According to the meaning of the question, the submersible sinks because gravity is greater than buoyancy. After the ballast iron is abandoned, the gravity of the submersible decreases, and when the gravity is less than the buoyancy, the submersible will float. It can be seen that the dragon realizes the ups and downs by changing its own gravity.

From the first contact with the water surface to immersion, the volume of submerged water, that is, the volume of discharged water, is increasing, indicating that buoyancy is related to the volume of discharged liquid.

The Jiaolong was completely submerged in the sinking process, and the depth increased, so did the water pressure, indicating that the liquid pressure was related to the depth.

So the answer is: self-gravity; Discharge a certain volume of liquid; The pressure of water; Liquid pressure.