Both Kepler's and Galileo's experiments and calculations involved objects moving faster the closer they were to other objects. Newton was the one to explain why.

Newton told the story of how he was sitting in his mother's garden when suddenly he was disturbed by the sound of a falling apple in a nearby tree. It was at that moment he had the idea of a universal force. The force that was pulling the apple could be the same force that was holding the moon in orbit!

Newton knew Kepler's laws and so he suggested that the rate at which an object falls depends on the strength of the GRAVITATIONAL FORCE acting on it.

The further you are away from the Earth - the weaker the force of gravity pulling you back.

He worked out that the size of the force acting on the two objects changes according to the INVERSE-SQUARE LAW.

What Newton discovered was that everything has gravity! The law of Universal Gravitation.