Roseann Feldmann & Sally M. Walker 
Put Levers to the Test [PDF ebook] 

What do hammers, wheelbarrows, and brooms have in common? All of them are levers! Levers are simple machines. They help us to do jobs more easily. But don’t take our word for it. Put levers 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!