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Today we’re celebrating a birthday!
今天我们要庆祝一个生日!
Oh, don’t worry, Squeaks!
哦，别担心，吱吱！
It’s not my birthday.
今天不是我的生日。
It’s Sir Isaac Newton’s birthday.
今天是艾萨克·牛顿爵士的生日。
Sir Isaac Newton was a famous scientist who lived a long time ago.
艾萨克·牛顿爵士是一位生活在很久以前的著名科学家。
He was especially interested in how things move, even really big things like planets!
他对物体的运动方式特别感兴趣，甚至对行星这样的庞然大物也感兴趣。
He was also a famous mathematician.
他也是一位著名的数学家。
A mathematician is a person who uses math to tackle big questions about the world.
数学家是用数学来解决世界上重大问题的人。
Newton was born in England almost 400 years ago.
牛顿大约400年前出生于英国。
He made lots of important discoveries about the world, including figuring out that light is actually made up of all different colors.
他对世界有许多重要的发现，包括发现光实际上是由各种不同的颜色组成的。
He also helped invent a whole new type of math!
他还帮助发明了一种全新的数学!
It’s called calculus, and you can use it to learn about how things change.
这叫做微积分，你可以用它来学习事物是如何变化的。
Today, lots of people learn it in high school or college.
今天，许多人在高中或大学学习英语。
Newton made some amazing discoveries about how things move, too — everything from gigantic planets to, say … an apple.
牛顿对事物的运动也有一些惊人的发现——从巨大的行星到，比如说，一个苹果。
Are you ready for a story?
你准备好听故事了吗?
Because there’s a kind of funny one about Newton and an apple.
因为牛顿和苹果之间有一个有趣的故事。
One day, Sir Isaac Newton was at home, sitting under an apple tree in his family’s garden.
一天，艾萨克·牛顿爵士在家，坐在他家花园里的一棵苹果树下。
But then, an apple fell off the tree.
但是，一个苹果从树上掉了下来。
It might have even bopped him right on the head!
苹果甚至可能正好击中他的头!
And right then and there, Newton started to come up with one of his most important theories: the theory of gravity.
就在那时，牛顿开始提出他最重要的理论之一：引力理论。
Newton thought to himself: “Why did that apple fall from the tree?
牛顿心想:“为什么苹果会从树上掉下来?
Why didn’t it float up in the air?”
它为什么不浮在空中呢?”
We’re all pretty used to that just being the way things work:
我们都很习惯这种思维方式:
when you throw something into the air, it falls down.
当你把东西扔到空中时，它会掉下来。
But the apple got Newton thinking about why they fall down.
但是苹果让牛顿思考了它们为什么会掉下来。
And the answer he came up with was a force called gravity.
他得出的答案是重力。
A force is anything that’s a push or a pull.
力就是推或拉。
So if I pull this apple across the table, I’m putting a force on it.
所以如果我把这个苹果拉过桌子，我给它施加了一个力。
The force of gravity pulls apples, and people, and just about everything else, toward the ground.
地心引力把苹果、人和其他所有东西都拉向地面。
It’s why when we jump up in the air -- We come right back down!
这就是为什么当我们在空中跳起来的时候——我们马上就下来了!
Gravity is also why the moon goes around the Earth.
引力也是月球绕地球运行的原因。
That’s right, the same reason why an apple doesn’t float away is also why the moon doesn’t just float out into space.
没错，苹果不会漂浮的原因和月亮不会漂浮到太空的原因是一样的。
Of course, the moon isn’t actually a big apple.
当然，月球实际上不是一个大苹果。
But they’re both controlled by the same thing: gravity.
但它们都是由同一个东西控制的:重力。
Newton discovered that things that are really really heavy attract things that aren’t as heavy.
牛顿发现那些非常非常重的东西会吸引那些不那么重的东西。
Attract means when something pulls something else towards itself.
引力是指某物将另一物拉向自身。
So because the Earth is incredibly big with lots of heavy stuff inside it,
因为地球非常大里面有很多重的东西，
things like apples, and people, and just about anything else you can think of, won’t float away because the Earth is pulling them down with –
像苹果、人，以及你能想到的任何东西，都不会飘走，因为地球正在把它们拉下来
there’s that special word again – gravity!
