| Newtonian mechanics, which includes Newton's three | | | | commonly expressed by the formula F=ma, where F |
| laws of motion as well as the law of gravity, is an | | | | is the force acting on the object, m is its mass, and a is |
| amazingly precise theory of the dynamics of material | | | | its acceleration. The third law says that for every |
| bodies. Newtonian mechanics replaced Aristotilian | | | | action there is an equal and opposite reaction. This law |
| natural philosophy shortly after it was proposed. As | | | | is equivalent to the conservation of momentum. It is the |
| expressed in Newton's manuscript Philosophae | | | | principle behind rocket engines. |
| Naturalis Principia Mathematica (Mathematical Principles | | | | The remaining piece is Newton's law of universal |
| of Natural Philosophy), published in 1687, Newtonian | | | | gravitation. This law states that two point masses |
| mechanics remained unchallenged for over 200 years. | | | | experience an attractive gravitational force proportional |
| The starting point of Newtonian mechanics is Newton's | | | | to the product of their masses and inversely |
| three laws of motion. The first law, known as the law | | | | proportional to the square of the distance separating |
| of inertia, states that an object at rest will remain at | | | | them. This is expressed mathematically by the formula |
| rest and that an object in motion will remain in motion | | | | F = GMm/r^2, where M is the mass of the first body, |
| at constant velocity (speed and direction) unless acted | | | | m is the mass of the second body, r is the distance |
| upon by an outside force. The second law states that | | | | separating the two bodies, and G is a constant known |
| if an outside force acts upon an object, the object will | | | | as the universal gravitational constant. This law |
| accelerate by an amount proportional to the force and | | | | explains how objects fall as well as how the orbital |
| inversely proportional to its mass. This is more | | | | motions of the moon and planets. |