82 Waterwheels and Windmills-Mid

Waterwheels and Windmills FOCUS Question How do machines use water and wind for power?

Energy in Motion We need energy! We use it to run machines, to make food, and to turn on lights. Luckily, there is energy all around us. Earth's air and water are in constant motion. This motion can be turned into energy we can use. All we have to do is capture it. Waterwheels are machines that use the power of moving water. Windmills capture the energy of moving air. For centuries, people have used waterwheels and windmills in many different ways. Today, most people use them to make electricity. How do these machines work?

Ye Old Waterwheel A waterwheel changes the energy of motion into a different kind—one that can do work. Water flowing down a river has a lot of motion energy. This energy pushes the blades of a waterwheel, causing the wheel and its axle to turn. Then the wheel and its axle can move other parts of the machine. One water-powered machine is a mill. This is a machine that grinds down grains, beans, or other hard materials. In a sawmill, a waterwheel turns sharp blades that cut logs into lumber. Some creameries still use waterwheels to run a churn that makes ice cream, cheese, or butter.

Types of Waterwheels The simplest waterwheel lies flat on its side. This is a horizontal wheel. Part of it sticks into a stream of water. The stream turns the wheel and axle. Most waterwheels are vertical, or mounted upright. As the wheel turns, its axle turns a large gear. The large gear turns a smaller gear and the smaller gear turns faster. This system changes the water's movement into mechanical energy. This is energy that can be used to do work.

There are many kinds of vertical waterwheels. Two of the most common are the overshot wheel and breastshot wheel. The turbines in modern hydroelectric dams are similar to waterwheels. Hydroelectric dams turn water energy into electricity. Word Wise A turbine is an engine powered by blades that are turned by water, wind, or steam.

Blowing in the Wind Years ago, many windmills were used to pump water out of the ground or to grind wheat. The windmill blades were tilted to catch the wind, making them turn in the breeze like a pinwheel toy. As the blades turned, they rotated an axle. This turned gears, which then moved other parts inside the machine. Most modern windmills are used for making electricity. These are called wind turbines. Their long blades spin in the wind. The energy from the moving turbines generates electricity.