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Cartesian Diver

Name of Corresponding Unit Plan: Aquatic Environment

Grade Level: 5-12

Common Core Standards:
RS. 3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.

Content Areas: Science

Recommended Length/Duration: 45-60 minutes

Learning Goals: Students will observe the effects of pressure on a closed system.


  1. Discuss buoyancy and why things float or sink.  Point out that most objects have fixed characteristics that determine their buoyancy.  However, in this experiment students will be building a devise whose buoyancy they can control.
  2. There are several options for the construction of a diver.  They can be made from glass eyedroppers, drinking straws, plastic tubing, glass or plastic vials.  The key is to make sure there is just enough air in the tube to enable it to float upright just at the surface of the water.
  3. A clear plastic soda bottle should be filled with water leaving a little air at the top. 
  4. Place the diver into the bottle and seal the bottle with its cap.
  5. If you squeeze the bottle, the diver should sink.  When you release the bottle the diver should rise again to the surface.  If the diver doesn’t sink, have students add a little more water or weight to the tube so that it will float just below the surface.
  6. Have students practice controlling the rate of decent and assent.  Have them see if they can hold the diver’s position at different depths.
  7. As students to explain how this happens.  Guiding questions might include:
    • How does squeezing the bottle affect the diver inside?
    • What changes as the bottle is squeezed?
    • Can you see a change?
    • How does pressure to the bottle transfer to the air?
  8. Your discussion should include the concept of pressure.  When the bottle is squeezed you are adding mechanical pressure to reduce the size of the bottle.  The water inside the bottle cannot be compressed, but the air can.  If they have not noticed how the air space gets smaller, have then experiment to observe this.  Point out that not only does the air at the top of bottle compress, but so does the air in the tube.  If they have not observed this, have them do so.  Point out that when air is compressed it becomes more dense, takes up less volume, and decreases the buoyancy of the diver. 
  9. Ask where compressed air is used in everyday activities.

Assessments: Informal assessment based on participation and effort.

Materials/Resources: Cartesian Diver Experiment Sheet (pdf), Large, clear plastic soda bottles with caps, eyedroppers or other materials to construct divers, water.

Special Considerations: There are many different ways to construct the divers.  The teacher will have to decide what materials they have available and will need to prepare them in advance.  Safety precautions should be taken if students will need cut materials to fashion their diver.

Extensions: Students may want to do a mini research project on Archimedes Principle.

There are many ways to “dress up” their diver to make it more interesting.  There are also several YouTube videos available to explain and extend the activity.  A few examples are:

Make a Cartesian Diver

Diving Katsup Packet

Steve Spangler Science