Observation is the key to conduct this experimental study of the Cartesian diver. First a 2-liter bottle is filled with water to almost all the way to the top, then prepare the diver which is a test tube, fill the test tube about 50-60% with water, place the diver inside the bottle the diver should float near the water surface then secure the cap on the bottle. When the container is squeezed, the diver should sink to the bottom of the container. Release the bottle slowly, the diver should come up in reverse order.
The Cartesian diver shows that air is compressible and water is incompressible. When the container is squeeze, the pressure from squeeze is distributed equal throughout the container and the volume of air in the diver decreases because of the increased pressure of the water surrounding the diver. Since the volume of air inside the diver decreased, and water filled up where the air use to be, the diver becomes denser and will begin to sink if enough pressure is applied. It begins to sink because it becomes denser so the upward force of the water is not great enough to keep the diver floating. When the container is not squeezed, the diver will float back to the top because the pressure that was compressing the air in the diver was relived so the air could take is normal volume again which make it least dense. Therefore the Cartesian diver does demonstrate the compressibility of a gas, the incompressibility of water.
The Cartesian diver experiment also demonstrates the Pascal 's law. According to Pascal 's law, when the bottle is squeezed, the applied pressure increase throughout the bottle by the same amount include inside of the diver. The