Roseann Feldmann & Sally M. Walker 
Put Wheels and Axles to the Test [PDF ebook] 

What do bicycles, doorknobs, and screwdrivers have in common? All of them use wheels and axles to perform work! Wheels and axles are simple machines. They help us to do jobs more easily. But don’t take our word for it. Put wheels and axles to the test with the fun experiments you’ll find in this book. As part of the Searchlight Books(TM) collection, this series sheds light on a key science question-How Do Simple Machines Work? Hands-on experiments, interesting photos, and useful diagrams will help you find the answer!