This experiment will show your students how air pressure affects the ability of the air to hold moisture. In this case, the air in the jug is in a closed system, while the air in the atmosphere is in an open system. However, the principal physical changes work the same way in both the experiment and the atmosphere. IMPORTANT: This experiment requires adult supervision. Please read the Safety precautions BEFORE attempting to perform this experiment.
Have you ever walked outside on a foggy day? Did you realize that was a cloud on the ground? Did you get wet?
If the air is saturated with water vapor, what do you think that mean?
Discuss how hot air causes water vapor to evaporate.