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Desert Diary
Physics/Air

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The movement of the winds and the breath of life were mysteries to the ancients—and even in these days of science, remain so to many. We know, as the ancients did not, that air is composed of imaginably small particles in constant motion. Colliding incessantly with everything within range, these molecules exert pressure by the force of their collisions, and rush into areas where there are fewer molecules to knock them back. Our very breathing depends on this. Far from our actively drawing in air by expanding our chests, we merely entice the denser air of the outside to flow into the space within our lungs—air space rarefied by our enlarging rib cages. As with a lunch room at noon, the many entering dwarf the few leaving—a mass movement reversed as the back-to-work whistle sounds.

On a continental scale, the same principles produce wind and storm systems as heated and cooled air masses of different densities flow into areas of least resistance—if you're of a poetic nature, the very breathing of Mother Earth.
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Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.

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