Last year I supervised Erin Kennedy’s honors thesis research. Erin plans to be a teacher, so she was interested in doing a thesis on physics education. Her project involved studying how well students understood some basic ideas about mechanical waves. Her guinea pigs were last year’s Physics 2110 and Physics 1502 classes, which I taught. She gave the second years a diagnostic test (developed by Wittmann as part of his 1998 PhD thesis at the University of Maryland) early in the course, and again at the end. She analyzed the results of the pre-test to see where students held misconceptions about wave physics, then designed and delivered lessons intended to help correct these misconceptions. The post-test was intended to show how well the students’ understanding improved as a result of the inspired teaching they received.
Wittmann had earlier used his diagnostic test on first-year students in the U.S. He (and earlier researchers) found that the students held a number of interesting misconceptions. For example, many students thought that if you flicked an stretched string harder, then the wave you produced would travel faster. (It won’t, by the way. The speed of the wave is a property of the string – it depends only on the mass density of the string and the tension, and doesn’t depend on the way the wave is produced. But you knew that.) Wittmann figured out that many students were taking ideas from their understanding of the motion of objects and incorrectly applying them to wave motion. In other words, students were trying to treat waves the same way they would treat a baseball: If you throw a ball harder, it moves faster. Therefore, if you hit the string harder, the wave will move faster. When I read Wittmann’s work, I was astounded by this. I had taught first-year physics, and waves in particular, many times, and I had never knowingly run across this way of thinking. Clearly students in the US must be a lot dumber than students in Canada!
Well, guess what Erin found? Our students are just as dumb as the US students. To be a bit more polite, our students held exactly the same misconceptions as those found in the previous studies. She did find that student understanding improved from first year to the end of the second year course, which is reassuring. In many cases, however, these misconceptions persisted even after the students had studied waves in first year, and then had a full course on oscillations and waves in second year! I confess I was surprised by this.
What I find really interesting, however, is that the same common misconceptions have been found in studies on students from the US, Canada, France, Australia, and Thailand. It seems that the misconceptions cannot be blamed on cultural factors or on a particular educational system. They are universal. I suspect the same is true of the common misconceptions that have been identified in other areas of mechanics. Why? Why would a kid from Thailand independently come up with the same wrong ideas about wave propagation as a kid from France? It must have something to do with the way our brains work, the way our minds try to make sense out of the world. It’s too bad that our brains evidently come up with something that’s not physics, but, to be fair, it took people as smart as Galileo and Newton to figure this stuff out in the first place!
