Clouds are concentrations of water vapor in the sky. They form when water evaporates (turns to water vapor) from oceans and freshwater sources, such as ponds and lakes. As the water vapor swirls around, it condenses (changes to a liquid) and forms small droplets, which in turn, bump into each other and join to form larger droplets. This results in precipitation, especially if the vapor cloud encounters a mass of cold air. Water falls to earth as liquid droplets or ice crystals–rain, sleet, hail, or snow–depending upon the air conditions. A typical raindrop is 0.1 mm in diameter, although it could easily be larger or smaller.
Cirrus clouds are high, white, and wispy. Stratus clouds are gray and hover close to the ground in layers. Cirrus and stratus clouds often bring light precipitation and fog. (At altitudes over 15 m, fog is considered to be a cloud.) Cumulus clouds look like white tufts of cotton candy and usually accompany fair weather. Cumulonimbus clouds are huge black clouds that often lead to lightning, thunder, and heavy rain. Nimbus clouds are low, dark clouds that lead to rain or snow.
The conditions that lead to cloud formation are easy to reproduce on a small scale. You can condense water vapor into liquid droplets to model what happens in the sky overhead. This activity has two parts: making little clouds, and condensing them into miniature rainstorms.
- Beaker (or heat-resistant Pyrex or Kimax cup)
- Stove or hot plate (requires adult help)
- Tongs or thick oven mitt
- Metric measuring spoons
- Erlenmeyer flask (A narrow-mouthed bottle will do.)
- Clamp and support (optional)
- Metal pan (such as a pie tin or cake pan)
- Metric ruler
- Notebook and pencil
To Make Clouds
- Have an adult help you heat water in a half-filled beaker until it boils, and set it to the side using tongs or a thick oven mitt. Let the water cool for 30 seconds to 1 minute.
- Use the tongs to pour a small amount of the hot water 20 to 30 mL–into a flask.
- Place an ice cube so that it rests on the mouth of the flask. (If necessary, fuse a couple of cubes by squeezing them together, to prevent them from falling into the flask).
- Observe what happens inside the flask.
- As an extension, vary the initial temperature of the water, or the amount of ice, to compare the rate and quality of cloud formation.
To Make Rain
- Adjust the amount of water in the beaker so that it is half full. Set the beaker on a hot plate.
- Using a clamp, mount a metal pan to a support 10 to 20 cm above the beaker, at a slight angle. Put enough ice cubes in the pan to cover the bottom. (If you do not have the equipment to clamp the pan in place, you can ask an adult to hold the pan by the edge using an oven mitt. Make sure the person keeps his or her hand away from the steam.)
- Have an adult bring the water in the beaker to a boil.
- Observe what happens on the bottom of the metal pan. Collect the "precipitation" that drips off the pan in a cup.
- You may also want to measure and record variables such as the length of time the water boils, the volume of the water that boils off, and the volume of precipitation that falls.
Clouds: From Mare's Tails to Thunderheads (First Book series) by Suzanne Harper (Danbury, Conn.: Franklin Watts, 1997).
Janice VanCleave's Weather: Mind-Boggling Experiments You Can Turn into Science Fair Projects (Spectacular Science Projects series) by Janice VanCleave (New York: John Wiley & Sons, 1995).
Science Projects about Weather (Science Projects series) by Robert Gardner and David Webster (Berkeley Heights, N.J.: Enslow, 1994).
Simple Weather Experiments with Everyday Materials by Muriel Mandell (New York: Sterling, 1991).
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.