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  • So, this

    所以,這個

  • 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'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

  • 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。

  • nopeno 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。

So, this

所以,這個

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