Great question -- and not a simple answer! But let me try to explain.
Wind is the result of air pressure differences in the atmosphere. Across the Earth, we have areas of higher air pressure and areas of lower air pressure, and these pressure zones are always moving and changing locations over the surface of the Earth. This motion means that the pressure for any one place is always changing, even in your backyard!
Air tends to flow from areas of higher pressure toward areas of lower pressure, and that air flow is WIND.
When the difference in pressure between two pressure zones is large, then the wind tends to be strong or fast. If the difference in pressure is small, then the winds are light.
Air is a collection of molecules, a collection of gases made up of nitrogen (up to 78%), oxygen (up to 21%), water vapor (1% to 4%), and other minor gases plus particulates like dust. "High" pressure is when we pack more molecules of air gases into a space ˆ low air pressure is simply fewer air molecules in the same space.
Here's a simple example: if we blow up a balloon, we've created a pocket of high-pressure air inside the balloon. The pressure is higher inside the balloon than on the outside.
What happens if we don't tie the balloon closed? The higher pressure air inside the balloon wants to rush out of the balloon. The balloon produces a flow of air that is our own home-made version of wind.
And the high-pressure air packed inside the balloon (our homemade wind) wind will keep rushing out of the balloon until the pressure inside the balloon is the same as the pressure outside the balloon. Remember, when the balloon is deflated, it is not entirely empty ˆ it just has the same pressure as the air outside. The deflated balloon is holding the same number of molecules in the space it occupies as would be in that space if the balloon didn't exist at all.
when the pressure between two places is the same - then there is no wind at all.
Hope this helps!
WAFB Storm Team