For day 19, my students completed their first (and one of my favorite!) practicum. This practicum is adapted from Flinn’s “Don’t Sink the Boat” activity. I gave students the challenge to float a plastic pill bottle as low as possible in the tank of water on my desk without letting it sink to the bottom by adding sand. Students had to use what they knew about density to add the correct amount of sand to keep the plastic container afloat. The goal was to get the density close to 1 g/mL but not over. This task was conceptually difficult for students at first, but once they understood the problem, they quickly rose to the challenge. I always issue an additional challenge to see which group can get the lowest sinking container.