:force = mass x acceleration : a planet moves faster in the part of its orbit nearer the sun and slower when farther from the sun, sweeping out equal areas in equal times. : the orbit of each planet about the sun is an ellipse with the sun at one focus. : for any force, there is an equal and opposite reaction force. : an object moves at constant velocity if there is no net force acting upon it. : more distant planets orbit the sun at slower average speeds, obeying the precise mathematical relationship p2 =a3.