32 A2+ the wheel

CHAPTER 1 Inventing the Wheel IT'S A MAN-MADE INVENTION, IT HAS COMPLETELY CHANGED THE WAY WE LIVE, AND IT'S EVERYWHERE IN THE WORLD. WHAT IS IT? THE WHEEL! Wheels are all around us. You use them every day, but you probably don't think about them very often. In fact, the wheel as we know it is quite a new invention. There are no real wheels in nature. There aren't any animals that use wheels to get around. But why not? Why are there no animals with wheels instead of legs? Perhaps because wheels aren't any good on some kinds of ground. It's hard to cross the desert or the forest or to climb a mountain on wheels. However, for humans, the wheel has been an amazing invention.

第一章发明轮子这是一项人造的发明，它完全改变了我们的生活方式，而且它在世界上无处不在。 这是什么？轮子!我们周围到处都是轮子。 你每天都在使用它们，但你可能不会经常想到它们。 事实上，正如我们所知，轮子是一项相当新的发明。 自然界中没有真正的轮子。 没有任何动物用轮子四处走动。 为什么不呢？为什么没有动物用轮子代替腿呢？ 也许是因为车轮在某些地面上不太好用。 骑着车穿越沙漠、森林或爬山都很困难。 然而，对于人类来说，轮子是一项了不起的发明。

If there are no wheels in nature, how did people first make them? Nobody really knows the answer. There are many round shapes and circles in nature, but they aren't like wheels; they aren't used to help move things. The earliest people worked with stone. So, maybe they saw round stones rolling. But they also made boats from wood. Perhaps they saw the logs they used for building boats rolling down a hill! One of the earliest uses of logs to move things was in Egypt about 3000 BCE. Logs were used to build the pyramids. The heavy stones for these buildings were put on flat sleds and pulled forward over logs, called rollers. The rolling logs helped move the stones more easily.

如果自然界没有轮子，那么人类最初是如何制造轮子的呢？ 没有人真正知道答案。 自然界中有许多圆形和圆圈，但它们不像轮子；它们不是用来帮忙搬东西的。 最早的人们用石头工作。 所以，也许他们看到圆形的石头在滚动。 但他们也用木头做船。 也许他们看到了用来造船的原木滚下山！最早使用原木搬运物品的一次是在公元前3000年的埃及。 圆木被用来建造金字塔。 用于建造这些建筑的沉重的石头被放在扁平的雪橇上，在被称为滚轮的圆木上向前拉。 滚动的圆木有助于更容易地移动石头。

The first real wheels were probably made in Mesopotamia, now Iraq. But scientists think that those first wheels were not used for moving a vehicle. They were used in pottery wheels. These machines turned quickly in a circle to help people make things like cups and bowls. Another early wheel, a millstone, was a heavy, round stone. It was used for breaking down plants for cooking and for making flour. The earliest pictures of wheels on vehicles are on Mesopotamian paintings from 3000-2700 BCE. These wheels were made of solid wood and turned on a simple axle. Around 2000 BCE the Egyptians started using spokes on their chariot wheels. These wheels needed less wood, so they were cheaper to make. They were also much lighter and could travel faster.

第一个真正的轮子可能是在美索不达米亚，也就是现在的伊拉克制造的。 但科学家们认为，最初的轮子并不是用来移动车辆的。 它们被用在陶轮上。 这些机器很快转了一圈，帮助人们制作杯子和碗之类的东西。 另一种早期的轮子，磨石，是一种又重又圆的石头。 它被用来分解植物来烹饪和制作面粉。 最早的车轮图片出现在公元前3000-2700年的美索不达米亚绘画上。 这些轮子是由实木制成的，在一个简单的轴上转动。 大约公元前2000年，埃及人开始在他们的车轮上使用辐条。 这些轮子需要的木材更少，所以制造成本更低。 它们也更轻，可以走得更快。

The wheel was soon used by different groups of people across Europe and Asia. By 500 BCE, many types of wheeled vehicles were in use, from fast chariots to large, slow carts. The wheels they used are much like the wheels we use today. However, in other places in the world, wheels were never used. Central and South American peoples, like the Mayans or Incas, built amazing cities and temples without using wheels. Nobody knows why, but it may be because they lived in mountainous areas, where it was impossible to use wheeled vehicles. Wheels are no good in high mountains, in deep snow, or in desert sands. Even today in the Sahara desert, animals like the camel are more useful than wheeled vehicles.

这个轮子很快就被欧洲和亚洲的不同群体使用。 到公元前500年，许多类型的轮式交通工具都在使用，从快速的战车到又大又慢的大车。 他们用的轮子和我们今天用的轮子很像。 然而，在世界上的其他地方，轮子从未被使用过。 中美洲和南美洲的人们，如玛雅人或印加人，不用轮子就建造了令人惊叹的城市和寺庙。 没有人知道为什么，但可能是因为他们生活在山区，在那里不可能使用轮式车辆。 在高山、深雪或沙漠中，轮子都不好用。 即使在今天的撒哈拉沙漠，像骆驼这样的动物也比轮式车辆更有用。

CHAPTER 2 Making Wheels Work THE WHEEL IS BEST KNOWN FOR ITS USE IN VEHICLES, BUT IT WAS FIRST USED IN INDUSTRY. Throughout history machines have used wheels. And for a long time wheels also made machines work. The first wheel used for power was the waterwheel. This was a great improvement in technology because it let people use running water to power machines instead of using animals or other people. The first waterwheel we know about was in a flour mill in Byzantium, now Turkey. The first waterwheels lay on their sides. But by 240 CE, in Alexandria in Egypt, people were using wheels that stood up in rivers and were much more powerful.

车轮以其在车辆上的用途而闻名，但它最初是在工业上使用的。 纵观历史，机器一直使用轮子。 在很长一段时间里，轮子也使机器运转起来。 第一个用来发电的轮子是水车。 这是技术上的一大进步，因为它让人们可以使用自来水来驱动机器，而不是使用动物或其他人。 我们所知道的第一个水车是在拜占庭的一个面粉厂，现在的土耳其。 第一批水车侧躺着。 但到了公元240年，在埃及的亚历山大港，人们开始使用立在河里的轮子，这种轮子的动力要大得多。

To use waterwheels to drive machines, people needed a way to send the power from the turning wheel to the things they wanted to work on. They used more wheels! They found that if you cut teeth into two wheels and put them together, the first wheel turns the second one. As early as 330 BCE, the Greek writer Aristotle talked about toothed wheels, called gears. He realized that when the teeth from the first wheel push the second, the second wheel turns in the opposite direction. But a third wheel moves opposite to the second, in the same direction as the first one. By putting gears together, you can send the power from a waterwheel to a machine. The Greeks used gears to make complicated mechanisms like clocks.

为了用水轮驱动机器，人们需要一种方法把轮子的动力输送到他们想做的事情上。 他们用了更多的轮子！他们发现，如果你把牙齿切成两个轮子，然后把它们放在一起，第一个轮子会带动第二个轮子。 早在公元前330年，希腊作家亚里士多德就谈到了有齿的轮子，称为齿轮。 他意识到，当第一个轮子的齿推动第二个轮子时，第二个轮子就会朝相反的方向转动。 但第三个轮子的运动方向与第二个相反，与第一个方向相同。 通过把齿轮放在一起，你可以把动力从水车送到机器上。 希腊人用齿轮制造复杂的机械装置，如钟表。