Why do cartesian divers sink

Cartesian divers are a quick and simple way to illustrate relationships among pressure, volume, temperature, and buoyancy. The Activity could be used in connection with the concepts of gases and liquids and discussions of Boyle's, Charles's, and the ideal gas laws. A biological application is that some fish have a small sac containing an air bubble inside their bodies. They control the size of the sac to alter their buoyancy in the water. The optional extension could be a chemistry recruitment exercise or a year-end engineering project with considerable room for student inventiveness.

View Author Information. Cite this: J. Article Views Altmetric -. Citations 2. Abstract Cartesian divers rise and sink in water that fills a capped bottle when there are changes in pressure, volume, temperature, and buoyancy. Cited By. This article is cited by 2 publications.

When you squeeze the sides of the bottle, you are increasing the pressure on the liquid inside. That increase in pressure is transmitted to every part of the liquid. That means you are also increasing pressure on the eye dropper itself. Squeeze hard enough and you will push some more water up inside the dropper. The air inside the dropper squeezes tighter as more water is forced in.

Now, water is much denser than air. So when you push more water inside the dropper, you increase its overall density. Once its density is greater than that of its surroundings, it will sink. Release the pressure on the bottle's sides and you stop forcing water inside the eye- dropper. Water is incompressible, but air is not.

When you exert pressure on the bottle, not only do you compress any air in the bottle, but you raise the pressure throughout the water. For the open diver, this forces water into the bottom of the diver, compressing the air inside the top of the diver. With the additional water, the diver is now denser than it was before, and it weighs more than the water it displaces. In other words, its weight now exceeds the buoyant force on it, and the diver sinks to the bottom. For the closed diver, the increased external pressure compresses the diver, which has a flexible wall.