One project that is fun for elementary students to do is the ice-cube project. Students should form an hypotheses as to whether they think hot water or cold water will freeze the fastest. All you need are some ice trays and a digital food thermometer. Fill one plastic ice tray with hot water and one with cold water Check and record the temperature in each tray and place them both in the freezer. Take the trays out and check the temperature every 30 minutes until one tray has formed completely frozen ice-cubes. Your students will have the answer.
You can use this project to show how some things just don't mix well. You will need an empty soda bottle, water, food coloring and two tbsp. of cooking oil. Add a few drops of food coloring to water and pour two tbsp. of the colored water into the empty soda bottle along with two tbsp. of cooking oil. Put the lid on tight and shake the bottle. Watch the bottle for a few minutes. It will seem as though the water and oil are mixing, but the oil will float back to the top after a few minutes. Explain to the students that while water can mix with other liquids to form solutions, oil and water will never mix because the water molecules are strongly attracted to each other and the oil molecules are likewise drawn together. The oil floats because it has a lower density than water.
This experiment allows kids to find out what happens when you look at tonic water under a back light. You will need a black light, which can be found at most hardware stores, a bottle of tonic water, a highlighter and a dark room. Carefully break open the highlighter and remove the felt. Soak it in a small amount of water for a few minutes. Find a dark room, then turn the black light on near the water and watch how it glows. The ultra violet (UV) light coming from the black light lamp makes things called phosphors become active. Tonic water and the dye from the highlighter contain phosphors that make the UV light--which we can't see--turn into visible light, which causes the water to glow.
Second grade students can have a fun time with this simple project that helps explain gravity. All you need is a full glass of water and a piece of cardboard. Take the piece of cardboard and place it over the top of the glass, making sure no air bubbles enter the glass as you hold onto the cardboard. Turn the glass upside down over a sink just to be on the safe side. Remove the hand holding the cardboard in place. The cardboard and water should both stay put, even though the water is upside down, appearing to defy gravity. Explain that with no air inside the glass, the air pressure from outside the glass is greater than the pressure of the water inside. The extra air pressure holds the cardboard in place and keeps the water where it should be.