Explore the ups and downs of gravity in this introduction to physical science by a trusted nonfiction team. What happens to a ball when it rolls off a table? It falls to the floor. Why doesn't the ball keep rolling straight ahead or fly up off the table? The answer is gravity. From density to inertia to free fall, David A. Adler skillfully explains how this invisible, but all too real force operates and what it means for our daily lives. Notable science experiments by Sir Isaac Newton and astronaut David R. Scott are covered. Also included are activities for kids to test at home and in the classroom. Anna Raff's bright and humorous artwork helps breakdown the concepts in a kid-friendly way. A glossary concludes the work.