What Causes Motion?

A force—a push or a pull—is required to change the state of motion of an object. Unbalanced forces cause acceleration, while balanced forces keep an object at rest or moving uniformly.

Newton's Laws of Motion

First Law (Law of Inertia): An object remains at rest or in uniform motion unless acted upon by an unbalanced force. Mass is the measure of inertia.

Second Law: The rate of change of momentum of an object is proportional to the applied unbalanced force. This gives us the famous equation F = ma.

Third Law: To every action, there is an equal and opposite reaction. These forces act on two different bodies simultaneously.

Conservation of Momentum

In an isolated system without external forces, the total momentum remains conserved before and after a collision. This fundamental principle governs everything from billiard balls to rocket propulsion.