还有一个特别的词——重力!
And since the Earth is heavier than the moon, the earth pulls the moon towards its center.
因为地球比月球重，所以地球把月球拉向它的中心。
But the moon doesn’t just crash straight into the ground!
但是月球不会直接撞向地面!
That’s because at the same time as it’s being pulled toward Earth, it’s also moving sideways.
这是因为在它被拉向地球的同时，它也在向侧面移动。
It’s kind of like the moon is trying to escape,
就像月亮想要逃离，
but since the Earth is pulling on it, it swings around and around in a circle instead.
但是因为地球在拉它，所以它就绕着一个圈转啊转。
Gravity is also why the Earth goes around the sun.
引力也是地球绕太阳运行的原因。
The sun is /muuuuuch/ heavier than the earth.
太阳比地球重得多。
It’s humongous, and if you could weigh it, it would weigh a whole lot!
它是巨大的，如果你能称它的重量，它会重很多!
So its /gravitational pull/ is a lot stronger.
所以它的引力要大得多。
Earth is pulled in and we end up going around and around the sun.
地球被拉进来，我们最终绕着太阳转了一圈又一圈。
All because of gravity!
都是因为重力!
And Newton figured out all of that when an apple fell off a tree.
牛顿在苹果从树上掉下来的时候算出了这一切。
The only thing is, although that apple story is actually pretty famous, and Newton himself used to even tell it… It may not be totally true.
唯一的问题是，尽管苹果的故事非常有名，牛顿自己也曾经讲过，但这可能不是完全正确的。
But it may not be totally un-true, either!
但这也不是完全不真实的!
The truth might be… somewhere in between.
事实可能介于两者之间。
So we do know that Newton was inspired by an apple tree,
所以我们知道牛顿的灵感来自一棵苹果树，
because a person named William Stukeley wrote a long long time ago about having a conversation with him about it.
因为很久很久以前，有一个叫威廉斯蒂克利的人写信给他，说他曾经和斯蒂克利谈过这件事。
And in this conversation, Newton mentioned watching how apples from a tree fell to Earth.
在这段对话中，牛顿提到了观察苹果是如何从树上掉下来的。
But Newton never mentioned the apple hitting him on the head.
但是牛顿从来没有提到苹果打了他的头。
That probably just got added to the story over time as people kept retelling it.
随着时间的推移，随着人们不断地复述这个故事，它可能会被添加到故事中。
We all love the apple story so much that there are apple trees that grew from that very first apple tree all over the world.
我们都非常喜欢苹果的故事，以至于全世界都有从第一棵苹果树上长出来的苹果树。
There are even special places you can go to visit these apple trees, in lots of different countries.
在许多不同的国家，甚至有一些特别的地方你可以去参观这些苹果树。
So did that apple fall from the tree and bonk Newton on the head?
那苹果从树上掉下来砸在牛顿头上了吗?
Probably not.
可能没有。
But did an apple falling from the tree to the ground inspire Newton’s theory of gravity.
但是一个苹果从树上掉到地上是否启发了牛顿的引力理论呢?
Very possibly!
很有可能！
Well, Squeaks, to celebrate Newton, what do you say we make an apple pie instead of a birthday cake?
好吧，吱吱，为了庆祝牛顿，我们做个苹果派而不是生日蛋糕怎么样?
Maybe we shouldn’t drop it to see if it falls, though!
也许我们不应该让它掉下来看看它是否会掉下来!
That would be much messier than just dropping a regular apple … plus, this way we can actually eat it!
这可比掉一个普通的苹果麻烦多了…而且，这样我们就可以吃了!
Thanks for joining us!
谢谢收看！
If you want to keep learning more about how our extraordinary world works, hit the subscribe button, and we'll see you next time here at the fort.
如果你想继续了解我们非凡的世界是如何运作的，点击订阅按钮，下次我们将在堡垒再见。
