Wheels (Useful Machines)

How do wheels work? Why are doorknobs shaped like wheels? Why do buses have big steering wheels? For the answers to these and many other questions, read Wheels. Find out why cars have rubber tires. Learn about a kind of wheel called a gear. Discover how wheels can be used to measure lengths. This book describes what wheels are and how they work, different types of wheels and their uses, and other facts about wheels.