Making Clouds

When the baggie is in the jar, the pressure inside the jar is relatively high and the air relatively warm. Even though the humidity is high, there is no cloud.

When the baggie is pulled out the pressure drops, the air cools and water droplets condense to form a cloud.

This is such a classic experiment/demonstration that I think it has to be included in any weather unit. It is fun and it teaches a lot. I have done this in a variety of different ways but this site gives an easy description of how to do it using a plastic soda bottle.   The photos I’ve added show my son making a cloud using a glass jar, warm water, a sandwich baggie and a rubber band. Although the materials are slightly different the method is exactly like that described by the website. I like the jar because the glass is clearer and you can get a big pressure difference by pulling the baggie way out.

Whenever I do this activity, I first have students try to make a cloud without any smoke added.  They are usually pretty unsuccessful. Then we add the smoke and the clouds form, which makes the importance of condensation nuclei really clear.

This activity can work well with students at a variety of ages and levels.  With younger students I would just talk about pressure and temperature differences and how pulling the bag out mimics what happens to air as it rises and cools.  With older students you can go farther, talking about adiabatic cooling, saturation, dew point, etc.  There is a lot of learning connected to this little activity.

Depending on the age group you teach and on your school setting, you might not want each kid lighting a match to add smoke to their cloud chamber.  If your group is small you can go around and light a match for each individual or group. I have found that with a larger group it works well to use a stick of incense.  You can keep the incense burning and add a bit of smoke to each cloud chamber quickly and easily.