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.

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.

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.

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.

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.

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.