Cartesian Diver Density & Buoyancy Submarine
An engaging, screen-free learning activity that builds real-world creativity and critical thinking for kids aged 7 to 9.
Materials Needed
- • 1-liter or 2-liter clear plastic bottle with cap (1 unit)
- • Flexible plastic drinking straw (1 unit)
- • Small metal paperclips (3–4 units)
- • Water (1 bottle full)
Pro Tips
- → Tune the diver in a cup of water before placing it in the bottle: it should just barely float with only the tip breaking the surface.
- → Explain that squeezing the bottle increases pressure throughout the liquid, compressing the air bubble inside the straw and making the diver sink.
- → Releasing grip pressure allows the air bubble to expand, restoring positive buoyancy.
Safety First
Ensure the plastic bottle has no cracks; screw the cap on tightly to prevent leaks when squeezed.
How was this activity?
Your anonymous feedback helps us recommend better activities.
Step-by-Step Instructions
Step 1
Cut the flexible bendy section of a plastic straw with 2 cm of tail on each side and fold it into a hairpin shape.
Step 2
Slide two metal paperclips onto the ends of the straw legs to serve as a ballast weight and keep the straw folded.
Step 3
Test the diver in a glass of water, adding or removing paperclips until it floats upright with its tip barely breaking the surface.
Step 4
Drop the diver into a bottle filled to the brim with water, seal the cap tightly, and squeeze the sides to dive and ascend at will.