In this blog post, we will look at the principle of how submarines rise or sink in water through buoyancy control and how that principle resembles other phenomena in nature.
If you put a rubber duck in a bathtub, it will float back up to the surface. However, if you put our body in a bathtub, it will sink to the bottom. In this way, objects either float to the surface or sink to the bottom when they enter water. However, there are objects that can sink under water and then float back up to the surface depending on the situation. It is a submarine. Submarines can adjust the depth they are submerged in underwater without using the power of an engine. How can submarines adjust their depth underwater?
First, let’s find out the difference between objects that float and objects that sink. To understand the principle of submarines, we need to take a brief look at the history of submarines. The first submarine is said to have been built by the 17th-century Dutch inventor Cornelius Drebbel. His submarine was a small wooden vessel that simply moved through the water using human power, but over the following centuries, submarines developed into complex machines for military purposes. At the heart of this development was an understanding of buoyancy and gravity.
Gravity acts equally on objects submerged in water. However, since objects floating on the surface of the water are stationary, we can see that the magnitude of the total force acting on the object is zero. This is because another force is acting in the opposite direction to gravity, and that is buoyancy. Buoyancy is a principle first discovered by the ancient Greek scientist Archimedes, and it occurs as a reaction to an object submerged in water pushing the water away. Its magnitude is equal to the weight of the water that the object pushes away, and the amount of water that the object pushes away is equal to the volume of the object in the water. In other words, an object floating on water pushes out water equal to its weight, and the object is in equilibrium with gravity and buoyancy.
An object sinking into water sinks because its weight is heavier than the weight of water equal to its volume. Therefore, whether an object floats or sinks in water depends on whether the mass per unit volume of the object, i.e. the density, is less or greater than the density of water. Submarines use this property to adjust their density in water and move.
So how can submarines adjust their density in water? They can adjust the density of submarines using buoyancy tanks. The buoyancy tank is a submarine structure consisting of a large hollow space that can be filled with air or water. When the submarine goes underwater, the buoyancy tank is filled with seawater to increase its density. When the submarine comes up to the surface, compressed air is injected into the buoyancy tank and the external valve is opened. When this is done, the seawater in the buoyancy tank is discharged to the outside and the inside of the buoyancy tank is filled with air, reducing the overall mass of the submarine. However, since the volume occupied by the submarine in the water remains the same, the submarine’s density also decreases. In this way, the average density of the submarine becomes less than the density of seawater, and the submarine can rise to the surface.
The buoyancy tank also plays a role in keeping the weight and buoyancy of the submarine equal so that the submarine can move at a certain depth underwater. At this time, the density of the submarine matches the density of seawater, and the buoyancy at this time is called neutral buoyancy. In the neutral buoyancy state, the submarine can maintain its depth and save fuel, making it efficient even for long-term diving operations.
The principle of such a submarine is the same as that of a fish’s swim bladder. Fish control their depth in the water using an organ called a swim bladder that can contain air. Therefore, a submarine ultimately controls its depth in the water by controlling gravity and buoyancy using the same principle as fish.
These features of submarines play an important role not only in military but also in scientific exploration. Ocean researchers are using submarines to explore the deep-sea environment, investigate seabed resources, and contribute to the protection of marine ecosystems. This is helping humanity to gain a deeper understanding of the Earth and the oceans.
