When we travel by airplane, the pressure changes. What does that mean exactly? Why does it make my ears hurt?
Equally, deep sea diving and submersibles. Ive read that the glass has to be massively reinforced to stand the pressure. Is the change in pressure the same type for air and sea? I.e does pressure increase for both?
Edit; Everyone did great! I understand now! The answer is “Water be heavy” and “Air be heavy. Less air above you when you fly so less pressure”
In: 13
Pressure is the way fluids confer forces applied to them everywhere they go.
Air (or any gas) is like a spring, if force is applied to one end, it pushes on the other; but if it is pushed on from both sides, it compresses. Without Earth pulling the air down, it would un-spring away into space quite tremendously.
That’s why you can have pressure containers and vacuum chambers: you can stretch or compress that air spring. Releasing it will make air flow in or out. And if the spring is too strong, the container may burst violently.
Meanwhile, water (or any liquid) is more like a rigid metal rod, it almost won’t compress, definitely not in a way you can notice. Pushing against it will do nothing unless something somewhere else gives in.
Thus water in a container is just there (or not). It is not a loaded spring. Yet it will conduct forces through it.
In your typical life, the air and water pressures result from their weight. Hold a large bucket of water up, it takes quite a bit of force to do so. Now imagine that above you, right now, there are dozens of kilometers of air. While air is quite light, it still weighs a bit, roughly a thousandth of the same volume of water. In other words, there are effectively a few meters (~10 to be exact) of water pressing down. That’s a lot more than you can likely lift. Going with the analogue, there is a high stack of springs, and their weight compresses the bottom ones quite a bit. Hence why the atmospheric pressure goes down when you go up.
To put it into numbers, that’s about 10 tons (~2 elephants) per square meter. So several elephants are continuously stepping on you. Luckily, the matter in your body withstands it easily. You can actually have an elephant step onto a thin porcelain plate without breaking as long as the plate is well-supported from below. Solid and liquid things are almost indestructible as long as all forces are fully countered in every direction.
Hence why you usually do not feel the air pressure, it is (almost) the exact same from all directions: you essentially get squished together from everywhere, but you are not a soft foam ball, but a blob of water and bones. Maybe you get smaller by a millionth of your size compared to being in the vacuum of space; you simply won’t notice even if you try to compare (not recommended!).
Your ears hurt, because there is just the slightest bit of difference between the in- and outside. When the airplane rises (or sinks again), the outside pressure changes as we have seen with the springs. But if the various caverns in your head are clogged, usually by mucus, it takes quite some time for the inner pressure to follow suit. Therefore there is now a difference in pressure, maybe a few percent at worst. Still enough to hurt quite a bit on something as fine and thin as an eardrum.
Underwater, the pressure is much higher. As we saw, ~10 meters of water is about all the atmosphere above us. Thus at 10 kilometers depth, we have a thousand times(!) our typical pressure. In other words, a ton per square centimeter, or an elephant per finger.
If you want to have not just one but an entire vertically stacked and huge horde of elephants to be held up by a glass pane, you need one very thick boy of one. Hence why we usually only do small windows surrounded by massive steel on submersibles.
First, let’s talk about bricks. One brick weighs so much. A stack of two weighs twice as much. a stack of three weighs 3 times as much. etc, etc. Each brick you add increases the stack height and weight by one brick.
Now, let’s talk about pillows. One pillow weighs so much. A stack of two weighs twice as much. A stack of three weighs 3 times as much. etc, etc. As you add more pillows to the stack, the weight increases by one pillow, but the lower pillows in the stack are squished by the weight so the height does not increase by one pillow. Also, the lower pillows are now more dense, as their fluffiness has reduced by this squishing.
The gas molecules and atoms act kind of like pillows. They aren’t in an ordered stack, but in a moving heap around the planet. The lower they are in the heap, the more dense they are due to being squished under the heap. Likewise, the higher they are in the heap, the less dense they are due to there being less atoms and molecules above them to squish them.
The thing that gets your ears when changing altitude is the pocket of trapped air inside your inner ear. This air causes no discomfort when the pressure inside your ear is the same as the pressure outside of it.
As you move to an a higher altitude, there’s less air pressure on the outside of your ear drum. The air trapped in your ear drum expands as it matches match the pressure around you. If it cannot find a way out, it expands your inner ear kind of like a balloon but a little less dramatic. When you yawn (or whatever), the inner ear hole (Eustachian tube) is opened and excess air is able to escape.
Likewise, when you go to a lower altitude the air pressure increases, and your ear drum is squished from the outside because there is not enough air inside. Yawning (or whatever) allows more air to go into the inner ear hole, equalizing the pressure.
#ELI5
Put on your pants, and then **put a belt on**.
Now make the belt **REAL TIGHT**.
It’s kind of uncomfortable, right? I mean, your guts are compressed. You’re not accustomed to that level of tightness. Your gut isn’t accustomed to that kind of tightness.
Now loosen the belt a little, and notice that your gut kind of expands. The loosened belt *allows* your gut to expand.
