Add oil, water, food coloring and Alka-Seltzer to a water bottle and watch a simple science experiment that is a lot of fun for kids (and adults).
What you need
Clear plastic bottle
What to do
Pour water in a clear water bottle (about quarter full), add vegetable oil until the bottle is nearly full. Add some food coloring. (Kids picked their favorite colors: red and yellow). Break Alka-Seltzer pills into smaller pieces and drop one in. Watch the show! When the bubbling stops, add another piece of Alka-Seltzer.
What to tell kids
Oil floats to the top because it is lighter than water. Food coloring is the same density as water, so it sinks through oil to the bottom. As Alka-Seltzer dissolves it makes gas (carbon dioxide). Gas is lighter than water so it floats to the top. As it moves up it brings some colored water with it to the top. At the top air comes out of a colored water blob and it gets heavy again and sinks.