Every human, plant, and animal depends on water for
survival. It's controlled by the sun, which produces
energy in the form of heat. This heat energy causes the
water in the world's oceans, lakes, and even puddles in
your backyard to warm and evaporate. When water is heated,
it changes from a liquid to a gas. This gas is called
water vapor, and the process is called evaporation. When
plants give off water vapor, it's called transpiration.
When water evaporates, it rises into the cooler air,
collects, and forms clouds. There, the water vapor
molecules cool down and change back into liquid water.
This is called condensation. As more and more water vapor
cools into the clouds, the water droplets that form the
clouds become larger and larger. These droplets get so big
that the swirling winds in the atmosphere can no longer
hold them up. The droplets fall from the sky.
Precipitation is the term for the falling, condensed water
molecules, which come down as rain, snow, sleet, or
hail--depending on conditions in the atmosphere.
Place the small container in the middle of the large,
clear bowl. Fill the bowl with a little water, being
careful not to fill the small container inside. Cover the
bowl with plastic wrap, and fasten the plastic wrap around
the rim of the bowl with your rubber band or string. Put a
weight on top of the plastic wrap in the center. (See
Picture below.) Now put your contraption on a windowsill
or somewhere that the sun will hit it.
How long does it take for water to evaporate and condense
on the plastic wrap? Where does the water go after it
condenses on the plastic wrap?
And Analyze Data:
The heat of the sun
evaporated the water, which raised, condensed on the cool
plastic, and fell into the small container. This is a
small-scale replica of the water cycle that occurs every
day on earth.