is an airplane here

這裡有飛機

ok, so you probably already knew that

好吧，所以你可能已經知道，

if you've flown in one or maybe you've just seen them fly

如果你曾經坐在一架飛行中的飛機裡，或者也許你只是看到他們飛行

but even if you've seen them or been in one

但是，即使你見過飛機或曾經搭乘過

do you know how they work? Is it magic?

你知道飛機是如何飛在空中的嗎？是魔法嗎？

wingardium leviosa!

飛起來吧!(哈利波特咒語)

Are there invisible fairies that hold the plane aloft?

是否有隱形的仙女將飛機託舉起來？

Alright men we've got a busy morning and lots of flights to carry

好了，夥計們，我們早上很忙，有很多班機要飛。

or is it science?

還是科學？

Well, you guessed it the answer is indeed: science

好吧，你猜對了，答案確實是：科學。

That's ridiculous!

太荒謬了！

What?

什麼？

so to discuss how airplane flies we first have to talk about the forces on

所以要討論飛機是如何飛行的，我們首先要討論飛機上的力。

an airplane

飛機

which pushed around and all sorts of different directions

它推來推去，各種不同的方向。

Now we're gonna focus on airplanes today

現在，我們今天要關注的是飛機。

because they're awesome

因為他們很棒

most of these courses apply to any other vehicle

這些課程大多適用於任何其他車輛

The first force acts on all these vehicles

第一股力量作用於所有這些車輛

really it acts on everything

真可謂無所不用其極

it's the weight force, which points down

這是重量的力量，它指出了下來

towards the center

向中心

of Earth

地球的

Weight

重量

is equal to the mass of the airplane m, right here, times acceleration due

等於飛機的質量m，就在這裡，乘以加速度，由於。

to gravity. Here on earth

重力造成。在地球上

g is equal to 9.81

g等於9.81

meters per second squared

米/秒平方

now that's only for earth

那只適用於地球

the acceleration due to gravity really depends on the mass of the planet

由重力引起的加速度實際上取決於你位於的星球的質量。

that your on

您在

the larger the planet the higher the gravity

星球越大，重力越大

so, 9.81 meters per second squared here on earth. On the moon

所以，在地球上是9. 81米/每秒平方。然而在月球上

however is smaller than earth so the acceleration due to gravity is only

，由於比地球小，所以重力造成的加速度只有

one sixth

六分之一

that on earth - one point six meters per second squared

秒鐘點六米

this is why astronauts can bounce high on the moon

這就是為什麼太空人能在月球上高高彈起的原因。

but not on earth

不在人間

this isn't nearly as much fun

這不是那麼好玩的

obviously there has to be another force opposing the weight and pushing the

顯然，必須有另一種力量來對抗重量，並推動

airplane up

飛機

this force

這種力量

is called lift

稱為升降機

Lift operates perpendicular

電梯垂直運行

to the airplane's wings, which are

到飛機的翅膀，這是

right here in the side view

在這裡的側視圖

now

現在

if these are only two forces our aircraft will be able to go up and down

如果只有這兩股力量，我們的飛機就能上天入地了

but it won't go anywhere so we have to have a force that pushes the airplane forward

但它不會去任何地方，所以我們必須有一個力量，推動飛機前進。

and this

而這

is called thrust

稱為推力

all vehicles have thrust otherwise

車到山前必有路

they wouldn't go anywhere like our airplane

他們不會像我們的飛機一樣去任何地方。

Why didn't you buy a car with thrust?

你為什麼不買一輛帶推力的車？

I'm sorry. We can at least roll down the hill

我&#39；對不起。我們至少可以從山上滾下來

On the aircraft this thrust is produced by engines

在飛機上，這種推力是由發動機產生的。

There are two main types of engines

主要有兩種類型的發動機

we have propellers like this little guy right here

我們有像這個小傢伙一樣的螺旋槳，就在這裡。

and jet engines, like our first model

和噴氣式發動機，比如我們的第一個模型

Whatever the type of engines, they all work by the same principle

無論哪種類型的發動機，它們的工作原理都是一樣的。

So we draw a little

所以我們畫了一個小

side view of an engine here

側面圖

The engines excelerate air

發動機的空氣性能優異

out the back

背後

this direction

這邊

and by newton's

和牛頓的

third law

第三定律

there's an equal and

勢均力敵

opposite reaction and that's the thrust force

反作用力，這就是推力

pushing the aircraft forward

推進器

this is really the same thing that happens when you blow up a balloon and

這真的是同樣的事情，當你吹氣球和

you let it go. The air comes out the back and the balloon

你讓它去。空氣從後面出來了，氣球

moves forward

前進

We have a force that opposes the

我們有一股力量，反對

thrust - it's called drag and it points opposite

推力--這叫阻力，它指向相反的方向

the direction of flight

飛行方向

The major type of drag is pressure drag which is the force caused by the air

主要的阻力類型是壓力阻力，它是由空氣引起的力。

smacking into the airplane

撞上飛機

so we try to minimize this type of drag by making the airplane as

所以我們儘量減少這種類型的阻力，使飛機儘可能地減少。

aerodynamic as possible

儘可能的空氣動力學

that means that has smooth lines

那就是線條流暢

in the air flows nice and cleanly the over the front here

在空氣中流淌著漂亮而乾淨的前面這裡。

you can feel the pressure drag when you stick your hand out the window moving car

當你把手伸向窗外的汽車時，你可以感覺到壓力的拖累。

uh...

