In ancient times, men from cultures all around the world built working kites and gliders. In China, kites shaped like birds, butterflies, and dragons were in use 2,500 years ago. Some of these ancient kites had airfoil-shaped wings. In Egypt, working model gliders more than 2,200 years old have been found. In Central America, the ancient Maya built giant, round kites for festivals.
Kite flying is still a popular activity. Every year in the city of Hamamatsu, Japan, hundreds of people fly kites during the annual kite-flying festival. In the United States, children and adults fly kites year round from windy hills, beaches, city parks, and open fields. Even the sport of hang gliding is based on kite technology. Participants strap themselves into a harness hanging below a large kite. They use the kite to ride thermals, like soaring birds do.
Kites are usually made from lightweight materials, such as wood, bamboo, paper, and fabric. Kites of all shapes and sizes stay aloft because of differences in air pressure. Air passes over the kite's upper surface, developing lift. When the lift is greater than the kite's weight, the kite rises. The air passing over the kite must be moving fast enough to créate sufficient lift. So, kites fly best on windy days.
Some kites are made with two strings attached to their frames to give the people flying the kites greater control. Pulling more on one string than the other changes the shape of the kite's surface. This change affects the forces on the kite, causing it to move. A person can make the kite move to the left or right, or make it dive and then rise again.
