The sixth graders have been studying density in science class. After learning about the abstract concept, students worked in groups to study and analyze three fun applications of density's impact on the sinking and floating of everyday objects and people. We used a "Predict. Observe. Explain" structure to keep track of what was happening and to begin to piece together a rich explanation of why it was happening. In one experiment, students built "lava lamps." A bottle filled with oil and a little colored water is ordinary, but add an alka seltzer tablet to create some carbon dioxide and all of a sudden you get bubbles rising and falling. The gas gets trapped in a water bubble making it less dense than oil and causing it to rise. When the bubble pops at the top, all that is left is water, which sinks back down, and the process repeats. A similar thing happens to some beans in vinegar when you add baking soda. The gas creates mini life jackets for the beans, making them less dense by increasing their volume without adding much mass. Perhaps, most interestingly though, we investigated why we float so easily in the Dead Sea. When salt dissolves in water, it makes the water more dense, making humans (or, in our model, some boiled eggs dubbed Eggbert/Eggbertina) relatively less dense. It was magical to see the egg float in the middle of the glass - right between the fresh water and the very-salty water! It was even more magical to hear students comfortably use their scientific knowledge to explain what they have seen and experienced, and to begin to see other everyday occurrences in new ways. Consult your local sixth grader to try these demonstrations at home!
