When Science Experiments Fail
I’ve mentioned before that I find it incredibly important for students to learn how to fail. Mistakes, errors, accidents, failures, mishaps, and so on are simply a part of life. It isn’t the falling down that is problematic; it is not getting up again afterwards. I believe strongly in teaching my students how to get up again, dust themselves off, and carry on, learning from the mistakes. This has application in social development, but it also has very real application in the academic realms of mathematics, literacy, history, and, of course, science.
Each year my students set up a science experiment in the classroom to go along with our unit on weather and the water cycle. We take a plastic Zip-Loc bag and place a small cup with some water inside it and hang them from the window. As the sun shines on the glass it heats the water, causing it to evaporate. The vapor then condenses on the side of the bag and precipitates down to the bottom where it pools outside the cup. Some years I have used food colouring in this process so that students can see that the dye is not actually water and therefore doesn’t travel with the water molecules.
I didn’t do that this year. I also decided to use test tubes instead of cups. They had been hanging on the windows for over a week when I noticed something: nothing seemed to be happening.
Each day I would come in and examine the 25 experiments set up on our windows. And each day I would notice that the water was still in the test tubes and that nothing seemed to be occurring. This was, of course, quite problematic, as it seemed as if my entire experiment had failed, despite having been done with great success two years in a row. But I had changed one of the variables and I knew that that must be the problem.
So I started looking more closely throughout the day and finally figured out what was happening: The water in the test tubes was evaporating, but instead of condensing outside the tubes and on the bags, it was condensing inside the test tubes! This meant that the water was just cycling within a very small space and was therefore difficult to detect. The reason was obvious: we didn’t have enough water in the tubes.
I came by the building on Saturday, after the Battle of the Books competition, and decided to try out my hypothesis. I increased the water level in my experiment and reset it so I could check it on Monday. It turns out my theory was correct! So I increased the water level in all of the arrays and resealed the bags. In just two days, we started to see progress! There were clouds of water forming on the outside of the bags and some droplets were beginning to drip down to the bottom.
I learned from the failed experiment and tried something new. This time it worked. I shared the results with the class and had them make further predictions about what would happen by next week. We also discussed what we saw happening and what evidence we had that evaporation, condensation, and precipitation were occurring. It was a great lesson that brought to life many of the concepts of the water cycle we have been learning. I am hoping that there will be even more dramatic effects to observe next week!