The misery of school

[SebastianL]

[Remundo]

For those who want a theoretical demo, confirmed by practice...

reasoningalamasse.png (31.15 KiB) Consulted 779 times

[SebastianL]

[the air as a whole is not accelerated]

Good luck demonstrating the lift of the wing

[Exnihiloest]

For those who want a theoretical demo, confirmed by practice...

Unbelievable ! That's right !

In addition there is a whole bunch of ad absurdum reasoning which makes it possible to understand that an airplane's weight which would not refer to the ground would mean that the weight of the air should not refer to the ground either, not to mention the analogy already made with water and a floating object.

[Remundo]

[the air as a whole is not accelerated]

Good luck demonstrating the lift of the wing

there is nothing contradictory there.

Air is a system of infinitesimal material masses. They can have accelerations.

But a fixed center of gravity.

[FALCON_12]

This is the whole failure of the school. Not only do we not see intuitively what is happening, but the simple and unstoppable theoretical reasoning which consists in saying that the mass and therefore the weight of the box+fly assembly has not necessarily varied since the fly is still in the box n was not seen either

False, the fly floats in the air and its weight is no longer added to the box.

Do you realize that you are saying that if, to show it well, the fly is now a 1kg drone and the box weighs 1kg too, and also someone is carrying this box in their hand, after the drone has taken off the carrier will only have 1 kg to carry?

And what are you saying, you who have studied, that we could cancel certain weights by this anti-gravitational technique?

Don't you see that all the grains of matter caught in the gravitational field of the planet pile up on top of each other and that the only way to stay in the air is to lean directly or indirectly on matter who is below?

Everything is drawn down (the center of the planet) and everything is piling up! whether it's gas or earth, the density doesn't matter! each elementary cube of matter can only hold in the air by leaning directly (direct chain towards the center) or indirectly (chain in the form of a gallows, as in the case of the airplane wing with the depression on the upper surface, the lift and the overpressure zone distributed on the ground).

In other words imagine that you yourself are a gravitational center of attraction. For the moment you are in front of me and no mass has yet come to stick to you. I place in your field of attraction a first molecule, it is an iron molecule. She comes to stick to you. During the next hour I continue with kilos of other molecules. Earth, water, gas, metals etc. They all come to stick to you and you feel increasing pressure. Each new kilogram of material that sticks to you crushes you a little more.

Now I stop and we wait a bit. Matter organizes itself in less and less dense layers around you. Like in a cocktail. The densest near you. You have become a small magma planet at 37°C.

You feel crushed and this crushing is also due to a 10 kg plane on your ground.

Now the plane takes off. Do you feel less overwhelmed? do you no longer attract him? is there less matter in your gravitational field? Did the fact that the plane changed its altitude in your field of attraction where everything pile up towards you change anything for you?

Do you see/feel all of this? do you imagine it? do you understand ? do you see?


Could an airplane fly on a planet without "ground"? Yes ! because there would always be something to lean on/pile up on, that is to say more and more dense matter as one approaches the center. Because there is always "a ground", whether the density makes a sudden jump (passage from air to earth on our planet) or increases more linearly on a gaseous planet.

[sicetaitsimple]

Do you realize that you are saying that if, to show it well, the fly is now a 1kg drone and the box weighs 1kg too, and also someone is carrying this box in their hand, after the drone has taken off the carrier will only have 1 kg to carry?

Um, yes, but you may not have noticed that the drone is equipped with motors that do the job...
Just as an airplane, if its engines produce a horizontal thrust which makes it move forward, indirectly produce, because of the geometry of the wing, a vertical "suction" which is called lift? Great no, a horizontal force that turns into a vertical force!!!
Science is advancing...

[Exnihiloest]

...
Nah, that's what I wrote. There is indeed a mass but there is no (or very little) weight as long as the plane is flying. And "put a floating object on the water", I also answered:JUntil touchdown, the apparent weight of the plane is almost zero, at least low enough for the descent to be done gently and in a controlled manner. As soon as he touches, it goes to mg.. As soon as there is contact with a solid, or even a liquid, the basin and the scales actually work.

