Use this student sheet to perform one of the many hands-on inquiries written by the Robert Gardner. This particular lesson is taken from Gardner's book titled Weather Science Fair Projects.
Question: How can you make a cloud?
Hypothesis: You can make a cloud by allowing water vapor to cool and condense on small particles in the air.
1. You can make a cloud quite easily. Remove any labels from a clear, empty, two-liter plastic soda bottle. Pour about half a cup of warm water into the bottle. Screw on the cap and shake the bottle to saturate the air inside with water vapor.
2. Hold the bottle up against a light background, such as a window. Shake the bottle again. Then squeeze and release it. You will probably not see a cloud because one ingredient is missing—condensation nuclei (i.e., dust or particles).
3. Ask an adult to light a match, blow it out, and quickly lower the match into the mouth of the bottle so that smoke particles can form inside the bottle.
4. Put the cap back on and again shake the bottle, hold it up against a light background, and squeeze it to increase the pressure inside the bottle. Then quickly release your squeeze. This will decrease the pressure inside the bottle, allowing the water vapor to expand and cool. You should see a cloud form.
Results and Conclusions
A cloud is a huge mass of water droplets. As you have seen, warm air expands as it rises and cools. Because cold air cannot hold as much water vapor as warm air, some of the water vapor may condense on very small particles to form water droplets.
Most of the particles on which the vapor condenses come from the ocean. Breaking waves create bubbles that burst, sending tiny particles of salt into the atmosphere. The droplets that form around the salt particles are too light to fall in the strong air currents. But as the small drops bump into one another, they combine into larger drops and may eventually fall to the ground as raindrops. Each raindrop may be made from as many as one million tiny cloud droplets.
If the air in a cloud is very cold, the drops can freeze into small ice crystals, which grow bigger through collisions with smaller droplets. Falling through the bottom of the cloud, the ice crystals may melt into raindrops or fall as snowflakes. Whether they fall as rain or snow depends on the air temperature.
You may have accidentally made a cloud when you opened a can or bottle of cold soda on a hot day. The cloud probably appeared briefly just above the opening. When you opened the can, the gas pressure inside was released. The sudden drop in pressure allowed vapor to expand, cool, and condense.