The Journey of Flight.pdf - Valkyrie Cadet

Weight is in one direction, while pressure is in all directions—both decrease when altitude increases.
than it, the air temperature drops below its dew point and the vapor condenses into a liquid and the wall
or ceiling becomes wet.
Evaporation of water on a global scale takes place in a manner similar to the example above, but
it is much subtler. Most of the water vapor in the atmosphere comes from the oceans and other large
bodies of water. A process called solar radiation heats the water causing the evaporation. The warm
moist air moves over cooler land and cools below its dew point causing the excess water vapor to fall
back to the ground in some form of precipitation.
Another method of putting water vapor into the atmosphere is called sublimation. This happens
when water molecules leave the frozen (solid) state and directly enter the atmosphere without first
changing into a liquid. This process requires more heat energy than the evaporation process. You may
have witnessed the sublimation process during the wintertime when snow on the ground disappears
without having melted. Sublimation also describes the formation of frost. That is, water vapor doesn’t
condense first to a liquid before becoming frost; it goes directly from the vapor state to the frozen state.
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