The question was asked on Quora. All the answers confirm that the weight of the plane is indeed transferred to the ground, with supporting explanations. You and Izen have it all wrong.

"Is the weight of the aircraft flying in the sky transferred to the ground?"
Conclusion 1st answer:
"So the weight of the plane is put into the air around, below, and behind the plane. The air is doing all the work and supporting the plane. And yes, indirectly, the ground is also supporting the air, so the weight does eventually get transferred to the ground."

2nd conclusion, following a comparison with the hydraulics as I did:
"The lake bed earlier was supporting the weight of only the water, but now it will have the additional weight of the barge. It's exactly the same with airplanes and the atmosphere."

3rd and best answer in my opinion (Sherer). Translation :
"Take a cubic mile of atmosphere and measure its weight. It's hard to do, but it's just a thought experiment. Now fly a jumbo jet through that cubic mile of atmosphere and measure again. Is it heavier? Even more spectacularly, fly a hundred jumbo jets in the same cubic kilometer of atmosphere. It's a little denser and extremely turbulent, but how is the mass of that cube of air compared to the mass without planes in. It is the initial air mass, minus the mass of air replaced by the volumes of the jumbo jets, plus the mass of certain shock waves due to the expansion of the air masses, plus, of course, the masses of the jumbo jets. As the jumbo jets are heavier than the air they replace, the total mass of the jumbo cubic mile is really heavy and it will compress the air below until on the surface of the earth for a while. And during this instant, the total weight of the plane flying in the sky is transferred to the ground. And this is true for every cubic kilometer of our globe's atmosphere, and for every heavier-than-air flying object they replace, even mosquitoes.."

4th equally convincing answer (Grimshau):
"Air is pulled down by gravity, just like anything else with mass. It's what keeps the atmosphere on the planet, no different from keeping water in the oceans.
In fact, that's why we have air pressure - the ground stops the air falling and so the air is compressed against the ground by the weight of the air above. Therefore, we can calculate the force of the atmosphere on the ground from the atmospheric pressure [...], the atmospheric weight on the ground is [...] approximately the weight of 10 tons per square meter.
So the atmosphere that supports an airplane is just a slightly heavier atmosphere. A Jumbo jet has a mass of the order of 500 tons, and of course the atmosphere below distributes the resulting additional weight over a large ground area., depending on the height of the aircraft. As the ground already supports about 10 tons per square meter, the weight of the aircraft when spread over a large area becomes a negligible addition."

Morrow's answer is also enlightening, see his diagram with the integral of the pressure around the plane which indicates an overpressure downwards where the plane passes, therefore an increase in atmospheric pressure, which will be found, spread out, on the ground...

All the other answers confirm that the weight of the plane is well transferred to the ground. We have to stop the bad faith.

[Remundo]

Could an airplane fly on a planet without "ground"? Yes ! because there would always be something to lean on/pile up on, that is to say more and more dense matter as one approaches the center. Because there is always "a ground", whether the density makes a sudden jump (passage from air to earth on our planet) or increases more linearly on a gaseous planet.

I would go even further in the reasoning.

Even if the planet is 100% gaseous, the weight of the plane is found up to the center of the planet by pressure.

the fact that this plane changes altitude will vary a little bit the pressure of the center, and of all the intermediate layers.

In practice there is often a dense, liquid core (or solid, we don't really know, dense we're sure) in the planets On Earth, the ground is a thin crust, but all the gravitational forces are transmitted to the center under the form of pressure.

there are funny problems of statics of fluids where we consider 100% liquid or gaseous planets, we apply grad(P) = ro xg with a formula ro=f(P) as hypothesis.

[sicetaitsimple]

All the other answers confirm that the weight of the plane is well transferred to the ground. We have to stop the bad faith.

OK, OK, you're right, of course the atmosphere below distributes the resulting additional weight over a large floor area
But since by design an airplane in flight at a constant altitude has almost zero weight (otherwise it would climb or descend permanently), this is not dramatic....