Would you weigh less in an elevator? - Carol Hedden

Transcriber: tom carter Reviewer: Bedirhan Cinar

譯者: 盧 曉天 審譯者: Sophie Wang

You step into an elevator.

你進了電梯

It starts going down, fast.

電梯開始快速下降

What would happen if you jumped right when it started going down?

此時，如果突然往上跳 會發生什麼事？

Would the ceiling hit your head? Ouch!

會撞到天花板嗎？唉唷！

Do you stay suspended in the air while the elevator plummets down?

還是會懸在空中呢？

Let's examine the elevator problem one step at a time.

我們一步一步來剖析這個問題

First, consider a scale.

首先，想像一個體重計

You know, the kind of scale you weigh yourself on.

一般用來量體重的體重計

When you step on a scale to weigh yourself,

你站上體重計量體重時

there are two forces involved.

牽涉到兩種力

One, gravity pulls you down.

其一 是地心引力

Two, the scale pushes you up.

其二 是體重計的垂直抗力

What? You didn't know a scale could push?

什麼？ 你不知道體重計有垂直抗力？

Of course it can! If it didn't push up on you, you would go crashing through the floor.

當然！如果沒有它 體重計早被踩壞了

This upward push is called the normal force and yes, it is normally there.

這種垂直抗力叫做正向力

Since you're just standing there on the scale, you're not moving.

因為你站在體重計上，靜止不動

Therefore, you're not accelerating.

所以，你沒有加速度 根據牛頓第二運動定律

Newton's second law of motion -- net force equals mass times acceleration --

施加於物體的淨外力等於 此物體的質量與加速度的乘積

tells us that if the acceleration equals zero, the net force must equal zero.

說明，如果加速度等於零 淨外力也必等於零

Which means that the force of gravity pulling you down must be equal to the force of the scale pushing you up.

也就是說，地心引力必等於正向力

Now let's suppose you're standing on that scale in an elevator.

現在， 試想你站在電梯裡的體重計

At first, the elevator is standing still,

一開始，電梯靜止不動

so you and the scale are standing still.

正如你和體重計一樣 靜止不動

The two forces on you are equal and opposite.

在你身上的作用力相等且相反

You can read how hard the scale is pushing by looking at it.

看體重計就知道正向力有多大

We call that your weight.

也就是所謂的 體重

Then, the elevator starts falling down.

於是，電梯開始下降

You and the scale are in the elevator, so you are falling down too,

你和體重計也跟著一起下降

faster and faster.

速度越來越快

That means you are accelerating downward.

代表加速度向下

Now there is a net force in the same direction as the acceleration -- down.

此時， 有一淨外力和加速度同方向

Since gravity hasn't changed, that must mean the scale isn't pushing up as hard.

既然地心引力從未改變 代表體重計的垂直抗力不夠大

So the scale is reading a smaller number.

因此 體重計上顯示的數值較實際小

The faster the elevator accelerates, the less the scale pushes up.

由此可知，電梯下降速度越快 體重計的正向力越小

What if you jumped? Would you stop falling?

如果你向上跳呢？ 你會停止下降嗎？

Would the elevator hit your head?

還是會撞到天花板呢？

Well, what's pulling the elevator down? Gravity.

想想為何電梯會下降？ 因為地心引力

Is gravity pulling on you? Of course.

那地心引力是否也對你作用？ 當然

So your relative position in the elevator will stay the same.

所以你在電梯的位置不變

The ceiling will only hit you if you can jump up to the ceiling.

也不會撞到天花板 除非你本來就能跳到天花板

Now consider: what would happen if the elevator accelerated upward

最後，想像一下 如果電梯上升時

and, even more frightening, if someone snuck in and cut the cable holding the elevator,

突然有人發瘋， 闖進電梯井道剪斷鋼索

what would happen then?

會發生什麼事？

Think about it.

想想看 -繁體中文翻譯：盧曉天