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

What do a doorstop, a butter knife, and the front of a boat have in common? All of them are wedges! Wedges are simple machines. They help us to do jobs more easily. But don’t take our word for it. Put wedges 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!