Many children question why the sky is blue, and many adults don't have a proper answer. Light is made up of a spectrum of colors, which we can see in a rainbow. But as light moves through the atmosphere and comes in contact with dust and molecules, most colors pass straight through, but the blue part of the spectrum bounces off and scatters, making it the color we see with our eyes. According to Science Made Simple, children can see all the colors in the spectrum by placing a pan of water in a sunny location. Place a mirror in the water angled toward the sun, and hold a piece of paper above the pan. Children should be able to see all the colors in the spectrum of light on the paper.
Many children understand clouds and their relationship to rain, but they will be even more interested in a cloud they can create themselves. Use a 2 liter plastic empty soda bottle and fill the bottom with some warm water. Close the bottle with a rubber stopper attached to tubing and a foot pump. Pump as much air in as possible and when the stopper is removed a small cloud will form. Instead of water, use a teaspoon of rubbing alcohol in the bottle, and witness a much more impressive cloud. Be sure to wear safety glasses as you witness the water molecules being placed under pressure. When the stopper is removed the molecules expand, the air cools and the molecules condense to form a cloud.
Air pressure has a large effect on our weather and our bodies. Using a peeled, hard-boiled egg and a glass bottle, children can see the strength of air. Make sure the egg fits on top of the bottle opening but will not fall through. Have an adult light a match and drop it into the bottom of the bottle. Immediately place the egg on top. As the flame burns up the oxygen in the bottle, the air pressure becomes lower in the bottle than the air outside the bottle. According to "Egg in a Bottle" by Science Fair Adventure, the egg will get pushed into the bottle due to the higher air pressure pushing on it.
With adult help, students can use a clean soda can for this experiment in air pressure. Place about a tablespoon of water in the bottom of a soda can and heat it on the stove. Once water vapor starts coming out the top continue heating for another minute. Grab the bottom of the can with tongs and place it quickly upside down into a bowl of cold water. According to Steve Spangler Science, the water vapor in the can quickly cools and condenses, which takes up less room than the water vapor did, and as a result the walls of the can get sucked in with the change in temperature and pressure.