Hot Air Rises
Every so often the fourth graders take a break and do something fun. No grade involved. No test or assessment required. One week, we wrote a paragraph on all we could think of that might apply if we took a black bag of air out in the sunlight. Most of the class knew that black absorbs heat and that the air in the bag would get warm. That was a pretty good start.
We discussed molecules getting warm and moving faster and taking up more space. We talked about warm air rising, so the bag might float, and we discussed the difference between a demonstration and an experiment.
Then we took our black balloon bag out and filled it with air for our demonstration on warm air rising. Ours was a demonstration, not an experiment, because it had already been tested many times, and we knew what the results would be.
The fourth graders also pretended to be cold molecules (we just moved in place). Then we warmed up (a little more movement). And finally we became pretty warm (we moved around the area). Hopefully, this helped explain why the bag became fuller as the air warmed and then finally started to rise. Another comparison we used was a small piece of ice on a metal lid, then the ice warmed and melted on the lid, finally set in the sun, it evaporated. Wow, if it rained we would have had the water cycle.