評(píng)論
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And lastly, here's Destin, from "Smarter Every Day,"
最后是《每天聰明一點(diǎn)點(diǎn)》的德斯丁，
talking about the conservation of angular momentum, and, since it's YouTube, cats:
為我們講述動(dòng)量守恒，由于是在YouTube上，所以他用貓來(lái)舉例：
Hey, it's me, Destin. Welcome back to "Smarter Every Day."
嗨，我是德斯丁，歡迎再次收看《每天聰明一點(diǎn)點(diǎn)》。
So you've probably observed that cats almost always land on their feet.
也許你們注意到了，貓?jiān)诼涞氐臅r(shí)候總是腳先著地。
Today's question is: why? Like most simple questions, there's a very complex answer.
今天我們就來(lái)講講這是為什么。大多數(shù)簡(jiǎn)單的問(wèn)題都有一個(gè)異常復(fù)雜的答案。
For instance, let me reword this question:
所以，我來(lái)?yè)Q一種問(wèn)法：
How does a cat go from feet-up to feet-down in a falling reference frame,
為什么貓?jiān)谝粋€(gè)下降坐標(biāo)系中，可以將四腳朝天的姿態(tài)調(diào)整為四腳著地，
without violating the conservation of angular momentum?
而又不違反角動(dòng)量守恒呢？
So, here's something all four of these videos have in common:
這四個(gè)視頻有一些共同之處：
They all have more than half a million views on YouTube.
它們?cè)赮ouTube上的觀看數(shù)都超過(guò)了50萬(wàn)。
And those are people watching not in classrooms,
雖然觀看的人沒(méi)有坐在教室里，
but because they are part of the communities of learning that are being set up by these channels.
但他們都是學(xué)習(xí)社團(tuán)的一部分，而學(xué)習(xí)社團(tuán)就是由這些（YouTube）頻道組成的。
And I said earlier that YouTube is like a classroom to me, and in many ways it is,
我之前說(shuō)過(guò)，YouTube對(duì)我而言就像教室，
because here is the instructor -- it's like the old-fashioned classroom:
因?yàn)樗淌液芟瘢欣蠋熢谥v課，就像傳統(tǒng)的課堂：
here's the instructor, and then beneath the instructor are the students, and they're all having a conversation.
老師在前面講，學(xué)生坐在下面聽(tīng)，而且他們還可以交流。
And I know that YouTube comments have a very bad reputation in the world of the Internet,
我知道YouTube的評(píng)論在互聯(lián)網(wǎng)世界里名聲非常不好，
but in fact, if you go on comments for these channels, what you'll find is people engaging the subject matter,
但實(shí)際上，如果你去看這些頻道的評(píng)論，你會(huì)發(fā)現(xiàn)人們真的在討論視頻的內(nèi)容，
asking difficult, complicated questions that are about the subject matter, and then other people answering those questions.
他們會(huì)針對(duì)視頻內(nèi)容問(wèn)各種復(fù)雜的問(wèn)題，其他網(wǎng)友則會(huì)回答這些問(wèn)題。
And because the YouTube page is set up so that the page in which I'm talking to you is on the exact
因?yàn)閅ouTube頁(yè)面是設(shè)定好的，所以我剛剛講一戰(zhàn)的那個(gè)網(wǎng)頁(yè)，
the place where I'm talking to you is on the exact same page as your comments,
會(huì)和你們發(fā)表的評(píng)論，在同一個(gè)頁(yè)面出現(xiàn)，
you are participating in a live and real and active way in the conversation.
你們參與的是一個(gè)實(shí)時(shí)的、真實(shí)的、活躍的對(duì)話。
And because I'm in comments usually, I get to participate with you.
因?yàn)槲乙步?jīng)常發(fā)表評(píng)論，所以我也跟大家一起在參與。
And you find this whether it's world history, or mathematics, or science, or whatever it is.
這些（評(píng)論）有關(guān)于世界歷史的，關(guān)于數(shù)學(xué)的或者科學(xué)的，包羅萬(wàn)象。
