Science Under Pressure

As part of their larger ocean science unit, fifth graders have been using the engineering design process to create and test Cartesian diver systems. Through hands-on experimentation, students explored how density and pressure interact to affect buoyancy—key concepts for understanding how objects move in water.

Students started by assembling their diver system: a small tube partially filled with air and water, submerged inside a sealed, water-filled soda bottle. Their first challenge was to achieve neutral buoyancy - carefully adjusting the balance of air and water so the diver would float just below the surface rather than sinking or rising too quickly. “It’s a tricky balance,” noted science teacher Cecilia Owens, as she circulated the classroom helping students refine their designs. With each adjustment, students tested and redesigned their divers, observing how adding water and reducing air increased the diver’s density. By squeezing the bottle, students increased the pressure inside, compressing the air in the diver and changing its buoyancy. Depending on the amount of pressure applied, the diver could sink quickly to the bottom, rise quickly to the surface, move more slowly in either direction, or hover in the middle of the bottle.

Throughout their experiments, students recorded their own observations and questions, using the concepts of density, mass, and volume to explain the movement of their Cartesian divers, and to consider whether the diver’s mass or volume actually changed during each trial.  Building on this, students extended their ocean studies by designing original sea creatures adapted to specific ocean zones. Each design reflected an understanding of environmental conditions, necessary adaptations, and potential predators, allowing students to apply core science concepts in creative ways.