This is the fifth book in a five-book physical science series on simple machines. The books are designed for Spanish-speaking junior high school students. This volume explains the principles and some of the uses of inclined planes, as they appear in simple machines, by suggesting experiments and posing questions concerning drawings in the book which illustrate the principles. Answers to the questions are provided in the book; an evaluation exam i s also included. For other books in the series, see FL 002 897, FL 002 898, FL 002 899, and FL 002 900. (VM)