We've all heard of gravity. It's what causes objects to fall, right? Well that's the everyday notion but we'll look at gravity from a more scientific approach. A gravitational force exists between all objects. Any two objects that you can think of are attracted to one another. How strong that attraction is, however, depends on two important quantities. They are the mass of the objects and the distance between them.
Johannes Kepler believed that the sun exerted a force on the planets. He studied and analyzed data for several years to develop three laws to describe the motion of every planet as they revolve around the sun.