Classic cartesian divers always make one of the coolest science activities for kids! In this activity you’ll create your own cartesian diver using a pipette and learn how to make a transform your diver into squidy diver.

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I remember being so mesmerized by the cartesian diver science experiment when I was younger, so I was super excited to try this cool science activity with my group of first graders and second graders!

What is a Cartesian Diver?

If you’ve never seen a cartesian diver before, it’s basically a little dropper (or other material- there’s so many options) floating in a bottle of water. When you squeeze the bottle of water, the diver drops down through the water. It then floats back up when you release the sides of the bottle. It’s always fun to watch and seems magical! (This post contains affiliate links.)

How to Make a Cartesian Diver

There are tons of ways to make cartesian divers- from eye droppers to soy sauce packets! And you can even customize each one. In this activity I’ll be sharing one of the simplest ways to make cartesian divers using a pipette and hex nut. I’ll also show you how to turn your simple cartesian diver into a squidy cartesian diver!

Materials for Cartesian Diver

Empty plastic 1-liter or 2-liter bottle with a lid
Graduated pipette
Hex nut (Depending on the size of your pipette)
Scissors
Optional: Sharpies to decorate your bottle and dropper
Optional: To make a squiddy diver- electrical tape and disposable plastic glove

Directions for Making a Basic Cartesian Diver

1. Snip off the bottom of your pipette, leaving about 2 centimeters or so.

2. Slip a hex nut securely over the remaining portion of the pipette. (If the hex nut is too loose, you can secure it with some electrical tape.)

3. Fill your 1-liter or 2-liter bottle to the top with water.

4. Before putting your cartesian diver into your bottle of water, you’ll want to fine tune your diver’s density. To do this, take a small cup of water. Place the diver into the cup of water and squeeze the bulb to fill the pipette with some water. Let it go in the cup. You want it to just barely float. (If the diver sinks in your cup of water, squeeze out some water from the pipette until you get it to barely float.)

5. Once you’ve filled your pipette diver with water (and have a bubble of air inside the top), drop it into your large bottle of water. Screw the cap on securely. The cartesian diver should float in your bottle.

6. Squeeze the sides of your bottle. Your diver should go down. When you release the sides of the bottle, your diver should go back up! (Didn’t work? See troubleshooting below.)

7. Optional: Use colored Sharpies to decorate the outside of your bottle like an ocean. You can even draw a face right onto your diver.

Troubleshooting

If the density isn’t fine tuned just right, you might run into an issue of your diver sinking straight to the bottom or not going down when you squeeze the sides of your bottle. When this happens, it’s a great learning experience and challenge for the students to figure out!

With sunken divers we’d have to pour the water out of our bottle to get the divers out and then start over with adjusting our density bubble. (Usually the diver needed a bigger air bubble in the bulb.)

With floating divers that wouldn’t sink, we’d squeeze the sides of the bottle to get them to come out of the top opening so we could remove them and adjust their density. (Usually they’d need a little more water in the bulb of the pipette.)

Sometimes, it was easier to just start over. Many kids had more luck leaving a longer tail of the pipette on their diver.

How to Make a Squidy Cartesian Diver

You can challenge your kids to decorate their cartesian divers into all kinds of things- scuba divers, ballerinas, etc. using all kinds of materials! Here’s one way to transform your cartesian diver- into a squid!

1. Cut off the finger of a plastic glove (a thin balloon would probably work too). Cut off the top of the finger so you have a sleeve.

2. Use sharp scissors to cut some legs along the bottom of your sleeve.

3. Slip it over your cartesian diver (already made from a pipette and hex nut). Secure it with electrical tape (or other waterproof tape).

4. When testing out your squidy cartesian diver for correct density as described in the directions above, it can be harder to fill because of the legs. We used another pipette to squeeze water into our squidy and then tested him in a cup of water before putting him in the bottle.

5. Squeeze and release your bottle to make your squidy go up and down!

Extend Your Learning

Put more than one cartesian diver in your bottle at once- each with a different sized air bubble in the pipette. What happens?
Try your diver in both a 1-liter bottle and a 2-liter bottle. Do they both work the same?
Add appendages or other decorations to your diver using a hot glue gun and materials like foam sheets, pipe cleaners, string etc.
What happens if you fill your large bottle with half water and half oil? Does your diver work the same?