Do you like rainy days? Have you ever wondered how rainfall forms? In this experiment, we will explore the source of raindrops and where they will end up, which can all be explained by the water cycle!
Materials:
A gallon-size Ziploc bag
Sharpie marker
Blue food coloring (optional)
Hairdryer
Time Estimated:
15 minutes
Directions:
First, to create our model of the water cycle, draw a sun at the top right of the Ziploc bag, then hills at the bottom left of the bag with an ocean next to it. Mark “collection” under the ocean. Then, draw arrows pointing from the ocean to the sun and label the arrows with “evaporation.” Next, draw a few clouds and raindrops on the bag's top left and write “condensation” in the clouds and “precipitation” among the raindrops. Finally, trace the path from the hills to the ocean and label it as “runoff.”
It is now time to fill the bag up with “ocean!” Fill the bag about ⅓ of the way up with water and add a few drops of food coloring to the water.
You can choose to place the bag next to a sunny window and observe the water cycle at different times throughout the day or speed things up by using a hairdryer to heat up the bag. If you do want to use a hairdryer, use it in the low-heat mode so that it can heat up without melting the bag.
When you see drops of water appearing along the sides of the bag, you are observing the water cycle!
Think Like a Scientist!
How does heat transform water into vapor?
What factors can affect the rate of evaporation, or the rate at which water turns into vapor?
How Does It Work?
The water cycle starts with evaporation when the sun heats up large bodies of water and transforms water from the liquid state at the surface of Earth into a gaseous state of vapor rising into the atmosphere. This transformation occurs as heat forces the bonds that hold water molecules together to break apart; as can be imagined, increasing heat stimulates the rate of evaporation. Other factors that can affect evaporation include humidity, wind speed, and solar radiation. The major source of evaporation comes from the ocean, but it can also occur in soils, snow, and ice.
The next step in the process is condensation which occurs when warm air rises in the atmosphere and encounters a cool surface, which leads to the loss of its capacity to hold water vapor. As a result, water vapor transforms back into the liquid state, and excess water vapor condenses around tiny dust or smoke particles to form clouds. In other words, clouds are simply masses of water droplets in the atmosphere. When saturated clouds cannot hold any more water vapor, the density of the vapor molecules increases. The vapor then condenses and becomes rain, snow, or hail. Some of the precipitation might percolate into the soil and become part of the underground water, while the remainder flows directly as surface runoff and gets recollected into large bodies of water.
Further Exploration:
The water cycle plays an essential role in distributing water all over the world and feeding fresh water to all life forms. Evaporation helps to purify water, as it allows pollutants and sediments in water to be left behind by water vapor. On the other hand, condensation and precipitation stages also help to explain different levels of humidity in cold and warm regions. Because cold air holds less water vapor than warm air, water vapor condenses more easily in cold climates, so it is more likely to rain in cold climates! In contrast, warm regions tend to be more humid because water vapor remains in the air instead of condensing into the rain.
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