时差N小时:神奇的惯性力

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唐：雅艾尔，看见这杯装满水的玻璃杯吗?

Yael: Yes.

雅艾尔：是的。

Don: Watch me swing it around my head!

唐：看我让它在我头上摆动!

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

雅艾尔：小心!!!...嘿，你是怎么做到的?你把杯子完全倒过来了，却没有洒一滴水。

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

唐：不错吧?想不想试试?

Yael: Not until I know the secret.

雅艾尔：告诉我其中的奥秘我就试。

Don: The secret is centrifugal.

唐：奥秘就是离心。

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

雅艾尔：你是指离心力吗?我还以为那是神话。

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：不是神话，在物理学上我们叫它“惯性力”。如果你用绳子绑住一块石头旋转，就会感到有一股力量驱使石头偏离旋转中心。你感受到的力实际上是石头的惯性力。

Yael: Hmmm...better explain that.

雅艾尔：嗯...最好解释一下惯性力。

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，惯性定律提出运动的物体都具有保持其运动状态不变的特性，并且沿着原来的轨迹做直线运动。石头运动时，总是时刻倾向于以直线运动，偏离圆形轨迹。绳子阻止了石头偏离，这就是感觉有一股神秘的力量在拉走石头的原因。

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!

雅艾尔：我明白了。所以说当玻璃杯转过头顶时，杯里的水也同样倾向于做直线运动。但只要你保持将杯底指向自己，玻璃杯就会阻止水的偏离。惯性使水留在旋转的杯子里。

Don: Right. Let's try again.

唐：对。再来试一试。

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

雅艾尔：我认为，听众最好先在外面实践一次。