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Horrible news. Speaking of the physics involved, I was thinking: if it's just free fall, caused by gravity and no air sustaining the wings, this should not hap

Horrible news. Speaking of the physics involved, I was thinking: if it's just free fall, caused by gravity and no air sustaining the wings, this should not happen, right? Some random Quora answer says that it's because during turbulence there is actually air pressing wings down and accelerating them down faster than gravity, and that's why you hit the ceiling. Intuitively that makes sense but, can anyone confirm? Edit: because if it was just free-falling you should be in a micro-gravity environment

maxlamb 2y ago
The downdraft could actually make the plane accelerate downwards faster than free fall (even just for a second or so), hence everything unattached hitting the ceiling
kayodelycaon 2y ago
Air moves and the plane will move with it, subject to inertia. Think of the air like water. (Air has fluid dynamics.)If the water suddenly drops away from a boat, the boat isn’t going to magically hover above the water.
- darkwater 2y ago
  Obviously, but then the boat and all the objects within it would be experiencing the same gravity acceleration, immediately, at the same time.
  - deleted 2y ago
    [deleted]
  - xenadu02 2y ago
    > Obviously, but then the boat and all the objects within it would be experiencing the same gravity acceleration, immediately, at the same time. That is not correct. The airplane experiences this uniformly because the wings transmit the forces to the fuselage. But the contents of the aircraft follow Sir Issac Newton and want to continue their previous motion. If the aircraft experiences high enough negative G then anything not strapped down will appear to rise relative to the fuselage. To put it another way: you need a physical connection (eg seatbelt or cargo strap) to transmit the force in such an event, just as the fuselage needs a connection to the wings to transmit the force.
    - istjohn 2y ago
      OP was commenting on the analogy of a boat that has the water underneath it suddenly drop away.
    - darkwater 2y ago
      Still not convinced. The plane is both carrying you tangentially to the Earth surface (to simplify) and sustaining you against gravity. If a turbulence just makes disappear the sustain against gravity, the wings, the fuselage and everything inside will start free-falling at the same time, effectively being a reduced gravity system. This is what happens in the ISS and there is actually a NASA aircraft (Vomit Comet [1]) that does that on purpose. OTOH if the aircraft suddenly goes down faster than 1G, let's say 2G, and you are not tied to anything, you will experience a 1G acceleration towards the roof, because you are "just" falling at 1G. [1] https://en.wikipedia.org/wiki/Reduced-gravity_aircraft https://en.wikipedia.org/wiki/Reduced-gravity_aircraft
      - xenadu02 2y ago
        We covered this in the other thread but to give a simple summary: It is not purely a reduction in lift causing the aircraft to begin free falling. Different air masses can move in different directions, including downwards or in a circular motion. When the velocity of the air is high enough it can easily push the airplane down faster than free-fall otherwise would.
Faaak 2y ago
Same question here. I suppose that it also hurts (maybe even more?) on the way down because once the wings gain lift, you experience g + lift + your momentum going down ?
nick238 2y ago
You're assuming things are inelastic and won't 'bounce'. Pretend you're walking down the aisle: One second of higher-g: you compensate and your legs push harder against the ground. One second of weightlessness: the extra force you were pushing against launches you up, you lose footing and tumble. One second of higher-g: your flailing body is thrown against the ground from the average height of a few feet times the increased gravity. Ow.
ajross 2y ago
Free-fall, or really slightly negative G's, will lift you up out of your seat more or less gently. It won't hurt you. But when the aircraft regains lift, which can happen rapidly in turbulent conditions, you will accelerate downward relative to the cabin. And the plane is design-tested to something like 5G. It can hurt you very badly.
- darkwater 2y ago
  But then you should hurt your butt, not your head as described in the article, no? I still think that if you get your head against the oxygen masks it's because the plane accelerated a lot downwards.
  - xenadu02 2y ago
    When the airplane experiences high negative G you get propelled upwards at 9.8m/s/s times the negative G. A -1G force cancels the constant +1G force gravity exerts resulting in free-fall or floating. If the negative G force is higher than 1G you are now accelerating upwards relative to the fuselage. A -2.5G event "pulls" you upward 1.5x harder than falling and you absolutely can die from falling down due to head injury - it happens all the time. In reality it doesn't pull, your inertia simply wants to keep you moving as you were so the top of the fuselage "falls" faster than gravity until it connects with your body and is able to transmit that force to counter your inertia. A better way to transmit that force is a seat belt. This is exactly the same situation as a car hitting a wall and why you need a seat belt in that scenario too. You and the car are moving forward. The car decelerates. When it does so faster than the friction of you in the seat your inertia carries your body forward. The faster the car stops the more energy you have to impact the windshield/steering wheel/etc. The seat belt functions to transmit the force between your body and the car.
    - kQq9oHeAz6wLLS 2y ago
      In other words, the people didn't "fly up" and hit their heads, the plane fell on top of them. Granted they were technically falling, too, but at a slower rate because the force that pushed the plane down - turbulence - acted directly on the plane, but the plane shielded the passengers from the direct effect of the turbulence. Thus the air did not push them down at the same rate that it pushed the plane down onto them.

