Why Do We Pass Wind?

Ok, so we've got when it happens and why it sounds that way, and a generality of contributing factors, so now lets get into the actual 'why'...
 'Passing wind' is merely the release of gases from the intestines (well, by the time it's released, it's only in the large intestines) and colon.
 But how does it get there? That's a more complex question. As you probably know, during the digestive process, the food you eat passes through the stomach where it gets churned and mixed with stomach acids and digestive juices produced by the stomach (more or less), then passes into our intestinal track... Well, what happens in that region? We know that food passes into our bodies as nutrition, but how? Are there little chomping mouths in there (like some children's marble capturing game)? Well, no. The reason our stomach churns the food and mixes it with the digestive juices is to start it breaking down into it's basic components (and for it to become very small particles in the process), as well as involving a great deal of enzymatic processing that finally breaks down the nutritive foodstuffs to the types and size we need for our cells to carry it into our circulatory system and nourish the body... That's all well and good, but that's not the problem, and certainly not the cause of our ill-fated 'wind'...
THAT is caused by further processing of the parts that we often can't fully break down early on in the digestion process, and the small amounts of air that we regularly swallow while drinking, with excessive swallowing (possibly due to nausea, or sometimes acid reflux and heartburn)... Of course any amount of air that we swallow that is not 'burped' out, has to go somewhere... Mix that with the gases produced in the large intestines by various enzymes breaking down (or trying to) of those parts of the (now ex-)foodstuffs, as well as fermentation by yeasts... The pressure builds as it passes through our large intestines in much the same way that wastes do, until as described in the first answer, the pressure becomes more than you want to stand... And >Presto!< ...The gas we pass... And THAT sukhraj is WHY we pass wind...
 I hope my answer has in some way helped 'clear' the air, so to speak...
(^_^)  Have a great day!

Wind is an air current,moving with speed in any direction.As well as currents of air that flow across the earth's surface,there are upward and downward currents of air.A variety of conditions give rise to these winds,particularly land and sea breezes,which affect the coastal and lake side areas.These breezes are the result of the different rates at which land and water bodies heat up and cool down.This produces local pressure changes,and thus deermine the direction of these winds.Wind has an important effect on air temperature .This is known as the chill factor, which causes the wind to make the air feel colder.

The amount of heat absorbed by the earth's surface varies from place to place.In high latitudes the sun rays have to pass through a greater thickness of atmosphere and they also spread out over a larger area.It is the equator where the sun rays are most concentrated .Here the heated air expands and rises,creating a low pressure area into which trade winds blow from north and south.The doldrums is the name given to the area of low pressure around the equator.It is marked by calms:sailing ships tried to avoid the doldrums because they might be stationary for days at a time.
As it rises and spread north and south,the warm air from the equator cools.Around latitudes 30 degrees north and 30 degrees south (the Horse Latitudes),it finally sinks back to form an area of high pressure.From the Horse Latitudes some of the air flows back to the equator,and some flows towards the poles as winds known as the westerlies.These relatively warm westerlies finally meet cold,dense air flowing from the north and souh poles .In these ways the winds redistribute heat around the earth's surface. As the map of the world's major wind belts shows,the air currents do not flow in a north-to-south direction.Instead ,they are deflected by the Coriolis Force,caused by the earth's rotation on its axis from west to east.This has the effect that winds and ocean currents in the northern Hemisphere are deflected to the right of the direction in which they are moving.The opposite occurs in the southern hemisphere.The Coriolis Force ,therefore ,is responsible for the north-east and southe-east trade winds,the north-westerlies and south-westerlies and the polar easterlies.

Well expulsion of flatus when your rectum relaxes is what results in the passing of the wind. When the concentration of flatus becomes too great for your anal spincter muscles to withhold it releases all the gases contained. The noise created as a result sometimes depends on the size and position of the buttocks and is caused by the vibration of the anal spincter muscles. It can be reduced however by changing your dietary habits and exercising more. Flatulence.