Something I discovered as a kid in a science experiment book was called a “Cartesian Diver.” It consisted of the top end of a bendy straw, a rubber band, and some paper clips. After assembling those parts into a “diver,” you drop it into a bottle of water full to the brim and put on the cap. The straw would trap an air pocket that would make the “diver” float. When the bottle is squeezed, the air inside is compressed, and water is able to enter the straw and make the diver more dense, making it sink. When the bottle is released, the “diver” returns to the top of the bottle. 

It is a fun experiment that demonstrates Archimedes’ principle of fluid displacement and buoyancy. Essentially, an object in water displaces fluid equal to the object’s volume. If the amount of water displaced by the object is more dense than the object itself, the object floats. If the water is less dense than the object, the object sinks. It is this principle that is used to make sure that extremely large, heavy ships can still float on water. This is a small scale demonstration of this principle. (Link here to Wiki article on Cartesian Divers: [https://en.wikipedia.org/wiki/Cartesian_diver](https://en.wikipedia.org/wiki/Cartesian_diver))

3D printing takes the experiment to the next level. Not only can I have a diver that functions as it should, but it can look cool too! I wanted to make something that would make sense to be in water (like a sea creature) and also be fun and attention grabbing.

Presenting the “Swimming Squid!” 

As an homage to the original bendy-straw diver, I wanted to incorporate paper clips into this diver - and so “Squidward” (as my son calls it) uses a single mini colored paper clip (unfolded) as his tentacles. See the picture for how I folded mine. You will need to straighten the clip out, then fold it in half. If you leave the middle of the fold wide enough, it will require a little force to get it to “pop” into the bottom of the squid, but once it is in, it should stay. I used a pair of pliers to add some folds to the very ends of the clip to make “feet” on the end of the tentacles. Be creative and experiment with what shape you like best.

I used 100% infill for the eyes and the body. Make sure you do too (my profile uses this setting). Having the right mass for the squid is important or it may not work right.  A little dot of super glue will hold the body and eyes together.

Should fit in any ordinary sized soda bottle. Make sure to fill the bottle all the way up to the brim and then place your tentacled friend inside to make sure the bottle is as full as possible. Any air gaps inside can interfere with the distribution of water and pressure.

P.S. Adding a little food coloring to the water can make it extra fun for little kids! Not just for kids though - even as an adult I’m having a blast 🙂