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Cartesian Diver

Buoyancy is a measure of how well something floats (or not!) Build a Cartesian Diver in a bottle to explore how water and air pressure can affect your ability to float.

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  • What do you know about water pressure? Air pressure?
  • What do you know about buoyancy?
  • What will you use to build your diver?


  • Clean any labels off your pop bottle so you can see what is happening.
  • Build your diver so that it floats vertically just below the surface of the water.
    • There are a few ways to build your diver. One way is to attach a small piece of modeling clay to the end of a pen cap. There should be just enough clay that the pen cap floats just below the surface of the water.
    • What other methods can you use to build your diver?
  • Fill your empty bottle with water.
  • Drop the diver into the bottle and screw the lid on tight.
  • Give your bottle a squeeze. What happens?
  • Control the motion of the diver by squeezing and releasing the bottle, forcing the diver to move up or down


  • What do you know now that you did not know before?
  • What happened to the diver when you squeezed the bottle? When you let go?
  • What forces are acting on the diver?
  • What do you think would happen if the diver was less heavy?
  • How do you think this relates to a scuba diver?
  • What elements of STEM are in this adventure? Science? Technology? Engineering? Mathematics?
  • What did you like about this adventure? What did you not like?
  • How would you do this adventure differently?
  • Remember to submit your activities on our Scouts for Sustainability Take Action Map to the Review section.


  • 1 litre pop bottle and lid
  • 5 mL eyedropper
  • Something to use to make a diver, such as:
    • An eyedropper
    • A plastic pipette and a metal nut
    • A pen cap with no hole and some modelling clay

Keep it Simple

  • Try other things to see if they float. Try a stone, a feather, a bean etc.

Take it Further

  • How does buoyancy work in submarines? Learn about how submarines work.