What is a "Mystery Tube?"
Simply, a "mystery tube" is a closed pipe with four ropes emerging near the ends, on opposite sides.* Pull a rope, and any other rope(s) that are out will get pulled back in. It doesn't matter which rope you pull; any and all ropes already out will mysteriously slither inside. It can be inferred that the ropes are connected inside, but you can't see how. See my Youtube video for a visualization and explanation.
Students watch this strange phenomenon and are immediately fascinated, because the strings seem to behave in contradictory fashion. Sometimes students are tempted to say, "I know what's going on inside," even before they have been able to make any careful, systematic observations. "They are tied in a knot on the inside." They are always wrong when they say this, because what is "obvious" in this case is incorrect.
The Mystery Tube
How I Use this in the Science Classroom
I am thoroughly convinced of the importance of "inquiry" in science education. "Inquiry" simply refers to allowing a student to make her own observations, pose her own questions, launch her own investigations, and come to her own conclusions. Inquiry is opposed to "Didactic," which is when an educator is merely a transmitter of information. This is not to say anything against didactic lessons, only that students are forced to passively experience them rather than be actively engaged. I use some elements of each in every lesson I teach, but I try to lean toward inquiry. Students have more control and choice in these lessons, which is positively correlated with both salience (perceived importance) and motivation. Inquiry can be applied in any subject, but science by its nature is especially well-suited to inquiry.
This lesson is an excellent introduction to the nature of science and scientific methods. The tube is mysterious enough that it engages students for two whole class periods, and with proper guidance, students can see for themselves how they should conduct an investigation to understand the workings of the tube.
The Lesson in a Nutshell
Day1:
I begin by pointing out that all scientists have common habits of mind, ways of observing, and ways of answering questions about the world. These habits are collectively referred to as "scientific methods." Now most students are familiar with "the scientific method," (observe, question/hypothesis, experiment, analysis, conclusion) but I make sure that they recognize that there are other ways to do science that don't fall strictly in line with "the scientific method." For instance, sometimes scientists will hopscotch from one step to another, or not conduct what is considered an "experiment."
I have a volunteer play with a tube in front of the classroom, to immediately hook students. I give each group of two partners one mystery tube to observe for themselves. Then I give each student a data sheet that includes spaces for a single question about the tube, how they will make observations, the observations themselves, a space for a drawing of the inside (their hypothesis), and how they could test their hypothesis.
This is a good opportunity to point out that a hypothesis is not simply an "educated guess," which is the stock definition provided by unimaginative grade-school teachers. How is a fifth-grader supposed to make sense of what an "educated guess" is? Their drawing is a proposed explanation for how this system works, and the explanation can be tested. This is what a hypothesis is. Some of their hypotheses are shown below.
A B C
D E
Some students suggest that there is a "device" holding the strings together inside, as is seen in hypotheses B and D. In B the device is fixed while in D it lets the strings slide freely. B and C both involve knots.
After they have drawn their hypothesis, I guide them toward how they may choose to test it. This test serves as their "experiment." I don't discuss variables or the proper definition of an experiment here, only that an experiment is how scientists test their proposed explanation. Most students suggest that they could cut the tube open, but this would really just be making more in-depth observations, so it is not an experiment. It is also not allowed. Eventually some students suggest that they could build a small model with common materials, such as toilet-paper tubes.
It is at this point that I collect the tubes and explain to students how they will test their hypotheses, by building small models using string, tubes, and any other materials they think they need.
Day 2:
Students come in on day 2 excited and ready to test their hypotheses. Some even build models at home on their own initiative, so they were already able to test their hypothesis (they like to brag about this).
I let each group take a toilet-paper tube and two or three strings of yarn already cut to a length of about 8 inches. I also provide paper clips for the "device" some of them proposed in hypotheses B and D, scissors, compasses, and wooden skewers to help them punch holes. I give them the tubes again so they can compare their model's behavior with that of the tube.
Students have 35-45 minutes to test their hypotheses, and I leave all the specifics of their models to them. Some students stop after their first test and realize that their hypothesis is completely bad, such as A shown above. Some are at first convinced that their hypothesis is good based on their model, but they just need to make a few minor improvements (such as where the knots are located), as in hypotheses B and C. Others are able to design a model that behaves 100% like the Mystery Tube, which indicates that their hypotheses are "good." D and E were good hypotheses.
Discussing the Nature of Hypothesis and Certainty
I discourage students from considering their hypotheses "right" or "wrong," but rather "good" or "bad." Their hypothesis either explains the observations (it's good), or it does not (it's bad). I point out why this distinction is important: I (sarcastically) hypothesize that there is a tiny man inside the tube, who pulls the strings in a certain way when I tug on the others. This hypothesis cannot really be proven to be "wrong," however it can be shown to be "bad" based on what we know about humans (they can't fit in a 1.75 inch PVC pipe). Conversely, a hypothesis that works- as illustrated by experiment- can be "wrong" even though it is "good" in that it is consistent with observations. D and E shown above both work perfectly, even though the "right" one is D. We could talk all day about these distinctions, but after some discussion, students understand what is meant by a good or bad hypothesis and that a good hypothesis is "possibly right," while a very bad hypothesis is "not possibly right."
I grade students on participation, because some of them work very hard to improve the model for a hypothesis that is pretty bad. This shows persistence to understand the tubes. I want them to know that I value their investigation, even if they never developed a "good" hypothesis (almost all of them did).
The photographs below show the actual arrangement inside the Mystery Tubes, as correctly hypothesized by some of the students.
Should I Tell Them?...
By the way, I never reveal to students exactly how the tubes work. A practical reason is that I don't want their younger siblings or friends to come in next year already knowing how it works. The educational reason is that I want them to understand that "the best explanation" is sometimes as far as you can get in science, and very often a hypothesis can in no way be "proven," that is, known with absolute certainty. An epistemic philosopher would have a lot to add here, but an epistemic philosopher I am not. Enjoy!
*Credit for the idea for the lesson plan and Mystery Tube design go to Dr. Pablo Llerandi-Román, of the Grand Valley State University geology department and instructor of the course Earth Science in Education.
No comments:
Post a Comment