The general principles of dynamics
are rules which demonstrate a relationship between the
motions of bodies and the forces which produce those
motions. Based in large part on the work of his
predecessors, Sir Isaac Newton deduced three laws of
dynamics which he published in 1687 in his famous Principia.
Prior to Newton, Aristotle had established that the natural
state of a body was a state of rest, and that unless a force
acted upon it to maintain motion, a moving body would come
to rest. Galileo had succeeded in correctly describing the
behavior of falling objects and in recording that no force
was required to maintain a body in motion.
He noted that the effect of force was to change motion.
Huygens recognized that a change in the direction of motion
involved acceleration, just as did a change in speed, and
further, that the action of a force was required. Kepler
deduced the laws describing the motion of planets around the
sun. It was primarily from Galileo and Kepler that Newton