you any idea how you would demonstrate diffusion on a larger scale? One idea I saw in a book call "Teaching Physics With Toys," involves using an electric game called "Bedbugs." The game features a board, with a host of plastic bugs sitting on a platform. The platform is vibrated by an electric motor (to which you are supposed to add a rheostat to simulate temperature differences). As the platform buzzes, the bugs diffuse. The kids can see the kinetic motion of the bugs, and perhaps will visualize what is occurring at a molecular level. It would be best if the kids could come up with their own accurate hypothesis, and a way to prove it. But I think you need to be prepared to help them out. Unfortunately, I cannot think of a way of directly demonstrating the kinetic theory. I agree that you could have a category for "unproved hypotheses," but you should point out that to be workable, a hypothesis must be testable. I don't think there is anything wrog with wrapping up with a reading on the theory accepted by scientists, and perhaps even a historical review of how it was originally discovered. Students could then compare their hypotheses and investigations to those of scientists a few centuries ago, and see the parallels. I am thrilled that your kids are engaging in this process with you. If you keep things moving along quickly, and provide the means by which they can test their ideas, I think their interest will remain high, even if they are investigating someone else's hypothesis. As far as my kits go, I haven't used them yet. As you know, I am part of a development team, and we are doing some preliminary work to establish classroom management first. I hope to begin using them soon. Keep up the good work! Anthony |
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