|
A "closed system" consists of a container that allows energy,
but not matter, to pass back and forth across the walls of the container.
The Earth's atmosphere, oceans, and land surface act as an almost closed
system. Water moves along a variety of pathways in this closed system.
This system of movement is called the "water cycle."
There is one main loop in the water cycle. Water evaporates at the ocean
surface and then moves as water vapor to the continents. The water vapor
condenses and falls as precipitation onto the continents. The water then
runs back into the ocean in streams and rivers. Of course, there is rainfall
onto the oceans, and there is evaporation of water from the continents.
There really is a cycle, however, because there is an excess of evaporation
over precipitation on the oceans, and there is an excess of precipitation
over evaporation on the continents.
Back To Top
|
