Experiment

1. Using the permanent marker, number the pipettes “1” through “5.”
2. Screw a hex nut onto one of the pipettes.
3. Cut the pipette just below the hex nut.
4. Repeat steps 2 and 3 with the remaining pipettes and fill a drinking glass with water.
5. Squeeze the pipette to draw in or release water until the pipette BARELY floats in the drinking glass. Repeat with the remaining pipettes.
6. Place pipette “1” in the bottle (full to the rounded portion with water).
7. Squeeze 3 drops out of the pipette “2” and place it in the bottle. Squeeze 6 drops out of pipette “3,” 9 drops out of “4,” and 12 drops should be squeezed out of pipette “5.”
8. Fill the remainder of the bottle with water and screw the cap on tight.
9. Squeeze the bottle and watch the divers sink, one at a time. Release your grip and you’ll see the diver float right back to the top… one at a time!

Note: If the bottle requires a super-strong squeeze to move the divers, there isn’t enough water in the pipettes. Remove the divers from the bottle and increase the water levels in the pipettes so they just barely float.

How Does It Work?

The Cartesian Diver is a classic science experiment that’s hundreds of years old. It’s named for a Frenchman, René Descartes (1596-1650), who made huge contributions in the fields of philosophy, math, and science. The original Cartesian Divers were made out of glass medicine droppers or delicate glass ampules. When you have the water levels adjusted correctly in your new, unbreakable divers, you should see the water in the diver rise as you squeeze the bottle. The air trapped in the pipette compresses into a smaller space and the diver’s weight increases. It becomes less buoyant and it sinks. When you release the squeeze, the compressed air expands and forces water out of the diver, allowing it to float to the top of the bottle.

So, why do they sink one by one, and float similarly? It has to do with the drops of water you squeezed out before tossing your divers in the bottle. Keeping in mind how the divers work, each one reaches its buoyancy threshold with a different amount of pressure on the bottle.