Why Can Submarines Not Dive Deeper Than Airplanes Can Fly High?

The confusion surrounding the depth that submarines can dive and the height that airplanes can fly arises from a misunderstanding of the basic principles of atmospheric and hydrostatic pressure. This article aims to clarify these concepts and explain why submarines are limited in their depth, whereas airplanes are limited in their altitude.

The Physics Behind Airplane Pressurization

Airplanes are pressurized to ensure that the air inside the cabin remains at a comfortable sea-level pressure. This is crucial for the comfort and health of passengers and crew members. The air pressure inside the airplane is higher than the external atmospheric pressure, which allows for the survival and well-being of the crew and passengers. At higher altitudes, the air pressure decreases, and pressurization is necessary to maintain the same air pressure that is experienced at sea level.

Submarines and Hydrostatic Pressure

Submarines, on the other hand, operate at a standard atmospheric pressure, or 1 atmosphere (1 atm), to ensure the comfort of the crew. This is significantly lower than the pressure exerted by seawater at depth. Submarines are designed to withstand the external pressure of the water, which increases with depth. As a result, the air pressure inside a submarine remains relatively stable, similar to the pressure at the surface of the water. For instance, at the deepest point in the ocean, the Mariana Trench, the water pressure is approximately 1000 atmospheres, a formidable challenge for standard submarines.

Why Can't Submarines Go Deeper?

The primary limitation for submarines is the pressure exerted by the water as they dive deeper. As a submarine descends, the water pressure increases exponentially. For a standard submarine, this pressure would quickly become lethal for human life. If a submarine were to maintain the same internal pressure as the external water pressure, it could indeed dive to great depths. However, doing so would be extremely dangerous, as the pressure would kill the crew within a few hundred feet of descent.

Specialized deep-diving submarines do exist and can reach depths of several thousand feet. However, these are equipped with advanced technologies and materials to withstand the extreme pressures involved. In an emergency, submarines can be pressurized to match the external water pressure, but this can only be sustained for extremely short periods, typically a few hundred feet at most.

Comparison with Airplanes

Similar to how submarines are limited in depth by water pressure, airplanes are limited in altitude by atmospheric pressure. The typical cruising altitude for a commercial airline is around 36,000 feet. At this height, the external air pressure is about one-third of the pressure at sea level. Pressurization is essential for the survival and comfort of the passengers and crew. Military aircraft can fly at even higher altitudes, but they also require pressurization to ensure the safety of the aircrew.

The key difference lies in the medium: air and water behave differently under pressure. Airplanes can fly to higher altitudes because they simply do not encounter the same extreme pressure changes as submarines do in the ocean. While the external pressure increases with altitude, it does not increase as dramatically as it does with depth in the ocean.

Aerial and Aquatic Boundaries

The fundamental concepts of pressure in aquatic and atmospheric environments are quite distinct. The density of air and seawater are very different, affecting the way pressure changes with altitude and depth. Air is less dense and therefore more compressible, allowing airplanes to fly to much higher altitudes without the same dangers faced by submarines.

Understanding these principles is crucial for the safe operation of both submarines and airplanes. While a submarine can theoretically dive to any depth by matching the external water pressure, the practical limitations of survival and material strength dictate that it must remain within certain depth limits. Similarly, airplanes can fly to great heights by maintaining a constant pressure inside the cabin, but their altitude is ultimately limited by the thinning of the atmosphere.

In conclusion, the limitations on the depths that submarines can achieve and the altitude that airplanes can reach are governed by the unique properties of the environments in which they operate. Understanding these differences is essential for the safe and efficient operation of both naval and aviation technologies.