Be sure that the pupils note how the water droplets collect, get larger, and eventually drip off the edge of the tray because of their increasing weight. We still have much to learn about rain formation. You may wish to repeat this activity using one tray with ice, and another empty tray.
Fog occurs when moisture is cooled and condenses in the atmosphere near the surface of the earth.
Now set the bottle on a tray of ice cubes and discuss what occurs inside. Fill the can about halfway with water that has been allowed to stand until it is at room temperature. Acid several ice cubes to cool the water. After a few minutes, you will observe droplets of water forming on the outside of the can. Explain that the formation is called dew.