In class today, the teacher asked us, What is the principle of an airplane? Uninhabited? Who knows?

According to Bernoulli's principle, in a stream of water or air, if the velocity is small, the pressure is high, and if the velocity is high, the pressure is small. Because the upper and lower arcs of the wing of the aircraft are not symmetrical, the curvature of the upper wing surface is greater than the lower wing surface, so that when the air flows through the streamlines above the wings are dense and the flow velocity is large, the streamlines below are sparse and the flow velocity is small, and the pressure above the wing is small and the pressure below is strong by Bernoulli's equation, so that the pressure difference is generated, and when the total pressure difference reflected in the wing surface is greater than the weight of the aircraft, the aircraft can fly into the sky. So how do you get air to flow through the wings at high speed?

This requires the aircraft to have a large relative velocity to the air, so people invented the propeller and later the jet engine, both of which can make the aircraft produce forward motion, so the air and the aircraft have a relative motion, and the relative velocity is generated. Therefore, in the past, in order to take off on a shorter runway, the aircraft on the aircraft carrier usually adjusted the course of the aircraft carrier so that the aircraft took off against the wind, so that a larger wing air flow velocity could be obtained, and the take-off distance would be shortened. Of course, modern aircraft carriers are equipped with take-off "catapults", the role of which is also to obtain a large wing air flow velocity.

Katyn**, the Soviet Union killed 30,000 Polish officers and soldiers in World War II. Why do you history teachers ask such details? In the history of World War II, there was a ...... more powerful than this

It's very simple, just write down the reasons why you can't come back. If you don't review well, you don't pay attention to lectures in class, you don't pay attention to think about other things, etc., just admit your mistakes and write down how to improve them in the future.

I don't have an idea when you write like that.

Landlord, I'm the teacher. I would laugh at the student and go to class on and off, not taking it to heart.

Yes, the teacher will think you are rude.

Well, probably not.

It's not a big deal.

Yes, but he should be in the next class'wang'le

It's okay, and he didn't tell you to stand up.

Is it plain milk or yogurt? Isn't it sweet?

If it tastes good, ask your parents not to buy milk in the future, you have a better choice.

From a scientific point of view: unless your teacher is now breastfeeding, how can you have milk for you to drink, study hard, and make progress every day! Don't insult the teacher's name.

Do what your body instincts do.

What can you do if he doesn't want to bird you? You touch your head? Do you still care if others look at you or not? It's hot! What nerves are there without disease? Are you not wide enough to control the heavenly tube drop, is it a fever?

Indeed, think about whether you have offended him.

"Hello students! Now that the class has begun, today we are learning ... That's all I can remember.

Usually the teacher says the first thing is "class", and then the class leader shouts stand up or something.

Prepare yourself, we're going to class.

"Hello students! But it is not excluded that the teacher of the abnormal route is not ruled out, this depends on the personal characteristics!

Sit down. I had 1 class

My day, so many people came!

Okay, students be quiet.

What about the keys (a small box for the speakers)?