Virginia Tech - Invent the Future

Cartesian Divers Project

Supplies Provided By Us

  • Large Cups (about 20oz)
  • Pen Caps
  • Clay
  • Paper Towels

Supplies To Be Provided By Requestor

  • 20oz Soda bottles with their lids
  • Water

Subjects Covered

  • Bouyancy
  • Forces
  • Pressure

Description and Procedure

The Cartesian Diver demonstrates the principles of bouyancy and equal forces. To create the diver, the students must find a way to balance the buoyant force from the trapped air in a pen cap, and the force of gravity from the weight. The students add clay to the pen cap to give it more mass and seal the holes at the top of the cap. To test to see if the diver is correctly balanced before putting it in the bottle, have the students place it in the large cup of water and push it below the surface gently. The diver should just barely float. If it sinks to the bottom, some clay must be removed. If the diver floats up very quickly, more clay should be added to the bottom of the cap. Once the divers are balanced, the 20oz bottles should be filled completely with water and the cap should be gently placed in. As the diver is being inserted, some water will spill out, so this part is best done over a tub, sink, or paper towels. Care should be taken to prevent the cap from losing its air while being inserted. Once the diver is inside, screw the cap on the bottle and squeeze the sides. If it is filled enough, and the diver balanced correctly, with a small squeeze of the bottle the diver should sink. When squeezed, the pressure inside the bottle forces water into the cap making it heavier and sink. When the pressure is released, the air in the diver forces the water out and the diver rises again. Once completed, the student has its own "squidy" to take home.