呃...

honey your hand

蜜糖手

you hand please

伸手

when your hand is horizontal it's aerodynamic and you really don't feel a

當你的手是水準的，它'的空氣動力學，你真的不覺得'。

lot of drag. But if you slowly turn your hand vertical

很多的阻力。但如果你慢慢地把你的手豎起來

you can really feel the drag increasing

你可以真正感受到阻力的增加

So these are four forces on the airplane

所以這四種力量在飛機上

But perhaps you're thinking:

但也許你'在想。

so this really cool and everything

所以這真的很酷，一切

but how do we increase and decrease the airplane's lift to move up and down

但我們如何增加和減少飛機的升力，使其上下移動。

that's a great question

這是個好問題

Well, let's look at the equation for the magnitude of lift per unit wing

好吧，讓我們來看看組織、部門機翼升力大小的公式吧

area. We'll call that L

地區。我們就叫它L

L equals

L等於

one-half

半

times rho times C_L times v squared

乘以rho乘以C_L乘以v的平方

it's that simple

就這麼簡單

okay okay okay I'll tell you what each of these means

好吧好吧好吧，我告訴你這些都是什麼意思。

so rho, it's not a "p", it's the greek letter rho

所以rho，它不是一個"p"，它&39;是希臘字母rho。

rho is the density of the air which is a measure of the number of air

rho是空氣的密度，它是空氣數量的衡量標準。

molecules in a certain volume

體積

density of the air varies with altitude and temperatures

空氣密度隨海拔和溫度變化而變化

so as you go higher up

越往上

there the air is thinner and so the density is lower

那裡的空氣更稀薄，所以密度更低。

if we want to simplify things we generally use the standard density

如果我們想簡化事情，我們一般會使用標準密度

which is 1.2754

即1.2754

kilograms

公斤

per meters cubed

每米立方

v, here, is the speed of the aircraft or how fast it's traveling

v，這裡指的是飛機的速度或者說是它的行駛速度。

and C_L is something called the coefficient of lift

而C_L是一種叫做升力係數的東西。

it's a number of that gives us some information about the shape of the

它'的數量，給我們提供了一些關於形狀的資訊。

aircraft's wings

機翼

these things right here

這些東西

the coefficient of lift changes with the angle of attack. Angle of what?

升力係數隨攻角而變化。什麼角度？

Aircraft can pitch up

飛機可以俯仰

and down. And even if their pitched up

和下降。即使他們的投擲了

they're still travelling

他們還在旅行

in a horizontal direction like that

水準方向

now

現在

the angle formed here by the horizontal direction of travel

角度

and the direction of the aircraft's nose

和飛機機頭的方向'。

is called the angle of attack. And we denote that with the greek letter

被稱為攻擊角。我們用希臘字母來表示

alpha

阿爾法

so you can make a little

所以你可以做一點

plot here of that. We're gonna put coefficient of lift

這裡的情節。我們要把升力係數 We''re gonna put coefficient of lift

up on the y axis and the angle of attack

在y軸上向上，攻角

down on the x axis

在X軸上向下

so as the airplane starts to pitch up

所以，當飛機開始傾斜起來

If I can get a hand here Thank you.

如果我能幫上忙的話，謝謝你。

as the aircraft starts to pitch up

當飛機開始俯衝時

the coefficient of lift increases

升力係數增加

this is a good thing because

這是件好事，因為

we have more lift

我們有更多的提升

as we continue to increase we eventually reach a point

愈演愈烈，最終達到

where we keep pitching up but

在那裡，我們繼續投擲了，但

the left starts decreasing

向左

this is something called

這就是

stall

攤位

and it's

和它'的

it's not a good thing

不吉利

so hot we generally avoid pitching up this much

這麼熱的天氣，我們一般都不會投這麼多的錢

there's a similar equation for the drag per unit wing area: D

有'組織、部門翼面積阻力的類似公式。D

D equals 1/2 rho

D等於1/2rho

not C_L - that really wouldn't make any sense

而不是C_L--那真的不會有任何意義。

C_D

C_D

as you can guess it's the coefficient of drag

你可以猜到它的阻力系數。

times the velocity squared

乘以速度的平方

the coefficient of drag is - it's another number that tells us something about the

阻力系數是--它是另一個數字，告訴我們一些關於

wings

翅膀

and it also varies

而它也變化

with the angle of attack, so as the angle of attack increases (oh, thank you)

隨著攻角的增大，所以隨著攻角的增大(哦，謝謝你)

the coefficient of drag increases as well. Thank you very much

阻力系數也會增加。謝謝你

this

這個

is because

是由於

as the aircraft is pitching up

俯仰時

there is more wing area perpendicular

翼面垂直

to the flow

對流

Now, this reminds me of something that we talked about earlier

現在，這讓我想起了我們之前說過的一些事情。

exactly this is very similar to whenever you hold your hand

正好這就跟你握手的時候很像。

out the window of a car

車窗外

and so

諸如此類

that's

那是

pretty much everything you need to know about how an aircraft flies

幾乎所有你需要知道的關於飛機如何飛行的事情。

so the next time your on an airplane or

所以下一次你在飛機上或

you just see one

你只看到一個

you can really know exactly what it is that's keeping it up in the air

你可以真正知道它到底是什麼，'的保持它的空氣。

nope… no it's not them either

不......不，也不是他們

ah... there you go now you got it

啊... ... 你去那裡 現在你得到了它。