Air Rush Through Narrow Space
Date: Winter 2011-2012
Why does air tend to rush in a narrow corridor or a door?
Like the Venturi of a carburetor of the older cars where the air
rushes through a narrow passage, the pressure is higher.
This is related to the relationship that Pressure = Force / Area.
The cross section of the narrow passage has a smaller area. If we
assume the force of the air is constant, then the relationship
follows that the pressure is higher.
That's the essence of why the air rushes.
There is a simple "general" answer; however, the details may be much more
complicated. Air will "rush", that is flow, from a region of high pressure
to a region of low pressure. That is the easy part, always true. The more
difficult part is why in any given set of conditions there is a pressure
difference from one place to the other.
It can be a temperature difference, a secondary flow of air -- for example a
gust of wind -- and many other possible causes. But the common factor is a
pressure difference that will tend to equalize causing the rush of air.
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Update: June 2012