- Galileo discovered that all objects accelerate at the same rate when falling, due to gravity, regardless of their mass. Heavier objects experience a greater force of gravity but require more force to accelerate as their mass increases. - Newton's Second Law states that acceleration depends on both the mass of an object and the net force acting upon it. Greater mass requires a greater force for the same acceleration. - Newton's Third Law states that for every action there is an equal and opposite reaction. Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force back on the first.