This is gonna be really tough to see. So how are we gonna actually determine what the right answer is?
這將會非常難以觀察。所以我們要如何真正判定正確答案是什麼呢？
Ugh, if I were to drop it now, it would happen so fast you wouldn't really see clearly what's happening. So, I brought along my slow-motion camera, and you'll see it at three hundred frames per second. And it's quite spectacular.
啊，如果我要現在放手，它會發生得太快，你根本無法看清楚發生了甚麼事。所以，我帶上了慢動作攝影機，而你會在300 fps(每秒三百個畫面)的狀態下觀賞它。而那是非常壯觀的。
Well, that's ultra slow-mo. So that's exactly what we need to sort out this problem.
嗯，那就是超慢動作。所以那正是我們要解決這問題所需的東西。
Well, give it a countdown, because it happens really fast.
好，來倒數一下，因為它發生得真的很快。
Alright.
好吧。
Three, two, one, drop.
三，二，一，放手。
Wow, did you see that?
哇，你有看到嗎？
I didn't really see which happened first. I know that we need to slow that down.
我沒有真的看到哪個先發生的。我知道我們得將那放慢。
Well, let's go to slow-motion replay and see what actually happened.
好的，來調到慢動作重複播放並且看看到底發生了甚麼事。
So from the slow motion camera, we can clearly see that the bottom end stay completely stationary even after you let go at the top. It waited until the whole Slinky had collapsed down to the bottom before itself moved downwards. How do we explain that?
所以從慢動作攝影機，我們可以清楚地看到底端保持完全不動，即使在你放開頂端後。一直等到整條Slinky彈簧壓縮至底部，它本身才向下掉。那個我們要怎麼解釋呢?
Well, there are a number of explanations, but the simplest explanation is that the bottom end is sitting there minding its own business, with gravity pulling it down, and tension pulling it up. They are equal and opposite forces. No motion at the bottom end, until the bottom end gets the information that the tension has changed. And it takes time for that information to propagate down through the Slinky to reach the bottom end, so it's propagating down as a compressional wave.
這個，有一些解釋方式，但最簡單的解釋就是，底端擱置在那不多管閒事，有地心引力將它向下拉，還有張力往上拉。它們是均等且對立的力量。底端沒有動靜，直到底端得到張力改變了的訊息。而那個訊息要花時間通過Slinky彈簧向下傳導至底端，所以它是以壓縮波的方式傳導下來。
And we saw that compression wave travel down, and it has to reach the bottom before the bottom even knows that you've let go at the top.
而我們看到那個壓縮波行進而下，而且在底端實際上得知你已經放開頂端之前，壓縮波必須傳達至底部。
Correct.
正確。
And that's when it knows to start falling.
而那正是它知道要開始墜落的時候。
Correct.
正確。
That's really a remarkable finding. I mean, does this apply to any other objects, or is it just Slinkys?
那真是個非凡的發現。我的意思是，這個適用於任何其他東西嗎？還是只是Slinky彈簧條？
Now, it applies to the real world, particularly in sports, which is the field I'm interested in. For example, when a player hits a ball, there is a huge force at the business end, but that force is not felt at the handle end until the ball is well on its way. So that a wave has to propagate from the business end down to the handle end, and then it propagates back again. And what you actually felt on this end is considerably less than what the ball felt.
它適用於真實世界，特別是在運動方面，那是我感興趣的領域。舉例來說，當球員擊出一顆球，在擊球端有一股強大的力量，但直到那球已經跑得老遠，手持端才會感覺到那股力量。所以一道波必須從擊球端向下傳導至手持端，接著它再傳送回去。而你在這端所真正感覺到的遠低於球所感覺到的。
So wow, if you are playing tennis or something, you only feel that you hit the ball after you actually hit the ball.
所以哇，如果你在打網球或甚麼的，你只會在真正打到球之後，才會感覺打到球。
And the ball's nearly to the net, by the time, you actually feel what's happened.
而球幾乎已經在網邊，屆時，你才真正感覺到已經發生的事。
That goes against, you know, all your intuitions that you really can feel it as soon as the ball is on your racket.
這違反，你知道，你所有的直覺，那就是當球在你球拍上時真的可以感覺得到它。
Uh, it's the same in golf. If you whack a golf ball, you often find golfers will finish with a nice flourish, thinking that will have some effect on the ball, but of course the ball is half way to the hole by the time that happens.
啊，在高爾夫球方面也一樣。如果你揮擊一顆高爾夫球，你常會發現打者以華麗的姿勢做結，邊想著那會對球有些影響，但當然啦，在那發生的時候那顆球已經在前往球洞的半路上了。
Of course! Now, what if we want to do a little extension activity? I want you to make a prediction. If we attach this tennis ball onto the base of this Slinky, and we, ugh, drop it again, what will happen to the tennis ball? Will it do the same as the base of the Slinky and just stay there? Or will it fall with the acceleration due to gravity, uh, G? Or will it go upwards?
當然!現在，如果我們想要做些延伸活動呢？我要你預測。如果我們將這顆網球連接在Slinky彈簧條的底部，然後我們，啊，再次扔下它，網球會發生甚麼事呢？它會像Slinky彈簧底端做一樣的事、就停在那兒？還是它會因為地心引力而加速落下，啊，G力？還是它會往上跑？
Well, we'll have to try and find out.
好吧，我們必須試試看來找出答案。
Alright, I'd like you to make the prediction now. Quick.
好了，我要你們現在做出預測。快。
