Energy from moving air

How uneven heating of water and land causes wind
Image of how uneven heating of water and land causes wind. 

Land heats up faster than water.

Warm air over the land rises.

Cool air over the water moves in.

Source: Adapted from National Energy Education Development Project (public domain)

Wind is caused by the uneven heating of the earth's surface by the sun. Because the earth's surface is made of different types of land and water, it absorbs the sun's heat at different rates. One example of this uneven heating can be found in the daily wind cycle.

The daily wind cycle

During the day, the air above the land heats up faster than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating wind. At night, the winds are reversed because the air cools more rapidly over land than over water.

In the same way, the atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North Pole and the South Pole.

Wind energy for electricity generation

Today, wind energy is mainly used to generate electricity, although water pumping windmills were once used throughout the United States.