Caption: Wind farm in California
Very long ago, people used the power of wind to sail boats. About 1,200 years ago, the first windmills we know about were being used in Persia. Windmills may have been used in China even before that. The first windmills were used to grind grain. Later, windmills were used to pump water. They were used to irrigate crops. They were used to drain flooded land.
Windmills are machines. Windmills change wind energy into mechanical energy. The "blades" on windmills are called sails. They work much like the sails on boats. On the first windmills, grinding stones were fastened to the vertical shaft holding up the windmill's sails. A structure was built for the grinding equipment. The walls of the building blocked the wind so that it didn't drag on the grinding stones and slow them down. The first sails (in Persia) were made of bundles of reeds or wood. These bundles were attached to the vertical shaft. The wind turned the sails. This caused the vertical shaft to turn, and this caused the grinding stones to turn. As the stones turned, the grain was ground into flour or corn meal.