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  • The next time you see a news report of a hurricane

    下次你看到新聞報導有颶風、

  • or a tropical storm

    或熱帶風暴

  • showing high winds battering trees and houses,

    強風正吹襲樹木和房屋時

  • ask yourself, "How did the wind get going so fast?"

    問問自己: 「風為什麼可以這麼快?」

  • Amazingly enough, this is a motion that started

    令人驚奇的是,這個空氣的運動

  • more than five billion years ago.

    源自於五十多億年前

  • But, to understand why, we need to understand spin.

    然而,要了解原因 我們比須了解「轉動」

  • In physics, we talk about two types of motion.

    在物理學中,我們會談論兩種運動

  • The first is straight-line motion.

    第一種是直線運動

  • You push on something, and it moves forward.

    你推某樣東西,它就向前移動

  • The second type, spin, involves an object rotating,

    第二種是轉動,涉及了物體的旋轉

  • or turning on its axis in place.

    或者說是沿著旋轉軸旋轉

  • An object in straight-line motion will move forever

    直線運動的物體,不斷向前運動

  • unless something,

    除非有像

  • like the friction of the ground beneath it,

    地板上摩擦力的這類力量

  • causes it to slow down and stop.

    讓它變慢,然後停止

  • The same thing happens when you get something spinning.

    同樣的事也發生在轉動上

  • It will keep on spinning until something stops it.

    旋轉會持續到有力量將它停下來

  • But the spin can speed up.

    但旋轉也可以加速

  • If an ice skater is gliding across the ice

    如果溜冰的選手沿著直線

  • in straight-line motion and she pulls her arms in,

    滑過冰場,然後把手臂收回來

  • she keeps on gliding at the same speed.

    她會以等速繼續滑行

  • But if she is spinning on the ice

    但如果她是在冰上轉動

  • and she pulls her arms in,

    然後把手臂收回來

  • you know what happens next.

    你很清楚會發生什麼事

  • She spins faster.

    ──她會轉得更快

  • This is called the conservation of angular momentum.

    這叫做「角動量守恆」

  • Mathematically, angular momentum is a product of two numbers,

    數學上,角動量是兩個數的相乘

  • one that gives the spin rate

    一個是轉動的速度、

  • and one that gives the distance of the mass from the axis.

    一個是質量到旋轉軸的距離

  • If something is freely spinning,

    所以當物體自由轉動時

  • as one number gets bigger,

    一個數字變大

  • the other gets smaller.

    另一個就變小

  • Arms closer, spin faster.

    當手收回來,就轉得快

  • Arms farther, spin slower.

    當手伸出去,就轉得慢

  • Spin causes other effects, too.

    轉動還會造成其他效應

  • If you are riding on a spinning merry-go-round

    如果你騎著旋轉木馬

  • and you toss a ball to a friend,

    然後朝著朋友丟球

  • it will appear to follow a curving path.

    看起來球的路徑是曲線

  • It doesn't actually curve, though.

    但其實並不是

  • It really goes in a straight line.

    它走的是直線

  • You were the one who was following a curving path,

    你才是沿著曲線運動的人

  • but, from your point of view,

    但從你的角度看

  • the ball appears to curve.

    球變成了曲線運動

  • We call this the coriolis effect.

    這種現象叫做「科氏力效應」

  • Oh, and you are riding on a speeding merry-go-round

    你正坐在超高速的旋轉木馬上

  • right now at this very moment.

    就在此時此刻

  • We call it the Earth.

    它叫做地球

  • The Earth spins on its axis once each day.

    地球沿著地軸,每天自轉一圈

  • But why does the Earth spin?

    但為什麼地球會轉動?

  • Now, that's a story that starts billions of years ago.

    這是幾十億年前的故事了

  • A cloud of dust and gas that form

    有一團灰塵氣體雲

  • the Sun and the Earth and the planets

    形成太陽、地球、行星、

  • and you and me

    和你我

  • started to collapse as gravity pulled it all together.

    重力把它們拉在一起,並開始坍塌

  • Before it started to collapse,

    在坍塌前

  • this cloud had a very gentle spin.

    這片雲緩慢的轉動著

  • And, as it collapsed,

    在坍塌時

  • like that ice skater pulling her arms in,

    就像溜冰選手把手收回一樣

  • the spin got faster and faster.

    轉動變得越來越快

  • And everything that formed out of the cloud,

    而所有這雲形成的星體:

  • the Sun

    太陽、

  • and the planets around the Sun

    圍繞太陽的行星、

  • and the moons around the planets,

    圍繞行星的衛星

  • all inherited this spin.

    都繼承了這股轉動力量

  • And this inherited spin is what gives us night and day.

    就是這個轉動 讓我們有了白天與黑夜

  • And this day-night cycle is what drives our weather.

    日夜循環讓我們有各種天氣

  • The Earth is warm on the daytime side,

    地球上白天的那面較暖

  • cool on the nighttime side,

    夜晚的那面較涼

  • and it's warmer at the equator than at the poles.

    赤道也比南北極溫暖

  • The differences in temperature

    這些溫度上的差異

  • make differences in air pressure,

    造成氣壓不同

  • and the differences in air pressure

    而氣壓的不同

  • make air move.

    造成了空氣的流動

  • They make the wind blow.

    造成了風

  • But, because the Earth spins,

    但由於地球在旋轉

  • the moving air curves to the right

    北半球的空氣運動

  • in the Northern Hemisphere

    會向右偏成曲線

  • because of the coriolis effect.

    這是科氏力的緣故

  • If there's a region of low pressure in the atmosphere,

    如果大氣層中有一區低壓

  • air is pushed toward it,

    空氣就會流進來

  • like water going down a drain.

    像是水流進排水管

  • But the air curves to the right as it goes,

    但空氣運動時會向右偏

  • and this gives it a spin.

    這就造成了旋轉

  • With the dramatic low pressure in a storm,

    由於風暴中心的超級低壓

  • the air gets pulled in tighter and tighter,

    空氣吸進來的力量越來越強

  • so it gets going faster and faster,

    風速就越來越快

  • and this is how we get the high winds of a hurricane.

    這就是颶風的風速極快的原因

  • So, when you see a spinning storm on a weather report,

    看到氣象報導上旋轉的風暴時

  • think about this:

    想想看:

  • The spin ultimately came from the spin of the Earth,

    風暴的轉動源自於地球的轉動

  • and the Earth's spin is a remnant,

    地球的轉動是種遺跡、

  • a fossil relic,

    化石級的遺跡

  • of the gentle spin of the cloud of dust and gas

    源自於一團灰塵氣體雲

  • that collapsed to make the Earth

    坍塌形成地球

  • some five billion years ago.

    時間是五十億年前

  • You are watching something, the spin,

    你看到的現象──轉動

  • that is older than dirt,

    比塵埃還古老、

  • that's older than rocks,

    比岩石還古老、

  • that's older than the Earth itself.

    比地球本身還古老

The next time you see a news report of a hurricane

下次你看到新聞報導有颶風、

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B1 中級 中文 TED-Ed 地球 運動 空氣 曲線 風暴

【TED-Ed】為什麼地球會轉動 (What on Earth is spin? - Brian Jones)

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    Zenn 發佈於 2013 年 10 月 29 日
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