Cartesian Diver

Cartesian Diver

Explore the science behind density and pressure with this DIY bottle diver. Make a scuba diver toy and watch it sink or float by  squeezing the bottle.

7 - 16
Est. Time:
<30 mins

How we did it:

Materials List

  1. two liter bottle - empty, plastic
  2. bendy straw
  3. small paper clip
  4. clay
  5. thick foil
  6. scissors
  7. water
  1. Draw a 1.5"x1" rectangle on your foil, and sketch out a basic diver shape within the rectangle.

    Cut out the diver

  2. Cut a 1.5" segment of the bendy portion of the straw.

  3. Use the paper clip to secure one end of the straw to the diver.

    Tip: It helps to bend the paperclip like the paperclip  on the right of the diver.

  4. Add on some clay on the diver's feet.

    Tip: Test your diver in a glass of water to make sure it floats in a vertical position. If the diver sinks, try removing some of the clay. If the diver lies flat horizontally, try adding some more clay.

  5. Fill your liter bottle top the top with water. Place the diver inside and make sure it floats.

    Tightly close the bottle.

  6. Squeeze the bottle to watch the diver sink towards the bottom!

    What's happening?

    When you place the diver in the bottle, air is trapped in the upside-down U shape of the straw. Squeezing the bottle causes the water to compress the air inside the straw. This makes the toy diver denser, which makes it to sink to the bottom. When the pressure is released, the diver floats back to the top!