Kids love the sudden foaming action that occurs when vinegar, a mild acid, hits baking soda, also called bicarbonate of soda. To demonstrate for a class, put baking soda in the bottom of a large, clear glass bowl. You can use vinegar straight from the bottle or add a bit of food coloring to create an even more dramatic effect. Use small clear plastic cups if students do the experiment on their own. A heaping tbsp. of baking soda with about 1/4 cup baking soda is enough for each student.
The fun of oobleck is that it changes right in your hands. Mix two cups of corn starch with one cup of water in a plastic bowl. Stir until all the corn starch is wet. The mixture seems like a powdery solid at first but then pours like a liquid. You can add food coloring if you wish although be aware that it can stain kids' the skin if they play with the oobleck -- and how can they resist?
Cut a potato in half and put the halves flat side down on a plate. Take two 1-foot lengths of insulated copper wire and strip about 2 inches of insulation from each end. Wrap the end of one wire around a galvanized nail, then press the nail into one potato half. Wrap the end of the second wire around a penny and press the penny into the same potato half, making sure it is not touching the nail.
Take a third length of wire with the ends stripped. Wrap one end around a second penny and insert the penny in the other potato half. Insert a second nail in the potato. It should not have wire wrapped around it and it should not touch the second penny. Connect the wire from the penny in the first potato to the nail in the second potato. Touch the free ends of the wires to a bell or light mounted with attachments for wires.
Collect six or eight clean, empty glass jars that are all the same size. Add about an inch of water to the first jar. Increase the amount of water in each successive jar. Food coloring makes the water levels easier to see. Instruct students to tap the jars gently using a pencil or metal spoon. Encourage students to make up tunes with the different notes they are able to play.