What does a submarine do to get up and down by changing itself? Submarines rise and sink by changing their own gravity. In water, submarines are subjected to buoyancy and gravity. _F float = P water V row g, the volume of submarine remains unchanged, and the volume of discharged water remains unchanged. _Submarine buoyancy remains unchanged when subjected to water; Compressed air is pressed into the pressure chamber of the submarine, and the sea water is discharged. The weight G of the submarine decreases. When F floats > G, the submarine floats. Open the valve of the pressure chamber and let the sea water enter the pressure chamber. The submarine's weight G increases. When F floats below G, the submarine sinks. When F floats = G, the submarine is suspended and can stay at any depth. Thus, submarines can rise and sink by changing their own gravity.