Submarine part 2

In science class, we worked on a simplified submarine. We used a water bottle, a balloon on a tube, water,  and washers.
So, how can a submarine be submerged, and float up again? A submarine uses a ballast tank to fill with air or air to control its buoyancy. When a submarine fills with water it sinks, making it negative buoyancy. When it fills with air, It will experience positive buoyancy.
To make our own miniature submarine, it took many attempts. We needed to record what we did right, and what we did wrong.
I made a chart of all the steps. The first part is labeled what we tried, and the second part is Next Steps.

Here are the different stages. Neutral Buoyancy, positive buoyancy, negative buoyancy. To make these stages possible, we needed to look at density, and mass. We needed enough mass for it to sink, but enough density to make it float. Our solution was to add a balloon into the bottle, and make a hole in the bottle to let water out.. We also added weights to balance out the bottle.

To make it sink, we needed it the bottle to be filled with water. But then, we needed it to have neutral buoyancy. To do that, we needed to balance out the weight of water, and air. We do that by blowing air in the balloon, but not too much that it floats up to the surface. We then blow the balloon the most it can go, and it floats up to the surface.

The pictures: