Some good science fair projects include taco sauce cleaner and color-changing milk. Another experiment, called walking on eggshells, involves stepping on a carton of a dozen eggs to find that the eggs do not crack with the weight of a person standing on them.
To test the taco sauce cleaner experiment, have dirty pennies, taco sauce, vinegar, tomato paste, salt, water, small plates and masking tape ready. To do the experiment, place two or three equally tarnished pennies on each of five plates. Mark each plate with masking tape to indicate which ingredient is being tested. Cover the pennies with the various ingredients -- vinegar, tomato paste, taco sauce, salt and water -- and let them sit for at least two minutes. Rinse the ingredients. Notice that none of the ingredients did a good job cleaning the penny. Next, try using a mixture of the ingredients on each of three plates. On the first plate, use tomato paste and vinegar, on the second, use salt and vinegar, and on the third, use tomato paste and salt. Cover the pennies on each plate with the mixtures, and give at least two minutes to react. Rinse the pennies under water to find that vinegar and salt was the most successful cleaner.
For color changing milk, pour enough whole or 2-percent milk onto a dinner plate to cover the bottom. Add four different colors of food coloring to the milk, keeping the drops close to the center of the plate. Use a clean cotton tip to touch the center of the milk. Next, place a drop of liquid dish soap on the other end of the cotton swab, and place the tip in the middle of the milk for 10 to 15 seconds. Notice how the colors in the milk shift and move.