The term momentum is used in various ways in everyday language, most of which are consistent with the precise scientific definition. Generally, momentum implies a tendency to continue on course—to move in the same direction; we tend to speak of sports teams or politicians gaining and maintaining the momentum to win. Momentum is also associated with great mass and speed and is often considered when talking about collisions. For example, when rugby players collide and fall to the ground, their momentums have significant effects on any resulting collisions. Momentum, like energy, is important because it is conserved; only a few physical quantities are conserved in nature, and studying them yields fundamental insight into how nature works.

The scientific definition of linear momentum is consistent with most people’s intuitive understanding of momentum: a large, fast-moving object has greater momentum than a smaller, slower object. Linear momentum is defined as the product of a system’s mass multiplied by its velocity. It is directly proportional to the object’s mass and its velocity. Thus, the greater an object’s mass or greater its velocity, the greater its momentum. Momentum is a vector that has the same direction as the velocity.

This text is adapted from Openstax, College Physics, Section 8.0: Introduction to Linear Momentum and Collisions, Section 8.1: Linear Momentum and Force, and Openstax, University Physics Volume 1, Section 9.1: Linear Momentum.