Skip to main content

Novel Coronavirus — June 22, 2022 Update: Explore Scouts Canada’s actions as we continue to follow the direction of government and health agencies in maintaining public health. View recommendations and stay informed here. Learn more about Scouts Canada's new vaccination mandate.

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.

Back to Activity Finder


  • 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.