Weather: Fill the cup with water. Put shaving cream on top for a cloud. Explain that when clouds get really heavy with water, it rains! Then put blue food coloring on top of the cloud, and watch it rain.
Great activity during a weather unit. 2 liter soda bottle cut in half. Put about an inch and a half of warm water (w blue food coloring) in the bottom. Invert the top of the bottle with the lid on and fill with ice. Watch the water condensate and watch it "rain"