Follow the quest to understand the laws of motion and gravity--to formulate the ups and downs of physics and solve the mysteries of the strange forces that propel all objects on Earth.

Whenever we throw a baseball, sail a boat, or guide a spacecraft through the atmosphere, we manipulate the principles of motion and gravity. But for centuries these fundamental laws of nature mystified mankind.

Author Glen Phelan guides young readers through the quest towards understanding the invisible forces at play on our planet. Ancient wisdom posited Earth as the center of the universe, but studies of the universe led Copernicus and Galileo to challenge that idea and radically alter perceptions of physics. Later, the Englishman Isaac Newton made the big breakthrough by defining the meaning of gravity (with the aid of a famous falling apple).

"An Invisible Force" traces the historical and scientific path to man's understanding of motion and gravity. From stargazing astronomers to a look at accelerating future developments, young readers are drawn into an age-old science quest.