Make a cartesian diver
Make a Cartesian diver using a plastic bottle, water, and a small sealed tube or eyedropper to explore buoyancy and pressure changes safely at home.
Step-by-step guide to make a Cartesian diver
How to make a Cartesian Diver GAME | dArtofScience
Step 1
Ask an adult to help you with this experiment.
Step 2
Put all your materials on a flat table where you can work.
Step 3
Rinse the plastic bottle and cap so they are clean.
Step 4
Fill the bottle almost to the top with water leaving about 1 inch (2 cm) of air at the top.
Step 5
Squeeze the eyedropper to push most of the air out.
Step 6
Place the eyedropper upright into the cup of water so it fills partly and floats.
Step 7
Pinch off a very small piece of modeling clay and press it onto the bottom of the eyedropper.
Step 8
Put the eyedropper back in the cup to see if it barely floats with the tip dipping into the water.
Step 9
Add tiny more bits of clay or remove a bit until the eyedropper just barely floats with its tip under the water.
Step 10
Carefully lift the prepared diver and drop it into the nearly full bottle.
Step 11
Screw the cap on the bottle tightly so no water leaks.
Step 12
Squeeze the sides of the bottle firmly to watch the diver sink and then release the bottle to watch it float back up.
Step 13
Share your finished Cartesian diver on DIY.org
Final steps
You're almost there! Complete all the steps, bring your creation to life, post it, and conquer the challenge!
Help!?
I can't find an eyedropper or modeling clay — what can I use instead?
Use a small medicine syringe without a needle or a clean travel dropper instead of the eyedropper, and substitute play‑dough, Blu‑Tack, or a tiny wrapped ball of aluminum foil for the modeling clay to add weight as in the 'pinch off a very small piece of modeling clay' step.
My diver keeps sinking even before I squeeze the bottle; how do I fix it?
Lift the prepared diver back into the cup and remove tiny bits of clay or push a little more air into the eyedropper (undo the 'squeeze the eyedropper to push most of the air out' action) until it just barely floats with its tip under the water before putting it into the nearly full bottle.
How can I adapt this activity for different ages?
For younger children have an adult rinse the bottle, fill it nearly to the top, and attach the clay while the child watches and squeezes the bottle, whereas older kids can experiment by changing clay amounts, using different droppers, and recording how buoyancy changes.
How can we extend or personalize the Cartesian diver experiment?
Make several divers with different clay weights or droppers, color the water, and compare how much squeezing is needed to sink each diver while timing or measuring the depth to create a simple data chart of results.
Watch videos on how to make a Cartesian diver
Density and the Cartesian Diver
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Density and the Cartesian Diver
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Facts about buoyancy and pressure
⚡ Thanks to Pascal's law, pressure changes travel instantly through the water, so the diver responds right away when you squeeze.
🌊 Archimedes' principle explains the float — the diver rises when the water it displaces weighs more than the diver.
🔬 It shows Boyle's law: squeeze the bottle, the air bubble shrinks, the diver becomes denser and sinks.
🧪 The Cartesian diver is named after René Descartes and was described in the 1600s — it's a classic 17th-century science toy!
🧴 You can make a working diver with just a plastic bottle and an eyedropper, a pen cap, or a small sealed tube — no special kit needed.
How do you make a Cartesian diver at home to explore buoyancy?
What materials do I need to make a Cartesian diver?
What ages is the Cartesian diver activity suitable for?
What are the benefits, safety tips, and variations for a Cartesian diver experiment?
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