The Water Cycle
Introduction
The water cycle, also called the
hydrologic cycle, is a very integral part of our natural environment. It is how our world recycles the freshwater
living things need (ThinkQuest, 2002).
Since our planet is primarily covered in salt water due to the oceans,
seas, and salt water lakes (ninety-seven percent of the water), we need a
constant supply of freshwater cycling through for the nourishment of animals
and plants (Baptiste, 2000). When water evaporates into the air from the ocean,
it no longer contains salt so it becomes a new supply of freshwater (
The water cycle has several stages. Water evaporates from the ocean, lakes,
rivers, and streams. Evaporation is when
water is heated by the sun and the surface molecules become full of
energy. The water transforms into water
vapor and ascends high into the atmosphere (Baptiste, 2000). Plants also contribute water vapor. This process is called transpiration. Plants can transpire five to ten times as it
can hold in a day (The Green Lane, 2002).
The water vapor reaches a height in the atmosphere where it is no longer
warm and the vapor condenses into water again (Kimball, 2001). Condensation is the process of water vapor
returning to liquid water form. When the
water droplets are high in the atmosphere, they collect together to form
clouds. The clouds are moved by the wind
and when the clouds get extremely saturated, they finally begin to precipitate
(BrainPOP, 2002). Precipitation is when
a form of water such as hail, snow, rain, or sleet falls to the ground. The precipitation that falls then has
different options for where it will go.
Most of the precipitation actually goes immediately back into the ocean
(ThinkQuest, 2002). Another option is it can be absorbed into the ground where
it can be nourishing to plants (Wheeling Jesuit University/Center for
Educational Technologies, 2001). When it
is absorbed into the ground, it can become groundwater which is water that
seeps into the cracks between the tiny spaces in soil or small rocks. The water finally hits a point in the ground
where it cannot seep any further because there are no cracks big enough to fit
anymore. The water then begins to fill
in more of the soil above this point. At
the top of the water-filled spaces is the water table. When a water table is above the land surface,
then a lake or river is formed (Baptiste, 2000). Water that does not seep into the ground,
runs downhill into rivers and streams and is called runoff. The runoff
eventually returns to the ocean. Other
precipitated water evaporates again into the air (Marshall, 1994).
Students should be able to define all the
important vocabulary of the water cycle: evaporation, transpiration,
condensation, precipitation, runoff, and groundwater and put it in the correct
order within the cycle. They should
also be able to explain that the nature of a cycle is continuous. Just because our area is not getting rain
(perhaps a drought), does not mean that the cycle is stopped but that the wind
has blown the clouds other places to precipitate. Another important concept for them to explain
is that the driving force behind the water cycle is the heat from the sun. The heat, or the lack of heat, is what makes
the water change states of matter. They
need to know that clouds are made of water droplets or ice crystals because
this is often a misconception. They
might think clouds are made of cotton or some other substance. The students should also gain some
understanding that polluting our earth can cause the precipitated water to
become polluted by the waste in the air mixing with the moisture as well
(Baptiste, 2000).
The water cycle allows our world to
exist by constantly replenishing the plants and animals with fresh water. Students should understand the cycle because
it effects our world so entirely. They
see all the stages on a daily basis; surrounding us are water sources, clouds,
and rain (or snow or sleet). Since the
water cycle is so important, the students will research the topic as if they were
scientists. Once they gain the
vocabulary, concepts, and skills of the unit they will be performing
representations of the water cycle to first graders as if they were the
teachers. Because their authentic roles
take on the research and teaching of the water cycle, the students will have
ownership of what they have learned.
References
Baptiste,
P., Daniel, L., Hackett, J., Moyer, R., Stryker, P., & Vasquez, J. (2000).
Science. Farmington, NY: McGraw-Hill School Division.
BrainPOP
LLC. (2002). BrainPOP movies: Water
cycle. Retrieved November 5, 2002 from http://www.brainpop.com/science/ecology/watercycle.
Kimball,
J. (2001). The many adventures of drippy the
raindrop. Retrieved November 5, 2002 from http://www.kimballmedia.com/Drippy/ToMountainsAndBack/Entry.htm.
Marshall,
R. H., & Rosskopf, A. (1994).
Earth science. Circle Pines, MN: American
Guidance Service, Inc.
The
Green Lane. (2002). The hydrologic cycle. Retrieved November 5, 2002 from http://www.ec.gc.ca/water/en/nature/grdwtr/e_cycle.htm
ThinkQuest,
Inc. (2002). Water, water, everywhere. Retrieved November 5, 2002 from http://library.thinkquest.org/C0115522/article.php?qs_article_id=33&qs_language=EN&qs_section=NA
Wheeling
Jesuit University/Center for Educational Technologies. (2001). Earth
floor: Cycles. Retrieved November 5, 2002, from http://www.cotf.edu/ete/modules/msese/earthsysflr/water.html.