Density Experiment

The last two weeks have been sort of like the ending to a movie. In Mr. Sowder’s class, the students have transitioned from learning physical science to earth science. The overall objective of the last unit of the semester is to help the students discover why the earth is shaped the way it is and why various formations exist on the earth’s surface. The students spent time plotting marks on a globe that represented earthquakes and volcano eruptions over the last 30 years. Mr. Sowder and I decided that I would lead a lab demonstration that explained the process of convective currents. Mr. Sowder would then take the information about convective currents and connect it with the theory of plate tectonics.

This assignment was perhaps my greatest challenge of the year. Earlier I had done presentations on college, or lectures on electricity, but I’d yet to lead a full-fledge lab. Furthermore, I was not entirely familiar with convective currents or plate tectonics. I know that this project would require a significant amount of research on my part. To make a long story short, I used several websites to get a food understanding of these concepts. Then, I found a few good activities that the class could do. From there, I constructed my lesson plan and crossed my fingers.

Mr. Sowder gave me two days to complete the lesson plan and I agreed to come in and do the lesson for his second hour (in addition to the fourth hour class which I normally visit). After researching convection currents, I thought it would be important to the students to have an understanding of density first. I began the lecture by explaining the terms mass, volume and density and showing how they were related. We did a few examples, but I wasn’t completely sure how well the class understood the concept. To explore density a little bit more, I began to do some demonstrations. I filled three cups with water, 91% rubbing alcohol, and vegetable oil. We then observed what happened when we put ice, wood, and aluminum in each cup. Much to the surprise of the class, the ice sank in the rubbing alcohol and kind of sank in the vegetable oil. The wood floated in all three and the aluminum sank in all three. Based of these observations and a table of densities, we walked through the steps of understanding that lower density materials float whereas higher density materials sink. The students absolutely loved this part of the class. They were very interested in seeing what would happen with the different solids in each fluid. I don’t think any students had seen ice sink before and I felt that was the key part to get them hooked on the day’s activity.

After establishing the basic concept of density, I asked the class to predict what would happen if we mixed alcohol, vegetable oil ad rubbing alcohol. Through lots of guessing, we made a prediction using the known densities of each species. I added food coloring to the rubbing alcohol in order to make it distinguishable from the water. The experiment worked nicely and the students were pleased to see their predictions come true.

Tune in next time to hear how the second day worked with the convective currents experiment.