時差N小時:神奇的慣性力

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唐：雅艾爾，看見這杯裝滿水的玻璃杯嗎?

Yael: Yes.

雅艾爾：是的。

Don: Watch me swing it around my head!

唐：看我讓它在我頭上擺動!

Yael: Look out!!!...Hey, how did you do that? Youswung the glass completely around without spilling adrop.

雅艾爾：小心!!!...嘿，你是怎么做到的?你把杯子完全倒過來了，卻沒有灑一滴水。

Don: Not bad, eh? Want to try it?

唐：不錯吧?想不想試試?

Yael: Not until I know the secret.

雅艾爾：告訴我其中的奧秘我就試。

Don: The secret is centrifugal.

唐：奧秘就是離心。

Yael: You mean centrifugal force? I thought that was a myth.

雅艾爾：你是指離心力嗎?我還以為那是神話。

Don: It's no myth, though it is what physicists call a "fictitious force."If you tie a rock to astring and spin it around, it feels as though some force is trying to drive the rock away fromthe center of the spin. What you're actually feeling, though, is just the rock's inertia.

唐：不是神話，在物理學上我們叫它“慣性力”。如果你用繩子綁住一塊石頭旋轉(zhuǎn)，就會感到有一股力量驅(qū)使石頭偏離旋轉(zhuǎn)中心。你感受到的力實際上是石頭的慣性力。

Yael: Hmmm...better explain that.

雅艾爾：嗯...最好解釋一下慣性力。

Don: Well, the law of inertia says that something in motion will tend to stay in motion, andwhat's more, to move in a straight line. The rock is set into motion and is trying at everymoment to leave the circle and move away in a straight line. The string is keeping it fromdoing so, which is why it feels like a mysterious force is pushing the rock away.

唐：好吧，慣性定律提出運動的物體都具有保持其運動狀態(tài)不變的特性，并且沿著原來的軌跡做直線運動。石頭運動時，總是時刻傾向于以直線運動，偏離圓形軌跡。繩子阻止了石頭偏離，這就是感覺有一股神秘的力量在拉走石頭的原因。

Yael: I get it. So when you spin the glass over your head, the water inside it is trying to moveoff in a straight line too. But the glass prevents it from doing so, as long as you keep thebottom of the glass pointed away from yourself. Inertia holds the water inside the spinningglass!

雅艾爾：我明白了。所以說當玻璃杯轉(zhuǎn)過頭頂時，杯里的水也同樣傾向于做直線運動。但只要你保持將杯底指向自己，玻璃杯就會阻止水的偏離。慣性使水留在旋轉(zhuǎn)的杯子里。

Don: Right. Let's try again.

唐：對。再來試一試。

Yael: I think our listeners better practice this one outside at first.

雅艾爾：我認為，聽眾最好先在外面實踐一次。