The air is really kind of like a belt! You don’t notice it walking around, because “the belt” is not too tight, not too loose. It feels “just right” because THIS is the level of tightness you’re accustomed to.
The “tightness of the belt” is the same as the “pressure of the air”.
When you go way high up in the sky, there’s less and less air pressure. Why? I’ll let someone else explain that. Just accept that there is less air pressure … the “belt” is becoming looser!
So your body is accustomed to a “tighter belt” at ground level, and it’s not accustomed to a “looser belt” at high altitudes.
When you loosened your belt around your waist, your gut expanded. When you “loosen the belt” of air pressure by going high up in the sky … other parts of your body “expand”.
It turns out that your eardrums, which are tiny membranes, are accustomed to the air pressure at ground level. That’s where they’re most comfortable.
But reduce air pressure, by going up high … and now your eardrums “expand” just like your gut would when you loosen your belt.
And because you’re not accustomed to this, it may hurt a little bit.
THAT is why you hear of “pressurizing the cabin” in an airplane. The air up there is at lower pressure than you’re used to. But the plane is a sealed container, and they increase the air pressure inside the plane with fans and pumps and such. It’s like putting you inside a massive bicycle tire and pumping up the tire with a pump.
Why do they do this on airplanes? Because it increases the air pressure to a level you’re comfortable at.
Sometimes it’s not immediate … and the air pressure you feel isn’t right at that sweet-spot you’re comfortable at. And so again, you feel a pressure difference, and your ears feel it too.
DEEP SEA DIVING is the same principle, but not air pressure. Instead, we’re talking about water pressure.
We discussed how air pressure is less as you go up. So air pressure is more as you go down. WATER pressure is the same way. Water pressure is less at the surface, and water pressure is HIGHER as you go down.
And so, yes, a submarine that is able to withstand the water pressure at 5 meters of depth, must be reinforced to withstand the water pressure at 500 meters of depth.
Imagine tightening your belt around your waist so much, that you actually hurt yourself. Maybe your colon ruptures, because of the great pressure from the belt.
If you send a submarine down so far, to the point where it can’t withstand the pressure anymore, then the “belt” of water will crush the submarine (because of higher pressure), just like your belt around your waist will crush your internal organs.
**PEOPLE PEOPLE PEOPLE** …. This is ELI5. This is not 100% accurate, by far, but it paints a good enough picture to get the basics across.
First, let’s talk about bricks. One brick weighs so much. A stack of two weighs twice as much. a stack of three weighs 3 times as much. etc, etc. Each brick you add increases the stack height and weight by one brick.
Now, let’s talk about pillows. One pillow weighs so much. A stack of two weighs twice as much. A stack of three weighs 3 times as much. etc, etc. As you add more pillows to the stack, the weight increases by one pillow, but the lower pillows in the stack are squished by the weight so the height does not increase by one pillow. Also, the lower pillows are now more dense, as their fluffiness has reduced by this squishing.
The gas molecules and atoms act kind of like pillows. They aren’t in an ordered stack, but in a moving heap around the planet. The lower they are in the heap, the more dense they are due to being squished under the heap. Likewise, the higher they are in the heap, the less dense they are due to there being less atoms and molecules above them to squish them.
The thing that gets your ears when changing altitude is the pocket of trapped air inside your inner ear. This air causes no discomfort when the pressure inside your ear is the same as the pressure outside of it.
As you move to an a higher altitude, there’s less air pressure on the outside of your ear drum. The air trapped in your ear drum expands as it matches match the pressure around you. If it cannot find a way out, it expands your inner ear kind of like a balloon but a little less dramatic. When you yawn (or whatever), the inner ear hole (Eustachian tube) is opened and excess air is able to escape.
Likewise, when you go to a lower altitude the air pressure increases, and your ear drum is squished from the outside because there is not enough air inside. Yawning (or whatever) allows more air to go into the inner ear hole, equalizing the pressure.
To bring this specifically to aircraft. The air conditioning system control the cabin temperatures and cabin pressure. On the ground normal pressure would be 14.7psi (1atm). As the aircraft climbs and the outside air pressure drops, the air conditioning systems works harder to maintain the the pressure inside the cabin at a “comfortable” level. Usually this is around 8-9PSI depending on the aircraft which would be equivalent to being at 8’000ft even though you might be flying at 30’000ft or higher.
To bring this specifically to aircraft. The air conditioning system control the cabin temperatures and cabin pressure. On the ground normal pressure would be 14.7psi (1atm). As the aircraft climbs and the outside air pressure drops, the air conditioning systems works harder to maintain the the pressure inside the cabin at a “comfortable” level. Usually this is around 8-9PSI depending on the aircraft which would be equivalent to being at 8’000ft even though you might be flying at 30’000ft or higher.
To bring this specifically to aircraft. The air conditioning system control the cabin temperatures and cabin pressure. On the ground normal pressure would be 14.7psi (1atm). As the aircraft climbs and the outside air pressure drops, the air conditioning systems works harder to maintain the the pressure inside the cabin at a “comfortable” level. Usually this is around 8-9PSI depending on the aircraft which would be equivalent to being at 8’000ft even though you might be flying at 30’000ft or higher.
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