Earth science

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Video

Materials

• 1 large glass jar
• 1 plate
• 1 ice cube tray
• Food coloring (optional)
• 1 spoon
• Cooktop and pot (or other way to heat water)
• 1 matchbox
• Gloves
• Water

Short explanation

In the jar, the hot water evaporates and becomes water vapor. When the water vapor is cooled by the ice, it transforms to small water droplets that are visible as a cloud. The water vapor condenses more easily on the small particles that were released from the burning match.

Long explanation

When you pour water into the jar, some of the water will transform from a liquid state to a gaseous state (evaporate) and become invisible water vapor in the bottle. A liquid always changes to a gas to some extent, and vice versa, even if no change in temperature occurs. However, this so-called chemical equilibrium shifts in some direction when a temperature change occurs. In hot water, as in this case, a larger proportion changes to a gaseous state than in cold water.

There are now two things in the bottle's "atmosphere"; water vapor and the gas mixture called air. Water vapor, i.e. water in a gaseous state, is a natural part of the atmosphere and is sometimes considered a part of air.

The water vapor rises together with the heated air just above the water surface. Further up above the water surface, however, the air and water vapor are cooled down by the ice. What happens then is that the water condenses, i.e. is converted from a gas to a liquid. The tiny water droplets that form hang in the air and are visible as a cloud.

The role of the match in this demonstraton is to form small "pollutants" in the air, which increase the condensation of water. Water condenses more easily on small particles, such as dust grains or pollen.

If you're lucky, you will also see rain. This occurs when the small water droplets in the cloud become so numerous that they merge. Earth's gravity has a larger pull on these heavier water drops and they fall down.

The cloud formed in the bottle has formed in the same way as the clouds in the atmosphere. In nature, water constantly evaporates from Earth's surface by the Sun warming it. This water ends up as invisible water vapor in the air just above the ground. This air is heated by Earth's surface, which causes it to rise and take the water vapor higher up into the atmosphere. Up there, it cools and the water vapor transforms into liquid water again (it condenses). This preferably occurs on small particles in the atmosphere, such as pollen or pollutants. Now small water droplets are formed high up in the atmosphere (some water droplets also freeze into small ice crystals), and they form the clouds . These water droplets are so light that they don't fall down, but stay up there. When they become numerous enough, however, they merge into larger drops and turn into rain - or snow if it's cold.

The reason why you first fill the whole jar with water is to heat the glass. You want the condensation of water to take place in the "atmosphere", not on the cold glass.

The food coloring is for making it easier to see the water through the jar.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What happens if you have a larger jar?
• What happens if you have more or less water in the jar?
• What happens if you have cold water in the jar?
• What happens if you use fewer or more matches?
• How long can you make this "water cycle" last?

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