Ramps and Wedges (Machines in Action)

Why do skiers use a zigzag path down steep slopes? How does a zipper work? How does a lock work? Ramp and wedges are simple machines that can be used to make other machines work. When you open a lock, cut something with scissors, zip up your coat, or use a doorstop you are using ramps or wedges. Ramps and Wedges explains what these machines are and how they help you do everyday things.