I have this doubt :

Why is pressure inside an aeroplane so less than the ground atmospheric pressure? I have heard that some kids even have there ear popped off. Although the atmospheric air pressure is low, as the no: of mols of air inside the volume of the plane is constant (The chamber is sealed), and the temperature is maintained, pressure inside the plane is supposed to also remain constant. But the pressure really decreases, as even if you have tried keeping a plastic bottle airtight while you are onboard, when you land on the airport, the bottle would be crushed. This is because the pressure inside the bottle is same, but outside had increased. How can this happen, when the plane is also airtight? How can the pressure inside an aeroplane drop when you are at an altitude, and rise when you are back on the terrain.

Please explain my mistake. I have assumed ideal conditions.

It's great that you're curious about the pressure differences experienced in an airplane compared to ground level! This topic involves some fascinating principles of physics and atmospheric science. Let's break it down step by step to clarify your understanding.

The Basics of Atmospheric Pressure

Atmospheric pressure is the weight of the air above us pressing down. At sea level, this pressure is about 101.3 kPa (kilopascals). As you ascend in altitude, such as when you're flying in an airplane, the amount of air above you decreases, leading to lower atmospheric pressure. This is why, at cruising altitudes (typically around 30,000 to 40,000 feet), the pressure outside the airplane is significantly lower than at ground level.

Understanding Airplane Cabin Pressure

Airplanes are designed to be pressurized environments. While the cabin is sealed, it doesn't mean that the pressure inside remains constant at all times. Instead, the cabin pressure is maintained at a level that is comfortable for passengers, usually equivalent to the pressure found at about 6,000 to 8,000 feet above sea level, which is significantly lower than ground level but higher than the outside pressure at cruising altitude.

Why Does Pressure Change During Ascent and Descent?

As the airplane climbs, the external atmospheric pressure decreases rapidly. The cabin pressure is controlled by the aircraft's pressurization system, which adjusts the amount of air pumped into the cabin to maintain a safe and comfortable environment. However, this system cannot completely equalize the pressure with the ground level pressure. Instead, it keeps the cabin pressure at a level that is manageable for passengers.

Example of Pressure Changes

• During ascent, the external pressure drops, but the cabin pressure is maintained at a higher level.
• When the airplane descends, the external pressure increases, and the cabin pressure is adjusted to match the rising external pressure.

The Plastic Bottle Analogy

Your observation about the plastic bottle is a great analogy. When you take a sealed bottle onto the plane, the air inside is at a certain pressure. As the airplane climbs, the external pressure drops, but the pressure inside the bottle remains the same. When you land, the external pressure increases rapidly, and since the bottle is sealed, the higher outside pressure can crush it. This illustrates how pressure differences can affect sealed containers.

Ear Popping Explained

The phenomenon of ears popping during ascent and descent is related to the pressure changes affecting the air in your Eustachian tubes, which connect your middle ear to the back of your throat. When the airplane ascends, the pressure in the cabin decreases, and if the Eustachian tubes do not equalize the pressure quickly enough, you may feel discomfort or a popping sensation. The same happens during descent when the external pressure increases.

Key Takeaways

• The pressure inside an airplane is lower than at ground level but is maintained at a comfortable level.
• Pressure changes occur due to the difference between cabin pressure and external atmospheric pressure.
• Sealed containers, like plastic bottles, can experience crushing due to rapid changes in external pressure.

In summary, while the airplane cabin is pressurized, it does not match ground-level pressure, and the changes in altitude create significant pressure differences that affect both the cabin environment and any sealed objects inside. Understanding these principles helps clarify why you experience these sensations during flights!