Make a cartesian diver - Fun at-home activities for Kids.

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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.

Table of contents

Step-by-step guide to make a Cartesian diver

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The Cartesian Diver | Experiment & Explain | Bottle Diver Experiment | Air Pressure | Buoyancy

What you need

Plastic bottle with cap, water, small sealed eyedropper or small sealed plastic tube, modeling clay or putty, a cup or small bowl for testing, adult supervision required

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

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

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Here at SafeTube, we're on a mission to create a safer and more delightful internet. 😊

How to make a Cartesian Diver GAME | dArtofScience

4 Videos

Facts about buoyancy and pressure

🧪 The Cartesian diver is named after René Descartes and was described in the 1600s — it's a classic 17th-century science toy!

🔬 It shows Boyle's law: squeeze the bottle, the air bubble shrinks, the diver becomes denser and sinks.

🌊 Archimedes' principle explains the float — the diver rises when the water it displaces weighs more than the diver.

🧴 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.

⚡ Thanks to Pascal's law, pressure changes travel instantly through the water, so the diver responds right away when you squeeze.

How do you make a Cartesian diver at home to explore buoyancy?

Fill a clear plastic bottle almost to the top with water. Prepare a small sealed eyedropper or a tiny plastic tube with a little air inside so it barely floats. Drop the diver into the bottle and screw the cap on tightly. Squeeze the bottle to increase water pressure—the diver will sink; release and it will rise. Adjust the air in the diver (or add a tiny bit of clay) until it hovers before squeezing. Adult help recommended.

What materials do I need to make a Cartesian diver?

You need a clear plastic bottle with a tight-fitting cap, plain water, and a small sealed eyedropper or a short sealed plastic tube that can trap a bit of air. Optional items: modeling clay or Blu-Tack to fine-tune buoyancy, a funnel to fill the bottle, and towels for spills. Avoid glass and ensure small parts are sealed or supervised to prevent choking hazards.

What ages is the Cartesian diver activity suitable for?

This activity is great for children about 5–12 years old with adult supervision. Ages 5–7 will need close help with sealing, filling, and handling small parts. Ages 8–12 can do most steps independently but still benefit from an adult for safety checks. Not recommended for children under 3 due to small parts and water hazards. Adjust explanation complexity to the child’s age to keep it fun and educational.

What are the benefits, safety tips, and variations for a Cartesian diver experiment?

Benefits: teaches buoyancy, air pressure, scientific method, and encourages observation and problem-solving. Safety tips: use plastic bottles, supervise children, seal small parts, tighten the cap, and clean up spills promptly. Variations: try multiple divers, color the water with food coloring, experiment with different air volumes or temperatures, or attach tiny weights to compare sinking behavior. Keep experiments short and supervised for safe, hands-on learning.

Ready to create?

All Activities

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.

Table of contents

Step-by-step guide to make a Cartesian diver

0:00/0:00

Here at SafeTube, we're on a mission to create a safer and more delightful internet. 😊

The Cartesian Diver | Experiment & Explain | Bottle Diver Experiment | Air Pressure | Buoyancy

What you need

Plastic bottle with cap, water, small sealed eyedropper or small sealed plastic tube, modeling clay or putty, a cup or small bowl for testing, adult supervision required

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

Help!?

I can't find an eyedropper or modeling clay — what can I use instead?

My diver keeps sinking even before I squeeze the bottle; how do I fix it?

How can I adapt this activity for different ages?

How can we extend or personalize the Cartesian diver experiment?

Watch videos on how to make a Cartesian diver

0:00/0:00

Here at SafeTube, we're on a mission to create a safer and more delightful internet. 😊

How to make a Cartesian Diver GAME | dArtofScience

4 Videos

Facts about buoyancy and pressure

🧪 The Cartesian diver is named after René Descartes and was described in the 1600s — it's a classic 17th-century science toy!

🔬 It shows Boyle's law: squeeze the bottle, the air bubble shrinks, the diver becomes denser and sinks.

🌊 Archimedes' principle explains the float — the diver rises when the water it displaces weighs more than the diver.

🧴 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.

⚡ Thanks to Pascal's law, pressure changes travel instantly through the water, so the diver responds right away when you squeeze.