Sir Isaac Newton founded three physical laws of motion. They lay the foundation of classical mechanics. The laws describe the relationship between a body and the forces acting upon it. The laws can be expressed in different ways.

The first law states that an object at rest will remain at rest unless acted upon by a force. An object in motion will remain in motion and at a constant velocity unless acted upon by a force.

The second law states that the acceleration of a body is directly proportional to, and in the same direction as, the net force acting on the body and inversely proportional to its mass. This F = ma is stated. Where F is the net force acting on an object, m is the mass of the object and a is the acceleration of the object.

The third law states that when one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direct to that of the first body.

Sir Isaac Newton first published his three laws of motion in 1687 in Mathematical Principles of Natural Philosophy [1]. He used the laws to explain the motion of physical objects and systems. These laws were verified by experiments and observations. They are an excellent approximation of the scales and speeds of everyday life.

See the *Principia* on line at Andrew Motte Translation