The Water Cycle

​ (a)   is a vital resource for all life on Earth. It moves in a continuously repeating flow from the ​ (b)   to the atmosphere and back again in the water cycle (also known as the hydrologic cycle).

• Earth
• Water

Liquid water changes to a gas state, known as (a)   , and moves to the atmosphere through two main methods. During (b)   , liquid water on the Earth is heated by the sun into the vapor. In (c)   , water within plant leaves exits as water vapor into the air.

• water vapor
• evaporation
• transpiration

The water vapor ​ (a)   into the upper atmosphere where it ​ (b)   and condenses from a gas to a liquid. It may even freeze into a solid. As these droplets stick together, ​ (c)   form.

• rises
• cools
• clouds
• warms

The droplets from clouds continue to stick together, and eventually, the droplets are too ​ (a)   to remain in the cloud. They fall back to the Earth's surface as a form of precipitation – rain, snow, sleet, or hail.

• heavy
• light

• The falling precipitation can land directly into bodies of water or onto land, where surface runoff takes it into the bodies of water. It can also percolate into the ground to become part of the groundwater supply.

• Precipitation can land in water bodies, cause surface runoff, or percolate into the ground.
• Surface runoff is the only way water reaches bodies of water.
• Precipitation only evaporates into the atmosphere.
• Groundwater is formed solely from underground rivers.

Percolate means

• To evaporate a liquid completely.
• To create a solid from a liquid.
• To filter or seep through a substance.
• To mix two substances together.

You studied this picture?

• no way

• Yes

• no

One common misconception is that the hydrologic cycle only includes evaporation, condensation, and precipitation. This neglects to include the role that ​ (a)   , runoff, and percolation have in the cycle.

• transpiration
• sleeping

The two forces that power the water cycle are

• solar energy and gravity
• earth's rotation and humidity
• ocean currents and pressure
• wind and temperature

​ (a)   provides enough heat to cause evaporation and transpiration. Once that water vapor cools in the atmosphere, it loses energy and condenses, and ​ (b)   provides the force needed for the precipitation to fall back to Earth. Gravity also drives water downstream and water percolation.

• Solar energy
• gravity