landing?- If air pressure at sea level is one ton and at 5,500 m (18,000 feet) is one-half ton, what
is air pressure at 11,000 m (36,000 feet)?
Vocabulary
air pressure The force of air pressing on a given area.
altitude Distance above sea level.
climate The long-term average of weather.
condenses Changes state from a gas to a liquid; in the case of water, from water vapor to
liquid water.
evaporation The change in state of a substance from a liquid to a gas; in the case of water,
from liquid water to water vapor.
evapotranspiration Water loss by plants to the atmosphere.
greenhouse gases Gases that trap heat in the atmosphere; these include water vapor,
carbon dioxide, methane and ozone.
groundwater Fresh water found beneath the ground surface.
humidity The amount of water vapor held in the air; usually refers to relative humidity,
meaning the amount of water the air holds relative to the total amount it could hold.
noble gases Gases that usually do not react chemically and have no color, taste, or odor;
these are helium, neon, argon, xenon and krypton.
ozone A molecule made of three oxygen atoms; ozone in the lower atmosphere is a pol-
lutant, but in the upper atmosphere it filters out the sun’s most harmful ultraviolet
radiation.
photosynthesis The process in which plants produce simple sugars (food energy) from
solar energy; the process of photosynthesis changes carbon dioxide to oxygen.
precipitation Condensed moisture including rain, sleet, hail, snow, frost or dew.