First of all, since the 'diver' needs to go up and down while upright, we had to first make it upright. To do this we filled the 'diver' with water with the whole dropper acting as a ballast tank and the water acting as a ballast. This way the diver would have enough mass to float upright in the water, but not enough to sink. At this point, the 'diver' has a positive buoyancy, or floating, which is caused by having a volume greater than it's mass. This way its density is less than water, which has an average density of 1 g/cm3.
Now you squeeze the water bottle which will cause the dropper to fill up with even more water. With the increase in mass it will start to sink, thus giving it negative buoyancy. To have a negative buoyancy, or sink, the mass will have to be greater than the volume, which also means you have a higher density than water.
Now it is also possible to have a neutral buoyancy, which means the 'diver' will stay in the middle, not floating nor sinking. To do this you cannot squeeze the bottle to hard. You must squeeze the water bottle just the right amount so that its mass is equal to its volume and its density is pretty much equal to the water around it. This way the 'diver' will hover in the middle of the water bottle.
This is how a Cartesian Diver, a classic science experiment works. We can all give credit to Rene Descartes for discovering the principle of buoyancy and making the experiment.
Now it is also possible to have a neutral buoyancy, which means the 'diver' will stay in the middle, not floating nor sinking. To do this you cannot squeeze the bottle to hard. You must squeeze the water bottle just the right amount so that its mass is equal to its volume and its density is pretty much equal to the water around it. This way the 'diver' will hover in the middle of the water bottle.
This is how a Cartesian Diver, a classic science experiment works. We can all give credit to Rene Descartes for discovering the principle of buoyancy and making the experiment.
