You've probably noticed that when water gets really cold, it freezes. And you've probably seen steam coming from a pot of boiling water. But do you know why that happens? Do you know how wood burns or what's inside a fire extinguisher? When scientists have questions like these, they conduct experiments to find the answers. Through countless experiments, scientists have learned about different states of matter--solids, liquids, and gases--and what makes matter change from one state to another. Explore the fascinating discoveries scientists have made about the matter we use every day.