CK-12 Foundation
Ck 12: Physical Science: Compound Machine
[Free Registration/Login may be required to access all resource tools.] Provides a definition of a compound machine with examples and discusses the efficiency and mechanical advantage of compound machines.
Museum of Science
The Museum of Science: Gadget Anatomy
This site from The Museum of Science presents some compound machines and asks students to identify which simple machines they are composed of. Students provide their answer and receive immediate feedback.