Kristi Holl 
Discovering the Nature of Gravity [PDF ebook] 

Gravity is now so universally accepted, it seems almost impossible to believe that for millennia, the force remained unknown. Yet it wasn’t until a few brilliant minds began asking the right questions that we could explain why we don’t float off the ground, why planets remain in orbit, and why time travel remains even a distant possibility. Interspersing history with science to support STEM learning, this exciting volume chronicles the evolution of our understanding of gravity by tracing the lives and experiments of the individuals instrumental in advancing gravitational physics.