Fact 1: Gravity causes objects that have mass to be pulled down on a planet.

Fact 2: Gravity was defined by Newton.

Given the two facts above, answer the question "The thing that causes objects to be pulled down on a planet was defined by which scientist?" with the following options: 
- friction
 - Darwin
 - kinetic
 - the sun
 - Galileo
 - Kepler
 - energy
 - Newton


 

        Newton 