Things you'll need:
Aug 10, 2012
Science Toys: Cartesian Devil
There are a couple of ways I am like an elf - not the archery or magical spells kind, I mean elf as in little guy in pointy shoes works in the North Pole variety. I like to do things that make kids happy, and I love to make toys (I'm also adorably short at 5'0", tiny, just like a real elf)! My favorite toys to make are the kind I can dig through my crafts and recycling drawers to find the materials for, and the kind that teach something amazing in a simple way. I'm slowly but steadily building up my personal collection of homemade science toys that demonstrate all sorts of things like molecular polarity, cyclone formations, air pressure... the list goes on! About a year ago, I made up one of my first ever science toys, the Cartesian Devil. This is a nifty little thing that demonstrates Archimedes' Principle about how pressure relates to the buoyancy of an object. It's also super simple to whip up at home with 4 common materials. I had to make myself another one after my original one made its permanent home at the museum.
First, make your devil. Bend your straw in half so that the two ends meet.
If it floats to the top on its side, it's too buoyant, and needs to be heavier - add some paperclips. Also, if it sinks to its side, the devil is probably off balance, try wrapping the rubberband closer to the ends and further from the bent part. You might need to start over with a new straw if yours gets too mangled.
The sweet spot is when it floats, but only the tip of the bent part is out of the water and the rest of the diver hangs straight down in the water. This is neutral buoyancy and it's perfect.
Fill the soda bottle all the way to the brim with water. Then put the devil into the bottle, paperclips first. Do this over the sink, the devil will displace and spill some water while it goes in. The devil should hang just at the top of the water line in the bottle just like it did in the tall container. Seal the bottle really tight with its cap.