maxlamb 2y ago

The downdraft could actually make the plane accelerate downwards faster than free fall (even just for a second or so), hence everything unattached hitting the ceiling

kayodelycaon 2y ago

Air moves and the plane will move with it, subject to inertia. Think of the air like water. (Air has fluid dynamics.)If the water suddenly drops away from a boat, the boat isn’t going to magically hover above the water.

darkwater 2y ago
Obviously, but then the boat and all the objects within it would be experiencing the same gravity acceleration, immediately, at the same time.
- deleted 2y ago
  [deleted]
- xenadu02 2y ago
  > Obviously, but then the boat and all the objects within it would be experiencing the same gravity acceleration, immediately, at the same time. That is not correct. The airplane experiences this uniformly because the wings transmit the forces to the fuselage. But the contents of the aircraft follow Sir Issac Newton and want to continue their previous motion. If the aircraft experiences high enough negative G then anything not strapped down will appear to rise relative to the fuselage. To put it another way: you need a physical connection (eg seatbelt or cargo strap) to transmit the force in such an event, just as the fuselage needs a connection to the wings to transmit the force.
  - istjohn 2y ago
    OP was commenting on the analogy of a boat that has the water underneath it suddenly drop away.
  - darkwater 2y ago
    Still not convinced. The plane is both carrying you tangentially to the Earth surface (to simplify) and sustaining you against gravity. If a turbulence just makes disappear the sustain against gravity, the wings, the fuselage and everything inside will start free-falling at the same time, effectively being a reduced gravity system. This is what happens in the ISS and there is actually a NASA aircraft (Vomit Comet [1]) that does that on purpose. OTOH if the aircraft suddenly goes down faster than 1G, let's say 2G, and you are not tied to anything, you will experience a 1G acceleration towards the roof, because you are "just" falling at 1G. [1] https://en.wikipedia.org/wiki/Reduced-gravity_aircraft https://en.wikipedia.org/wiki/Reduced-gravity_aircraft
    - xenadu02 2y ago
      We covered this in the other thread but to give a simple summary: It is not purely a reduction in lift causing the aircraft to begin free falling. Different air masses can move in different directions, including downwards or in a circular motion. When the velocity of the air is high enough it can easily push the airplane down faster than free-fall otherwise would.

Faaak 2y ago

Same question here. I suppose that it also hurts (maybe even more?) on the way down because once the wings gain lift, you experience g + lift + your momentum going down ?

nick238 2y ago

You're assuming things are inelastic and won't 'bounce'. Pretend you're walking down the aisle: One second of higher-g: you compensate and your legs push harder against the ground. One second of weightlessness: the extra force you were pushing against launches you up, you lose footing and tumble. One second of higher-g: your flailing body is thrown against the ground from the average height of a few feet times the increased gravity. Ow.

ajross 2y ago

Free-fall, or really slightly negative G's, will lift you up out of your seat more or less gently. It won't hurt you. But when the aircraft regains lift, which can happen rapidly in turbulent conditions, you will accelerate downward relative to the cabin. And the plane is design-tested to something like 5G. It can hurt you very badly.

darkwater 2y ago
But then you should hurt your butt, not your head as described in the article, no? I still think that if you get your head against the oxygen masks it's because the plane accelerated a lot downwards.
- xenadu02 2y ago
  When the airplane experiences high negative G you get propelled upwards at 9.8m/s/s times the negative G. A -1G force cancels the constant +1G force gravity exerts resulting in free-fall or floating. If the negative G force is higher than 1G you are now accelerating upwards relative to the fuselage. A -2.5G event "pulls" you upward 1.5x harder than falling and you absolutely can die from falling down due to head injury - it happens all the time. In reality it doesn't pull, your inertia simply wants to keep you moving as you were so the top of the fuselage "falls" faster than gravity until it connects with your body and is able to transmit that force to counter your inertia. A better way to transmit that force is a seat belt. This is exactly the same situation as a car hitting a wall and why you need a seat belt in that scenario too. You and the car are moving forward. The car decelerates. When it does so faster than the friction of you in the seat your inertia carries your body forward. The faster the car stops the more energy you have to impact the windshield/steering wheel/etc. The seat belt functions to transmit the force between your body and the car.
  - kQq9oHeAz6wLLS 2y ago
    In other words, the people didn't "fly up" and hit their heads, the plane fell on top of them. Granted they were technically falling, too, but at a slower rate because the force that pushed the plane down - turbulence - acted directly on the plane, but the plane shielded the passengers from the direct effect of the turbulence. Thus the air did not push them down at the same rate that it pushed the plane down onto them.