Gravity is one of the most important forces in the universe – invisible, but vital to our existence. It keeps our feet planted firmly on solid ground, and it keeps our planet from crashing into others. But how does it work? Readers will learn how gravity affects all matter, what effects changing gravity can have on human bodies, and how gravity interacts with other forces. They will also conduct gravity-related experiments to see this force in action. Features include eye-catching sidebars; experiments and activities to encourage hands-on learning; glossaries; charts, diagrams and more.