Weather Stations: Phase Change
Adapted from "Make It Rain!," Windows to the Universe Original (now stored at http://www.windows2universe.org/), at the University Corporation for Atmospheric Research (UCAR), ©1995–1999, 2000.
Children observe the water cycle in action! Water vapor in a tumbler condenses on chilled aluminum foil — producing the liquid form of water familiar to us as rain and dew. They discuss how Jupiter's lack of a surface simplifies its water cycle and consider that ammonia and ammonia compounds play a role in its more complicated atmosphere.
What's the Point?
- Earth's atmosphere is a mixture of nitrogen, oxygen, and trace gases that include water vapor.
- Jupiter's atmosphere is different than Earth's. It contains ammonia but may only contain relatively little water.
- Water on Earth can be found in liquid, gas, or solid states as it goes through the water cycle. Water evaporates from Earth's surface in the form of water vapor, rises and cools as it moves to higher elevations, condenses as rain (liquid) or snow (solid), and falls to the surface where it collects in lakes, oceans, soil, and in rocks underground.
- The gases in Jupiter's atmosphere also undergo cycles of evaporation, condensation, and precipitation. This cycle is simplified on Jupiter since there is no surface with lakes, oceans, soil, or ground.
The following materials are for this Weather Stations activity.
Three sets are recommended for a station:
- 2 identical clear containers, (1 filled with ice, 1 filled with water)
- 1 clear plastic tumbler for holding hot water
- Small sheet of aluminum foil (enough to cover the top of the tumbler)
- Electric tea kettle or carafe of boiling hot water
- Ice cubes (enough to use 3–4 during each demonstration)
- 1 spoon
- 1 large bowl for periodically emptying tumblers
- Towel for drying and cleaning spills
- Hot pads
- The Earth's Water Cycle Poster (adapted from Introduction to Clouds)
For each child:
- His/her My Trip to Jupiter Journal or just the relevant "Weather Stations: Phase Change" pages
- 1 pencil or pen
- Shape the aluminum foil over the top of the tumbler so that it will hold three or four ice cubes and their melt water. Allow the foil to crinkle, but make sure it does not tear.
- Set up the station with access to an outlet if the tea kettle is to be used.
- Between each demonstration, empty the tumbler and wipe the aluminum foil.
- Arrange for an adult or older child to facilitate this station, as it requires handling of boiling hot water. Please use proper caution!
1. Use the containers of ice and water to prompt a discussion about state changes.
- Is a transformation from solid ice to liquid water, and back again, possible? Yes, of course it is, it happens all the time!
- What are the three states of water — or the three conditions in which water can be found? The solid — ice, the liquid — water, and the gas — water vapor.
- Are ice and water made of the same "stuff?" Yes. Ice and water (and water vapor) all have the same chemical composition — they are made of molecules of hydrogen and oxygen (H2O).
- What about water vapor — is it the same "stuff?" Yes.
- Where do we find examples of ice, water, and water vapor naturally on Earth? Ice falls as snow and is found in glaciers and ice sheets at the Earth's cold poles. Water is in the oceans and rivers and comes out of our water taps. Water vapor is an invisible gas in our atmosphere. Water vapor can condense in the atmosphere as clouds. When the water vapor in clouds cools, it can condense into a liquid and fall as rain or freeze into a solid and fall as snow or ice crystals. Earth is unique in that all three states of water exist on our planet's surface!
- What would it take to make the ice in the container change states from a solid to a liquid? Time and temperatures warmer than freezing.
- What would it take to make the water in the container change states from a liquid to a gas? The water will need to be heated (to boiling).
- If the container with the water was left out for several days, what would happen to the water? It would "go away" — evaporate. The liquid water would turn into a different state. It would become water vapor, a gas. Our atmosphere contains water vapor; clouds are formed by the condensation of water vapor.
2. Explain to the children that they will observe the state change from water vapor to liquid water — condensation — that creates rain on Earth — and Jupiter!
- a. Carefully add one cup of boiling hot water to the tumbler. Place three to four ice cubes in the aluminum foil with some of the cold melt water. Cover the mouth of the tumbler with the aluminum foil.
b. Ask for predictions and allow the children a few minutes to discuss their ideas and record them in their journals.
3. Within a few minutes, observe drops falling from the aluminum foil. Ask the children to describe what happened.
- How did the temperatures of the water and the aluminum foil compare? The boiled water was hot and the surface of the aluminum foil was cold.
- What states of water can you find in the tumbler? Liquid (hot water and "rain") and vapor (invisible gas).
- Where did the water come from that fell as "rain"?
Listen for "water vapor" or "water in the air" as the correct answer. If the children name the hot water as the source, point out that the hot water and aluminum foil are not touching; they are separated by air. Guide them to identify the vapor — the invisible form of water in the air — as the source.
- How did the crinkles on the aluminum foil help form the rain? The aluminum foil’s crinkles helped gather the water droplets up so that they grew heavy enough to fall.
Have them record the results in their journals.
4. Compare the model to Earth's and Jupiter's atmospheres.
- How do the temperatures of Earth's surface and lower atmosphere — up to about the level where clouds form and jet airplanes fly — compare? Especially if the children have visited the temperature and pressure station, they should suggest that the surface is relatively warm and the atmosphere at the level of clouds is cold. Gently correct any suggestions that the atmosphere is warmer because it is closer to the Sun. This region of Earth's atmosphere grows colder with altitude because temperature drops as the air pressure drops.
Explain that while Jupiter doesn't have a surface like Earth does, its deep atmosphere is warmer than the upper reaches of its cloud layer.
- What does this mean for water, ammonium hydrosulfide, and ammonia gases convecting up from Jupiter's lower layers? They will condense into clouds.
5. Show the poster of Earth's water cycle to the children.
- What portion of Earth's water cycle did we just model? Discuss the children's ideas, which may include evaporation, condensation, and precipitation.
6. Distinguish between Jupiter's rain and Earth's water cycle.
- Where does the water come from that makes clouds on Earth? Water vapor in the air; water vapor in the air, in turn, comes from the evaporation of water from oceans, rivers, soil, plants, and animals.
- Where does falling rain on Earth go? Into oceans, rivers, and soil.
- Does Jupiter have oceans, rivers, or soil? Probably not.
Add that scientists think that Jupiter has a layer of liquid hydrogen, but it does not have a solid surface with rivers and soil. Jupiter's rain evaporates back into vapor again when it falls to the deeper, warmer layers!
Summarize that Earth and Jupiter both have cycles of evaporation, condensation, and precipitation. Changes in temperature cause water — and in the case of Jupiter, other substances as well — to change phase and form vapor, clouds, and rain.
- How do meteorologists on Earth study the water cycle? They measure the amount of precipitation and use temperature, pressure, and wind data in computer models to predict storms.
Juno will map the atmosphere's temperature at different depths from its orbit and gather information about the trace components water and ammonia. Scientists have been surprised to detect very little water during previous missions to Jupiter, and Juno's instruments will provide a deeper look into Jupiter's atmosphere on a hunt for the missing water. Explain that the information that Juno collects will also be used in computer models to better understand Jupiter's atmosphere.
Allow the children time to note their conclusions in their journals.