Book excerpt: Why was aluminum once more valuable than gold? Why are some buildings built on giant springs and where can they be found? Why does a nuclear waste remain hazardous for thousands of years? In this book, you will learn about the chemical and physical changes that can occur in materials, including chemical and metal reactions, the effect of substances on materials, and the various types of physical changes and their causes. Find out what a huge part the material world plays in your life! Each book in the 'Material World' series looks at a key area of materials science, covering subjects such as states of matter, material characteristics and behavior, the uses of different materials, and the technology used to make new materials or change existing ones for new purposes.