Straw Cartesian Diver

The best do-it-yourself Cartesian Diver using a straw, paperclip and a little creativity

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It just can’t get much more simple than this… a bendy straw and paperclip. As always, the key is to experiment with the materials you can find.

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How Does It Work

Squeezing the bottle causes the diver (the paperclip straw combo) to sink because the increased pressure forces water up into the open straw. The additional water increases the mass, and density, of the diver causing it to sink. Releasing the squeeze decreases the pressure on the air bubble at the top of the bent straw, and the water is forced back out of the diver, lowering its density and allowing it to float back to the top of the bottle.

Take It Further

What happens if you don’t fill the bottle completely to the top with water?

Can you make the diver work if the bottle is only filled 3/4 full?

Make three different straw divers – a small, medium and long-size diver using the same kind of straw and the same paperclip. The only difference will be the length of the straw. How does this affect the way the diver floats and sinks in the bottle?

After lots of experimenting, find the “perfect” diver – the one that floats and sinks the best. Bend the paperclip into the shape of a “hook” to try to pick up items on the bottom of the bottle. You’ll need to make some “sunken treasures” that sit at the bottom of the bottle with a loop of wire help facilitate the rescue. Watch the video on Cartesian Diver Toys to get some ideas.


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