Make your favorite cake recipe four times: once without baking powder, once without eggs, once without oil, and once with all of the correct ingredients. Label each cake pan. While the cakes bake, explain that heat causes chemical reactions in the batter that turn it into cake. Explain that heat causes baking powder to bubble, making the cake light and fluffy. Heat causes the protein in the eggs to change, making the cake firm. And oil keeps the heat from drying out the cake. Once cakes are cooked and cooled, test them to verify these statements.
Plant pumpkin seeds in potting soil in plastic cups or small pots. Watch as they grow, and record the changes in a journal. When the seedlings are large enough, transfer them to an outdoor location and continue to monitor and record their progress. As an additional experiment to show how plants use water, place several stalks of celery with their leaves attached in a glass of water. Have your child add a few drops of food coloring to the water. After a day or two, the celery leaves turn the color of the food coloring.
Place a 16-ounce plastic soda bottle inside an aluminum cake pan. Using a funnel, have your child pour in 20 ml. peroxide (6 percent solution), 10 ml. dish washing liquid, and one packet of yeast. After one or two minutes, foam from the oxygen produced by the mixture will spray out the top of the bottle. Explain to your child that the mixture of peroxide, soap, and yeast produces an exothermic reaction, or one that creates heat. Encourage your child to play in the foam, which feels warm. You may want to wear safety goggles for this experiment.
Kids are usually fascinated by quicksand when they see it on television or in movies. To simulate quicksand, mix 1 1/4 cups cornstarch with 1 cup water until is has the consistency of honey. Have kids move their hands through the mixture slowly. Then, have them move their hands quickly. They will notice a difference. Explain that the cornstarch and water mixture, as well as quicksand, are non-Newtonian liquids, meaning their viscosity, or resistance to force, changes depending on the force applied. Explain that the viscosity of most liquids--like water and milk, for example--changes only with temperature.