1The Secret of the Ballast Tanks
Submarines are like incredible underwater spaceships designed to explore the deep, dark corners of the ocean. To move up and down, they rely on a clever piece of engineering called ballast tanks. These are large compartments located between the inner and outer hulls of the ship. When a submarine is cruising on the surface, these tanks are filled with air, which makes the vessel light enough to float. However, when it is time to explore the depths, the crew opens "flood valves" to let heavy ocean water rush in. As the air is pushed out and replaced by water, the submarine becomes much heavier, allowing it to slide beneath the waves.
2Understanding Density and Buoyancy
The reason a submarine can sink or float on command comes down to a scientific concept called density. Density is a measure of how much "stuff" is packed into a space. Water is much denser than air. When the ballast tanks are full of air, the submarine's overall density is less than the water around it, so it stays buoyant and floats. By flooding the tanks with seawater, the submarine's total weight increases until its density is greater than the ocean water. This creates "negative buoyancy," which pulls the submarine down. Engineers have to calculate these weights perfectly to ensure the sub doesn't sink too fast!
3Rising Back to the Surface
Coming back up to the sunlight requires a process called "blowing the ballast." Submarines carry tanks of highly compressed air. To rise, the crew releases this high-pressure air into the ballast tanks, which forcefully blasts the water back out into the ocean through the valves at the bottom. As the water leaves, the submarine becomes lighter and its density drops. Like a giant underwater balloon, the vessel begins to float upward. Some modern military submarines can dive to depths of over 1,500 feet, which is deeper than the Empire State Building is tall!
