Overview

Momentum is a fundamental concept in biomechanics and physics that helps explain how objects and bodies move. In sport and physical activity, understanding linear and angular momentum is essential for analysing motion, improving performance, and designing effective movement strategies. Both types of momentum describe how mass and motion combine, but they apply to different forms of movement.

Linear momentum refers to the motion of an object or body moving in a straight line. It is calculated using the formula:

Linear momentum = mass × velocity

This means that a heavier object or an object moving faster will have greater momentum. For example, a sprinter accelerating down the track or a rugby player charging towards the try line generates significant linear momentum. To change an object’s linear momentum, a force must be applied over time—this is known as impulse. A greater impulse results in a greater change in momentum, which is crucial in activities such as jumping, throwing, or sprint starts.

Conservation of linear momentum also applies in sport. In a closed system with no external forces, total momentum remains constant. For example, in a collision between two players or in a ball-to-bat impact, the total momentum before and after must be equal. Understanding how to control or redirect momentum can affect outcomes in tackling, passing, or rebounding scenarios.

Angular momentum, on the other hand, refers to the motion of a rotating object or body part around an axis. It is calculated using the formula:

Angular momentum = moment of inertia × angular velocity

Moment of inertia depends on the mass of an object and how that mass is distributed relative to the axis of rotation.

Angular velocity is the rate at which an object rotates.

In sports such as gymnastics, diving, or figure skating, athletes utilise angular momentum to execute rotations. When an athlete pulls their limbs closer to their body (reducing the moment of inertia), they spin faster, even though their total angular momentum remains the same. This is known as the conservation of angular momentum.

An example is a gymnast in mid-air. By tucking into a compact shape, they reduce their moment of inertia and increase their angular velocity, allowing them to complete more twists or somersaults before landing. Similarly, when arms or legs are extended, rotation slows down due to an increased moment of inertia.

Angular momentum is also significant in sports that involve striking. A tennis player or golfer rotates the trunk and hips to generate angular momentum, which is transferred down the body into the racket or club, and then into the ball, resulting in powerful, controlled motion.

Together, linear and angular momentum explain how movement is generated, controlled, and transferred in physical activity. By applying these principles, athletes and coaches can enhance their technique, optimise movement patterns, and gain a better understanding of the mechanics behind performance.