air currents, temperature gradients and differences in pressure and

氣流，溫度梯度和在壓力差和

composition of air,

空氣的組合物，

then this is what it would look like to strike a match.

那麼這個看起來如何，像是要點火柴。

This is helium being squeezed out of a balloon.

這是氦氣從氣球中噴出來。

You could see the warm air rising off your hands.

你可以看到的暖空氣從摩擦的手中上升。

The invisible vapors of isopropyl alcohol and a plume of ejected material when you sneeze.

看不見的異丙醇汽體與打噴嚏時噴出的霧化物質。

This is the setup for how I made those shots over here

這是我如何在這裡產生這些鏡頭的設置說明

I have a 40 centimeter diameter concave parabolic mirror normally this would be used to make a telescope

我使用 通常被用於製造望遠鏡的40厘米直徑的凹拋物面反射鏡

but if it form, just a tiny piece of a big

但如果將他拓展成型，這只是大拋物鏡中很小一塊

spherical shell

對嗎？我們在一個巨大的拋物面鏡裡面

Right? A giant spherical mirror that we're inside

那麼鏡子的中心將在這裡

then the center of that mirror would be right here

而這也正是我將LED光源放在距離中心只有3毫米遠處

And that's where I've placed this led it's three millimeter

而且我塗上一些黑色指甲油，以便讓光源更微弱

But I try to make the light source even smaller by painting it with some black nail polish

所以，我們試圖產生近似於點光源的光線

so, we try to approximate a point source of light there now that light

光線從各種方向散射進來，然後從凹面鏡反射回來

spreads out in all directions, and it bounces off the mirror and reflects back

從光點看來，幾乎到精確到達同一個位置

Almost to exactly the point where the light is

你可以看到，在那裡光匯聚為一點

you can see that the light converges to a point right there

現在我展示這個光線只是一個小點，

Now I've offset the light just a little bit so that this light

而這光線將直線通過並進入我的相機鏡頭中

will pass straight through and into the lens of my camera

所以這邊，我定位這個刀片位置，

So right here, I position this razor blade,

用來切斷光線，只讓一半左右的光線通過

so it cuts off about half the light passing through

這種設置可以讓你看到鏡子前的細微變化

This setup allows you to see tiny variations in what is in front of the mirror

例如，熱空氣從蠟燭上散出

For example when you have hot gases coming off of a candle

然後，因為LED的反射光您可以看見它

Well, you can see that because as the reflected light from the led

透過熱空氣柱

Passes through this column of hot air, it

即使是很輕微的折射，都會讓光線改變方向

changes directions ever so slightly that is it refracts

探究其原因是因為

and the reason for that is because the

熱空氣的折射率和冷空氣的折射率不同

Refractive index of hot air is different from the refractive index of the cooler air

關於折射率的量度取決於光穿過介質的速度

Around it now refractive index is a measure of how fast light travels through a medium

相對於光在真空中的速度

Relative to its speed in a vacuum

因此，一般空氣中的值非常接近1，但熱空氣實測上折射率比較低

So for air the value is pretty close to 1 but hotter air actually has a lower index of refraction

在這種情況下，折射率差異是非常驚人的微小

in this case the difference in refractive index is incredibly tiny

所以我們無法注意到光線的偏轉

and so we don't notice the deflection of the light

但透過這個裝置

but with this setup

因為只有某些光線能夠通過剃刀刀鋒，所以真的可以產生差異

It actually makes a difference because some of the light that would have passed over this razor blade

透過穿越與阻擋機制，後者在影像上呈現較深色的點

Instead gets deflected down and gets blocked and that forms a darker spot on the image

就像某些光會相繼命中刀片而無法穿越

Similarly some light that would have hit the razor blade is instead deflected over

某些穿越而在影像上形成更亮的光點

it creating a brighter spot on the image and that

因為產生這樣的作用，所以你可以看到頭上的熱氣上升

is how this works, so you can see the heat rising off your head and

你可以看到自己的呼吸

You can see your breath

你可以看到冰杯澆出的冷空氣

And you can see the cold air poured out of [a] cup of ice

但溫度不是唯一影響折射率的事物

But temperature is not the only thing that affects the refractive index

不同的材料、不同的物質

different materials [different] substances

他們有不同的折射率，例如打火機裡的丁烷，很顯然我們看不到，

They have different refractive indices for example the butane in a lighter obviously we can't see that

但現在它出現了，鏡頭甚至可以在打火機點燃前呈現它

It's coming out right now, but the camera can even before the lighter is lit

當折射光通過氣泡也能呈現

light also refracts when it passes through a bubble

而光量取決於氣泡膜的厚度

and the amount depends on the thickness of that bubble film

稱為 Schlieren 的技術是出自於德國字[fli]

This technique is known as Schlieren based on the German word [flir]

這代表條紋，最早觀測到的是Robert Hooke

which means streak and it was first observed in

他在 1665年使用兩根蠟燭和一些鏡頭發現的

1665 by Robert Hooke who was using

然後在19世紀，他們利用這種方式

Two candles and some lenses then in the 19th century

這是過去使用玻璃製做鏡片時，用來找到缺陷的方法

they used this method to try to find defects and the glass used to make

以及最近人們用紋影儀研究

Lenses and more recently people have used Schlieren to study

空氣動力學和流體流動，因為它可以讓你看到在溫度梯度形成的壓力差

Aerodynamics and fluid flow because it allows you to see those pressure differences in temperature gradients

所以你可以看到衝擊波和氣體中成分的差異

So [you] can look at [shockwaves] and differences in the composition of gases

所以，當你觀看火柴點燃時，可以看到摩擦所產生的熱

So when you watch the lighting of this match you're seeing heat generated from Friction

點燃磷時這又產生更多的熱量，並產生硫和氫之間的反應

Igniting phosphorus which in turn generates more heat and begins the reaction between sulfur and potassium

你也可以看到氯酸鹽釋放出二氧化硫

Chlorate which releases sulfur dioxide which you can also see

當我吹熄火焰，你可以看到我的氣息

And you can see my breath as I blow [out] the flame [I]

設置這個作業環境讓我太興奮了

Am so excited that I got this set up to work

所以，如果你能想到任何可以利用Schlieren技術呈現的酷應用，請利用下面的評論讓我知道

So if you can think [of] anything that would look really cool in Schlieren, then let me know in the comments

我會盡量嘗試做出來，如果你是新來這個頻道，請點擊此處訂閱

And I will try [to] make [it] happen, and if you're new to this channel, [we'll] click here to subscribe

我有一些很棒的影片會盡快呈現

I've got some awesome videos coming up very soon