Cartesian Diver

A **Cartesian diver** is specially made by blowing a small glass tube with a little water inside (or you can just simply use a dropper). When we put the diver into a tall closed plastic bottle with water upright we can achieve a **balance with the diver floating on the surface of the water**. The diver rises or sinks depending on its density. ***When its overall density (glass tube and air), is less than that of water it will float and when its overall density (glass and air) is greater than that of water it will sink***. If the bottle is squeezed hard enough the density of the diver will increase (the compressible air inside will lower its volume due to the pressure from outside) until it is greater than the density of water and thus it will sink.