Galileo didn't actually use inclined planes to directly conclude that an object in motion stays in motion unless acted upon by a force. That concept is known as Newton's First Law of Motion, which came much later.

However, Galileo's experiments with inclined planes were crucial in laying the groundwork for this understanding. Here's how:

Galileo's Experiments:

1. Observing Rolling Balls: Galileo observed that balls rolling down an incline would accelerate, and then continue rolling up another incline, almost reaching the same height they started at.

2. Reducing Friction: He realized that the reason the ball didn't reach the same height was due to friction. By reducing friction (using smoother surfaces and rolling objects), he observed that the ball came closer to the original height.

3. Extrapolating to a Horizontal Surface: He reasoned that if there were no friction, the ball would continue rolling forever on a horizontal surface. This led him to the concept of inertia, the tendency of an object to resist changes in its motion.

Connection to Newton's First Law:

Although Galileo didn't explicitly state Newton's First Law, his observations and reasoning directly contributed to its development.

* Inertia: Galileo's experiments demonstrated that objects in motion tend to stay in motion, which is the fundamental principle of inertia.

* Force as a Cause of Change: He recognized that friction was the force acting on the rolling ball, causing it to slow down. This foreshadowed the idea that forces are needed to change an object's motion.

In summary: Galileo's inclined plane experiments were not designed to prove Newton's First Law directly, but they provided crucial evidence and reasoning that led to its formulation. He showed that objects in motion tend to stay in motion, and that forces are needed to change their state of motion. This laid the foundation for Newton's groundbreaking work on motion and its causes.