How did Galileo’s work on free fall contribute to Newton’s laws of motion?

Galileo Galilei’s work on free fall and motion was foundational to the development of Isaac Newton’s laws of motion, as it helped replace the outdated Aristotelian worldview with a new, mathematized physics.123

Galileo’s specific contributions included:

• The Principle of Inertia: By experimenting with balls on inclined planes, Galileo deduced that objects in motion tend to remain in motion unless acted upon by an external force, such as friction. This discovery became the basis for Newton’s first law.42
• Understanding Acceleration: Galileo discovered that falling bodies undergo constant acceleration and that the distance traveled varies with the square of the time. This work on free fall provided a crucial empirical basis for understanding how forces change an object's motion.13
• Unifying Motion: Galileo’s insights allowed him to argue that terrestrial objects share the motion of the Earth, helping to resolve objections to a heliocentric universe. Newton later synthesized these ideas, demonstrating that the same force causing objects to fall on Earth also governs the orbits of celestial bodies.43

Ultimately, Newton integrated these findings into his Principia, creating a unified system of mechanics that explained both terrestrial and celestial phenomena.23