5.3
Before Galileo and Newton, scientists held a 2000-year-old belief that objects have a natural tendency to come to rest if left alone.
Also, a constant force is necessary to keep them moving.
Galileo disproved this idea with a thought experiment using a bronze ball that is rolled over smooth double inclined planes.
A ball rolled down from the first plane runs up the same height on the second plane.
If the second plane has a smaller inclination angle, the ball moves to a longer distance to reach the same height.
If the second plane is horizontal, the ball should keep moving forever to reach the same height.
Galileo concluded that force is not required to keep a body in motion.
Newton summarized these and other observations in three laws of motion that are fundamental to mechanics.
The first law states that every object remains stationary or under a constant velocity unless acted on by a net external force.
Motion draws our attention. Motion itself can be beautiful, causing us to marvel at the forces needed to create spectacular sights, such as that of a…
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