Cartesian Diver (Audrey Benson)

Author

Audrey Benson from Moorpark High School.

Principles

Demonstrates buoyancy, the ideal gas law, and Pascal's principle. Squeezing on the top of the sealed container decreases the volume and therefore increases air pressure above the water.

Standards

Include the science standards which are addressed by this equipment. If no specific content stards are addressed, use the investigation and experimentation standards.

Materials needed

Cartesian Diver kit:

• Glass cynlinder

• Small glass floater

• Cloth

• Rubber Bands

• Water

Procedure

• Fill cylinder with water

• Place glass floater inside

• Cover with cloth and secure with rubber band

• Press on secured cloth to watch glass floater rise and fall

Explanation

Squeezing on the top of the sealed glass container decreases the volume and therefore increases air pressure above the water. By Pascal's principle, that pressure is transmitted to all parts of the container. This increases the pressure inside the small glass vial. The increased pressure decreases the volume of air at the top of the vial, and in so doing, decreases the amount of water displaced by the vial. This decreases the buoyant force on it enough to cause it to sink.

Questions

1. Why must the container be completely filled with water and sealed?

The water must be all the way at the top, touching the cloth so that when you press down, some of the water comes out and the volume of the container is decreased.

2. Why does the diver move when you press on the cloth?

Because the volume of the container is decreased and water is displaced, the buoyant force decreases and causes the diver to sink.

3. Why does the diver rise when you let go of the cloth?

The volume increases again and the buoyant force causes the diver to rise.

Everyday examples of the principles illustrated