How many laws of motion did Isaac Newton formulate?

Isaac Newton formulated three laws of motion. These laws describe how forces affect the motion of objects and form the foundation of classical, or Newtonian, mechanics.

Newton presented the laws in his 1687 work Philosophiæ Naturalis Principia Mathematica, commonly called the Principia. The first law is the law of inertia: an object remains at rest or moves at constant velocity unless acted on by a net external force. The second law connects force, mass, and acceleration. The third law states that interacting bodies exert equal and opposite forces on each other.

A common mix-up is confusing Newton’s three laws of motion with his law of universal gravitation. Gravity is a separate theory, although the laws of motion can be used to analyze gravitational motion. Another neighbouring fact is that Newton’s second law is often written F = ma for constant mass, while its more general form relates force to the rate of change of momentum.

The laws were revolutionary because they provided a unified mathematical framework for explaining motion on Earth and, to a large extent, the motion of celestial bodies.