It’s a magic trick of shifting gravity and repulsion. Any object in water that, in addition to being subjected to a force in the vertical downward direction, is also subject to the upward force of the water. That upward force is the thrust.
When the thrust is greater than gravity, the object will float to the surface, when the thrust is less than gravity, the object will sink, when the thrust is equal to gravity or the difference is very little, the object will “float” in any location in the country.
If the difference between gravity and thrust of the submarine is adjusted, it can sink, float. But the submarine’s hull is fixed and does not change, so the thrust it can withstand in the water is unchanged.
When repulsion is greater than gravity, the object will float to the surface.
Therefore, wanting to adjust this difference can only be done by changing the weight of the ship itself.
Submarine designers have designed the submarine as a hull consisting of two inner and outer shells. In the space between the inner shell and the outer shell divided into a number of water chambers. Each water tank is equipped with water inlet and outlet valves.
A submarine floating on the water wants to dive, just open the valve to bring water into the water tanks to let the sea water quickly fill, then the weight of the submarine increases and when the weight exceeds the thrust, The ship will sink.
If the submarine is diving underwater and wants to surface, it only needs to use the inlet valve and then use compressed air with extremely high pressure to spray water in the water storage compartments through the discharge valve to flow out.
At that time, the weight decreased, the thrust of the submarine was greater than the gravity, so the ship floated out of the water. If the submarine wants to run in the water between the sea surface and the seabed, it can put water in part of the water tank.
Or the submarine discharges part of the water in the water tank to regulate the weight of the submarine equal to or slightly greater than the thrust. At that time, submarines can go in areas of water of different depths and shallows.