Could any of these possibilities really bring a person into the sky?

To be clear.

An adult weighs at least a hundred pounds, and can weigh more than two hundred pounds.

Counting the weight of the carrier, the most conservative estimate is over 200 pounds, right?

How could such a heavy object possibly lift off into the air?

But Xu Yun had already proven his abilities before; his words shouldn't be easily dismissed...

Then Old Su paused for a moment, considering the importance of the matter of 'auspicious', and decided to learn more about the inside story:

"Xiaowang, is there a principle that can explain this thing you call an airplane?"

"A principle...?"

Xu Yun thought for a moment, then pulled out two sheets of paper from his pocket—he had mentioned earlier at the Fan Building that he always carried paper and a pen.

Then he held one end of the paper in each hand, letting the paper hang down naturally.

He asked Old Su and Xiaozhao:

"Your Highness, Sir, do you remember the experiment we did in class back then?"

Old Su and Xiaozhao exchanged glances, their expressions thoughtful, and after a moment replied:

"Of course we remember, it was called the Bernoulli principle, wasn't it?"

Xu Yun nodded:

"That's right."

Then he paused and continued:

"Your Highness, Sir, since you both remember the Bernoulli principle, could there be a possibility?"

"For example, if we replaced the paper with a fixed object, using techniques to create a significant speed difference between the airflows above and below....."

"In this way, couldn't we make the object float up like a piece of paper?"

Students with good memories should still remember.

Xu Yun had demonstrated the paper blowing experiment for Xiaoli when they first met.

Later, in class, Xiaoli specifically asked Xu Yun about it, and to explain it easily, Xu Yun casually demonstrated another high school experiment:

Hold one end of the paper in each hand, let it hang down naturally, and blow between the two papers.

As you keep blowing, you'll find...

The two papers actually stick together.

In the high school textbook, these two experiments are both attributed to the Bernoulli principle:

Look, the flow speed is high and the pressure is low above, so the paper floats up.

But in reality....

This is wrong.

The paper blowing demonstration Xu Yun did for Xiaoli had little to do with the Bernoulli principle.

Actually, this is a widespread misunderstanding of the Bernoulli equation.

Considering that some fools... cough, cough, the information barriers of lay readers, to put it simply:

The Bernoulli equation holds along the same streamline, not between different streamlines.

The direction the paper shifts depends not on which side the airflow is, but on the angle between the airflow direction and the paper, related to viscosity.

Initially,

The paper hangs vertically down.

Blowing air over the top of the paper will cause the right side air to be taken away due to viscosity.

As a result, a low-pressure area forms.

The presence of this low-pressure area causes the paper to float upward to the right.

As the paper floats, the streamline bends downward.

Eventually, it makes the streamline cling to the paper.

At this point, the airflow no longer travels straight ahead, but follows a downward curve, which is a vortex field.

Thus, the downward bent streamline creates a centripetal force, which lifts the paper up.

This effect is truly called the Coanda effect, not the Bernoulli principle.

Very simple and easy to understand, right?

Yet in high school classrooms,

when discussing airplane principles, teachers not only fail to explain the Coanda effect (a considerable number of them might not even realize they are wrong themselves), they often extend the paper example further.

That is, they replace the paper with a wing:

For a wing, the upper surface is more convex, so airflow speeds up over it.

This creates a pressure difference, which is the source of lift.

With this explanation plus the paper experiment, most people suddenly see the principle behind airplanes flying:

Oh, so airplane principles are this simple...

And so, a situation of repeated mistakes arises—the principle of airplanes is the Bernoulli principle.

Actually, if anyone cared to think about it, they could easily come up with two counter-questions:

First, why can stunt planes fly upside down?

Second, why does a kite, essentially a big flatboard, fly without power?

Of course,

one can think about these questions, but it's not advisable to challenge teachers with them in class.

Otherwise, you might end up with a reward of standing punishment and copying homework, and the unlucky ones may even get a scolding from the class teacher.

All in all,

up to now, including the Bernoulli principle, Newton's third law, the Venturi effect, the Kutta-Joukowski theorem, and many other modified laws, it's actually hard to perfectly explain the issue of lift.

Why airplanes can fly remains an unsolved mystery.

People say the Nobel Prize is distant, but actually, many common phenomena in life, if successfully explained, would seem to place the Nobel Prize within easy reach.

But on the other hand,

as mentioned long ago:

The Song Dynasty is not the 21st century, and for the basic understanding of the current era, some concepts don't necessarily need to be perfectly accurate.

A more general explanation is easier for people to understand.

Therefore, when Xu Yun was explaining the reason back then, he directly applied the Bernoulli principle to the paper.

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