what causes wind to blow ?

Wind is the air in motion. You can make your own wind by blowing air out of your mouth. It is this same principle that causes the air to blow outside. When you blow air out of your mouth the air is forced out because the space in your lungs is reduced. This causes the air in your lungs to be under higher pressure. Since there is lower pressure outside of your mouth the air will move out of your mouth. Air always moves from higher pressure toward lower pressure. As another example consider the air in a bicycle tire. A pump forces a significant amount of air into the tire. When the air is let out of a full tire you will notice it quickly comes out. It is moving from the higher pressure inside the tire toward the lower pressure outside of the tire.

The atmosphere is big. It was lots of air. There are high and low pressure systems. Think of high pressure systems as having excess air and low pressure systems having less air. Thus, the air will move from higher toward lower pressure. When it is windy outside, often there is a low pressure system the air is moving toward. How fast the wind blows will depend on the pressure differences between the high and low pressure systems. Very fast winds often occur near cold fronts, low pressure systems and jet streams. Wind can also blow faster when it is forced into a narrow space. This can happen between buildings and within mountain passes. The high and low pressure systems usually develop due to temperature differences. For this essay memorize this important concept: temperature differences result in pressure differences and this causes the air to move. This is true on all scales from the jet stream and low pressure systems to sea breeze circulations.