1.Basically, Aristotle's view of motion is "it requires a force to make an object move in an unnatural" manner - or, more simply, "motion requires force" . After all, if you push a book, it moves. When you stop pushing, the book stops moving.

2.Galileo measured that all bodies accelerate at the same rate regardless of their size or mass. Key among his investigations are: developed the concept of motion in terms of velocity (speed and direction) through the use of inclined planes. ... objects resist change in motion, which is called inertia.