Why can fish float and sink?

In the vast waters, there are all kinds of fish. They swim in the water and float freely.

Fish are streamlined and suitable for swimming in the water. More importantly, its back is close to the lower part of the spine, and there is a bladder-shaped swim bladder filled with gas, which is the main regulating organ for fish to float up and down. Fish mainly adjust their position in the water by how much air is inflated in the swim bladder. The gas in the swim bladder is directly inhaled through the airway when it comes out of the water; The second is to absorb the gas dissolved in water through the red blood cells in the gill flap.

In addition, the fish's fins also play an important role, by shaking the muscles of the dorsal fin and the gluteal fin to maintain balance, so it can swim more stably in the water.

Most fish control their ups and downs by adjusting the gas in the swim bladder, but sharks are not like this. They don't have swim bladders, and if they don't swim, they will sink to the bottom of the sea. Some kinds of sharks solve this problem by inhaling air into their stomachs. When they sink, they burp and expel air from their stomachs. Some small sharks have large livers and contain a lot of hydrocarbon oil, which is lighter than water and can help snorkel.

Find an empty plastic bottle with a tight bottle mouth, poke a small hole in the bottle wall with nails, insert the rubber tube into the small hole, leave one end outside the bottle, and tie it tightly with nails and tape, thus making a submarine model.

What will happen to the model when the self-made "submarine" is immersed in water and inhaled from the pipeline? Blow into the pipe, what will happen to the model? Try it quickly, it's very interesting!