Cartesian Diver

Our Cartesian Diver was not the fastest, but it worked. It was always positively buoyant, until we squeezed the bottle. When we did water filled it up and the air pocket got smaller, which made it negatively buoyant and forced it to go to the bottom. Since it was already positively buoyant, the mass or the weight was light because air is lighter than water. When we pressed against the bottle, water, which was the ballast filled up and most of the air went out so, the mass got heavier, which made it sink. However it never got neutrally buoyant on its own. We had to squeeze it and if it was ever neutrally buoyant, it was for a very short amount of time. The volume especially changed because when the diver was filling up with water the inside got heaver and changed it. The density changed the most because since the mass and the volume changed the density got heavier all because of the ballast or the water.