Swimming Squid (Cartesian Diver)

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 s