中級 美國腔 6280 分類 收藏
開始影片後,點擊或框選字幕可以立即查詢單字
字庫載入中…
回報字幕錯誤
This is the first live cat recorded on film, and it's being dropped to solve a physics problem: Why do cats always land on their feet?
It's a question that was driving 19th century scientists nuts.
Until one of them used an unexpected tool to solve the mystery: a camera.
Étienne-Jules Marey was an obsessive scientist and inventor who analyzed how things moved.
And he started experimenting with photography at a time when the medium was mostly used to document static subjects.
But his goal was to capture motion.
And he did that by building on a basic principle of photography: exposing a photosensitive material to light and then covering it in darkness.
So his way of creating this darkness and light was to have a disc with slots in it.
By controlling the light as the subject moved across the frame, Marey was able to record movement onto a single glass plate.
Essentially, all he does is block that light intermittently.
A slot from the disc opens, and then there's darkness as the man moves, opens, darkness.
This technique is called chronophotography, and the results show something human eyes will never see on their own: individual stages of motion.
A couple of years later, Kodak introduced celluloid film and Marey updated his slot camera in a crucial way.
He swapped the single glass plate with a roll of film that moved in between exposures.
So, light: an image is made.
Darkness, the film moves on.
Light, an image — so it's a movie camera, is what it is.
Marey made a lot of films for research purposes.
And even tried dropping other animals to see if they'd land on their feet, specifically this rabbit and this chicken.
Which brings us back to the cat.
It seems to be able to right itself by flipping in the air without pushing off anything first, which would contradict the law of conservation of angular momentum.
Sounds scary, but stick with me here.
One of Newton's laws of motion says that something in motion can't just stop itself unless an opposing force acts upon it.
Basically, you can't just change direction midair, Wile E. Coyote style.
But to the naked eye, it looks like a cat can.
Most people assumed the cat was "cheating" by kicking off the hands of the person dropping it.
But Marey's film showed what's actually happening.
The first few frames prove right away that the cat doesn't start its rotation from a kick.
But what it does do is arch its back.
And by arching its back, it's divided its body into a front part and a back part, and the two parts can work independently.
You know how a figure skater pulls their arms in to rotate faster?
That's whats happening here, too.
Early in the rotation, the cat pulls its front legs in and leaves the back splayed out.
So the front half can rotate quickly while the back half stays relatively still.
Then halfway through, it does the opposite.
Front legs stretched out, back ones tucked in to flip the other half of its body around.
And you notice by the time the cat is landing, all four legs are stretched out as far as they can be, which means slow rotation.
So the cat has rotated itself, but not overall; the two halves are working in opposite ways.
It uses the inertia of its own bodyweight to spin each side.
And because the two spins operate separately in opposing directions, they cancel each other out.
So Newton's law isn't broken.
Marey published his findings in Nature in 1894, breaking down the falling cat problem for the first time.
His work remains an early example of using photography for scientific discovery.
What does photography do for science?
It records something and it makes it permanent so you can analyze it later, or so you can share it.
But what Marey did was show something that the eye could not possibly see — ever.
You might have seen another famous early example of motion photography.
In 1878, Eadweard Muybridge used 12 cameras connected to tripwires to prove that a horse lifts all four feet off the ground at some point in a gallop.
提示:點選文章或是影片下面的字幕單字,可以直接快速翻譯喔!

載入中…

載入中…

你的腳底有磁鐵吧!為什麼貓貓總是能安全落地? (Why a cat always lands on its feet)

6280 分類 收藏
Vvn Chen 發佈於 2019 年 6 月 22 日    Vvn Chen 翻譯    Evangeline 審核
看更多推薦影片
  1. 1. 單字查詢

    在字幕上選取單字即可即時查詢單字喔!

  2. 2. 單句重複播放

    可重複聽取一句單句,加強聽力!

  3. 3. 使用快速鍵

    使用影片快速鍵,讓學習更有效率!

  4. 4. 關閉語言字幕

    進階版練習可關閉字幕純聽英文哦!

  5. 5. 內嵌播放器

    可以將英文字幕學習播放器內嵌到部落格等地方喔

  6. 6. 展開播放器

    可隱藏右方全文及字典欄位,觀看影片更舒適!

  1. 英文聽力測驗

    挑戰字幕英文聽力測驗!

  1. 點擊展開筆記本讓你看的更舒服

  1. UrbanDictionary 俚語字典整合查詢。一般字典查詢不到你滿意的解譯,不妨使用「俚語字典」,或許會讓你有滿意的答案喔