What did Galileo observe by placing two inclined planes facing each other and rolling down a marble ball from top end of one of them?
(1) he placed a ball on an inclined plane and ascertained that the ball rolled down and continued on rolling once it leaves the inclined plane. (2)Then he placed a ball on a horizontal plane and ascertained that the ball failed to move in any respect. Then he concluded that if a body is in motion or at rest it continues to be in motion or at rest unless some external force is compelled on it. It is known as Inertia and also known as the first law of motion