Randi Ballard age 13, of City View
How is the air fixed around the earth?
Randi has a very original idea about the filmy air that surrounds our round world. Maybe it is arranged in a great hoop along the earth's orbit around the sung. The earth would stay in this filmy circle of air as it traveled along on its 600 million miles yearly path. That way we would have new air every day and leave yesterday's air behind us, That used up air would have a whole year to become fresh for us to breathe on our next trip around.
Andy says that is a very thoughtful piece of wondering and very reasonable. But the air is actually clutched in a filmy blanket around the world. It is held there by the pull of earth's gravity » the force which makes dropped things fall to the ground only a few tiny air molecules hundreds of miles above our heads ever manage to escape, These fragments must whip up speeds of almost seven miles a second in order to escape the earths big hug and such speeds are not likely,
The air higher up feels less of the earth's pull of gravity. For the farther we go from the center of a body$ the less we feel its pull. And the center of earths gravity is right in the middle of the big round balls It is not surprising: then, to learn that the thickest densest air is hugged closest to the ground. Higher up the shell of filmy air around the globe gets thinner and thinner, somewhere beyond 600 miles above our heads it finally peters out, beyond that is empty space.
This shell of filmy air travels with the earth on our yearly journey around the sun. There is no need to leave behind yesterdays used up air and take a fresh‑supply for today. For the old earth has her own tricks for keeping her blanket of air forever clean and breathable, There is always plenty of fresh air and to spare for all the plants and animals in the world.
The filmy air is washed clean by the rains the mists and the clouds. Bits of dusts dirt and smoke in the atmosphere tend to stick to cloud droplets and fall down to earth in the rapid drops.