Professor Williams wrote some statements on the board: 1. Newton observed an apple falling off a tree and speculated that all things on Earth are subject to the force of gravity. 2. He repeatedly test

Professor Williams wrote some statements on the board: 1. Newton observed an apple falling off a tree and speculated that all things on Earth are subject to the force of gravity. 2. He repeatedly tested his idea. 3. He found that any two objects in the universe have a gravitational attraction to each other. 4. His findings cannot be edited or replaced. Professor Williams is discussing