Cloud-Breathing Paper CupWENXUAN ZHANGAward: Top 100
School: georgia school ningbo This picture shows a paper cup producing white fog when warm water is poured into it. The cup contains small pieces of dry ice (solid carbon dioxide). When warm water is poured into the cup, the dry ice warms up and changes dry ice directly from a solid to a gas. This process is called sublimation. Sublimation absorbs a lot of heat, so the air right around the cup becomes very cold. At the same time, the warm water evaporates, making invisible water vapor in the air. When this warm water vapor meets the cold air near the cup, it cools down and turns into tiny liquid water droplets. This change is called condensation (liquefaction). These tiny droplets float in the air and scatter light, forming the thick white fog that flows out of the cup. The fog is not smoke or carbon dioxide gas -- it is made of small water droplets of water. 
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