Wind
Air is a mixture of gases (mainly oxygen and nitrogen ).
You cannot see air, but you can feel it.
You feel the air when it moves.
Air that moves is called wind .

Wind is created by the thermal energy of the sun.
The sun heats up the earth and the air above it.
The hot air rises.
There is less air where it rises.
Air from somewhere else flows towards that spot.

Windmills use the wind.
Windmills used to be used to mill grain.
People also sailed the seas.
Now we use wind mainly to make electricity .