Newton:  1642-1727
•Principia published in 1687
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•3 Law of motion
–1.  A body continues at rest or in uniform motion in a straight line unless acted upon by some force.
–2.  A body’s change of motion is proportional to the force acting on it and is in the direction of the force.  
–3.  When one body exerts a force on a second body, the second body exerts an equal and opposite force back on the first body.
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•Universal gravitation
–There is an attractive force between all bodies, proportional to their mass, and inversely proportional to the square of their distance.
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