Sir Isaac Newton was considered by many the most important figure in the development of modern science, and his accomplishments covered a broad scope, from fundamental contributions to physics and astronomy, to the invention (in parallel with Liebnitz) of the mathematical field of calculus, and Newtonian mechanics, which came to be regarded as the ultimate explanatory science (Clockwork; Sir Isaac). Newton changed the understanding of the universe with his three laws of motion. Newton's First Law of Motion states that every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it (Newton's). This is basically Galileo's law of inertia. Newton's Second Law of Motion states that the relationship between an object's mass m, its acceleration a, and its applied force F is F=ma. Force and acceleration are vectors and this is indicated by their symbols being in bold Italics. In this law, the direction of these two vectors is the same. This is the most powerful of Newton's Laws because it allows quantitative calculations of dynamics. Newton's Third Law of Motion is that for every action there is an equal and opposite reaction.
In the example of an apple falling from a tree, by Newton's Second Law of Motion, there must be a force that acts on the apple to cause it to accelerate from zero when it is hanging on the tree to its movement towards the ground (Sir Isaac Newton: The Universal). Newton reasoned that the force of gravity might reach all the way to the orbit of the Moon. From this, he reasoned that the Moon's orbit around the Earth could be the consequence of the gravitational force because the acceleration due to gravity could change the velocity of the Moon in such a way that it followed an orbit around the Earth. This led him to reason that any two objects in the Universe exert gravitational attraction on each other with the forces having a universal form. ...