On Wednesday, Nov. 24, 2010, the Lower School Science Lab was full of activity as the 4th grade students and their grandparents and special friends visited for a very special hands-on, inquiry-based lab. The children and adults investigated the principles of buoyancy and density by making their own Cartesian divers. The diver is named after a French scientist and philosopher, Rene Descartes. The traditional Cartesian divers have been made out of glass medicine droppers or delicate glass ampules. The students used safe, plastic medicine droppers, or pipettes, weighted with a metal hex nut. When the students and grandparents properly adjusted the buoyancy, the diver would sink when pressure was applied to the outside of a 1 liter bottle, and would float when that pressure was released. The students noticed that the water level and air pocket size inside the diver changed when pressure was applied and released. Using the formula Density=Mass/Volume, the students could state that as more water entered the pipette, the mass changed, and the diver became less buoyant and sank. Then students realized that when the pressure outside the bottle was released, the compressed air inside the diver expanded (took up more space), and pushed some of the water back out. As the water level dropped inside the diver, it became more buoyant and floated to the top.
At the end of the lab, the students and grandparents/special friends were asked this question, "What would happen if we sealed the end of the diver with a drop of glue so no water could enter or leave the pipette? Would the diver still work?" I hope everyone puzzled over this during the Thanksgiving break. Maybe someone gave it a try while they were resting from eating all that turkey!
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