Here is an interesting experiment which is simple and easy to do in your kitchen, and yet is still quite impressive. Cut a potato in half. From one half, remove about a tea-spoon from the center, put some salt and toothpaste and mix it well. On the other half, make 2 holes and put 2 wires through. Close the potato with 2 toothpicks and let is act for 5 minutes. Then put some cotton on one end of the wires, and approach the other wire to the cotton. A spark will be generated that will put the cotton on fire!