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.

Step-by-step tutorial

  • Step 1

    Draw a 1.5"x1" rectangle on your foil, and sketch out a basic diver shape within the rectangle. Cut out the diver

    Photo reference of how to complete step 1

  • Step 2

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

    Photo reference of how to complete step 2

  • Step 3

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

    Photo reference of how to complete step 3

  • Tip

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

  • Step 4

    Add on some clay on the diver's feet. If the diver sinks, try removing some of the clay. If the diver lies flat horizontally, try adding some more clay.

    Photo reference of how to complete step 4

  • Tip

    Test your diver in a glass of water to make sure it floats in a vertical position.

  • Step 5

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

    Photo reference of how to complete step 5

  • Done!

    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 sink to the bottom. When the pressure is released, the diver floats back to the top!

    Photo reference of how to complete step 6

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