Cartesian Divers

A Cartesian Diver is a classic rising and sinking toy that uses the principles of buoyancy, density, and Boyle’s Law. Squeezing the bottle will cause the diver to sink due to the added pressure causing the air in the diver to compress. There are two versions of this toy: open and closed.

The open diver has an opening that holds a bubble of air that allows water to be pushed inside when pressure is applied on the outside of the bottle. The diver is able to float because the mass of the air within the volume of the diver gives the diver a lower density than water. When the pressure is applied this decreases the bouncy because the air is pushed into a smaller area at the top of the diver and allows for more water to enter which increases the diver’s mass even more meaning it will sink.

The closed diver is a completely closed packet that contains air, but the diver is also able to bend and compress due to the material it is made of. The diver is able to sink because the air inside the diver becomes compressed from the outside pressure. The pressure makers a smaller bubble of air inside that in turn decreases the overall volume of the diver, lowering the density, and causing the diver to sink.

Key Terms

Mass – is a measure of the amount of matter in an object

Volume – the amount of space occupied by the observed matter

Density – the degree of compactness of a substance; the quantity of mass in a given volume; Mass divided by Volume

Buoyancy – the ability or tendency to float in a fluid

Pressure – the amount of force on a until of area

Float – to rest or move on/near the surface of a fluid

Sink – to go below the surface of a fluid

Boyle’s Law – the pressure of a gas will increase as the volume decreases, if the gas is at a constant temperature.

Supplies:

Flexible Clear Plastic Bottle with Cap (Can be a 2-Liter, Water Bottle, Soda Bottle, Etc.)
Water
Food Coloring* (*Optional)

Open Diver Model #1
Paperclips
Straight Plastic Straw Not
Scissors

Open Diver Model #2
Paperclips
Bendy Plastic Straw

Scissors

Open Diver Model #3
Pen Cap
Tape
Paperclips OR Playdoh

Closed Diver Model
Condiment Packet (Ketchup Packet, Soy Sauce Packet, etc.)