wikiHow to Make a Spinning Cartesian Diver

With this variation of the Cartesian diver, you can put two of them in the same bottle and they'll spin in synchrony like little underwater dancers! This Cartesian diver can also demonstrate the principle of buoyancy (Archimedes’ principle) and the ideal gas law.[1]


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    Bend a straw into a "J" shape.
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    Cut the straw so that the length of the left and right is same.
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    Insert the straw through the washer so that the washer rests on the bendy part.
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    Pinch the ends together with pliers.
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    Hold up a flame to the ends so that they are sealed together.
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    Make two holes with a pin, as shown in the images.
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    Drop the straw into a glass of water.
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    Adjust the buoyancy by squeezing it so that the straw sucks up water through the pin holes. That'll make it sink a little. You want it so that about 5-10mm of the straw is barely above the water.
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    Repeat all of these steps to make a second Cartesian diver.
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    Put both divers in a bottle of water.
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    Screw on the bottle cap tightly. The seal must be airtight.
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    Grasp a bottle and experiment with squeezing it and loosening your grip. When this movement is repeated, the straws will spin as they go up and down.


  • Squeezing the bottle compresses the air in the diver and also pushes a little water into the pinholes. When the bottle is released, the air in the diver expands and some of the water is expelled. The diver floats again (because it is now less dense since the air within has expanded) and the straw spins because water is expelled through the pinholes on either side, just as a rocket ship moves by expelling burning fuel.
  • This is a great activity for older people to share with young ones.


  • Always practice safety precautions. be careful with scissors and lighters.
  • If the washer is too heavy, then the straws will simply sink to the bottom.

Things You'll Need

  • Flex straws
  • straws and a washer
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    Washers (stainless)
  • Pair of scissors
  • Radio pliers
  • Lighter
  • Marking pin
  • Glass of water
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    Plastic bottle