Cloud Maker: How Does a Cloud Form?
How Does a Cloud Form?
- Rubber glove (type used when washing dishes)
- Quart (liter) glass jar
- Tap water
- Match—to be handled only by an adult
- Two wide, medium-sized rubber bands
- Desk lamp
- Sheet of black construction paper
- Adult helper
- Cut a 5-inch (12.5-cm) square from the top of the glove.
- Rinse the inside of the jar with water.
- Pour most of the water out of the jar, leaving only enough to cover the bottom of the jar.
- Ask an adult to light the match and allow it to burn for about three seconds. Then blowout the match and have your adult helper hold the smoking end inside the jar for two seconds.
- Immediately stretch the rubber square over the mouth of the jar and ask your helper to place the rubber bands over the rubber square and around the neck of the jar. The rubber bands must be tight enough to hold the rubber square in place.
- Turn the jar on its side and rotate it so that the water washes over the inside walls of the jar.
- Hold the jar in front of the lamp so that the lamp illuminates the jar from behind and does not shine directly in your eyes.
- Ask your helper to hold the sheet of black construction paper about 12 inches (30 cm) behind the lamp.
- With your fingers push the center of the rubber square down into the jar about 1 inch (2.5 cm).
- Observe the contents of the jar.
- Pull the center of the rubber square upward about 1 inch (2.5 cm).
- Observe the jar's contents with the rubber square stretched upward, and continue to observe as you release the rubber square.
The contents of the jar look clear when the rubber square is pushed down. Pulling the rubber sheet upward causes the inside of the jar to become cloudy, but this cloudiness disappears when the rubber square is released.
When a liquid molecule acquires enough heat energy, it breaks away from the attraction of other molecules in the liquid and escapes as vapor into the space above the liquid. This process of changing a liquid into a vapor is called evaporation. Evaporation occurs faster if the surrounding temperature increases suddenly. Condensation (changing vapor into a liquid) is the reverse of this process, and it occurs faster when the surrounding temperature decreases suddenly.
In this experiment, when the rubber square is pushed into the jar, the increase in pressure causes an increase in temperature, thus more molecules of invisible water vapor are formed. When the rubber square is stretched upward, the contents of the jar expand, reducing the pressure inside the jar. The reduction in pressure causes a decrease in the temperature inside the jar, which in turn causes the water vapor to change back to water (a liquid).
These changes occur rapidly. When the rubber square is stretched upward, water molecules condense and cling to the smoke particles suspended in the air inside the jar, forming water droplets. These droplets are large enough to scatter the light, thus a cloud (a visible mass of water particles that float in the air, usually high above the earth) appears in the jar. The cloud scatters in various directions when the rubber square is released and the liquid water molecules evaporate. The tiny smoke particles are too small to scatter the light, so the jar appears clear.